Rice nutrient

Edited by Thomas Fairhurst, Christian Witt,
Roland Buresh, and Achim Dobermann
Nutrient management
Nutrient deficiencies
Mineral toxicities
Tools and information
A Practical Guide to Nutrient Management
Rice
Revised
2007 Edition

Rice: A Practical Guide to Nutrient Management (2nd
edition)
Edited by T.H. Fairhurst, C. Witt, R.J. Buresh, and A. Dobermann
Attribution-NonCommercial-ShareAlike 3.0 Unported. Unless otherwise
specifically stated in this publication, users are free to distribute, display, and
transmit the work and to adapt the work under the conditions described at
http://creativecommons.org/licenses/by-nc-sa/3.0/
Limits of liability
Although the authors have used their best efforts to ensure that the contents
of this book are correct at the time of printing, it is impossible to cover all
situations. The information is distributed on an “as is” basis, without warranty.
Neither the authors nor the publishers shall be responsible for any liability,
loss of profit, or other damages caused or alleged to have been directly or
indirectly caused by following guidelines in this book.
Typesetting & layout by Tham Sin Chee.
First edition 2002. Reprinted 2003, 2005.
Second edition 2007.
ISBN 978-981-05-7949-4
About the publishers
IRRI’s mission is to reduce poverty and hunger, improve the health of rice
farmers and consumers, and ensure environmental sustainability through
collaborative research, partnerships, and the strengthening of national
agricultural research and extension systems.
IPNI’s mission is to help define the basis for appropriate use and management
of plant nutrients, especially focusing on the environmental and economic
issues related to their use and to provide comprehensive and regional
information and research results to help farmers, and the industry, deal with
environmental and agronomic problems.
IPI’s mission is to develop and promote balanced fertilization for the
production of higher yields and more nutritious food, together with ensuring
sustainability of production through conservation of soil fertility for future
generations.
2007 International Rice Research Institute,
International Plant Nutrition Institute, and
International Potash Institute.

i
Foreword
Food security in Asia depends largely on intensive rice production
in the favorable environments of irrigated rice-based cropping
systems. Further increases in productivity are needed because
of predicted growth in population and decreased availability of
water and land. Future yield increases will require improved crop
care, integrated resource management approaches, and more
knowledge-intensive strategies for the efficient use of all inputs,
including fertilizer nutrients.
Site-specific nutrient management (SSNM) concepts have
been developed in recent years as alternatives to the use of
blanket fertilizer recommendations over large areas. These new
approaches aim to achieve more efficient fertilizer use. Balanced
fertilization increases profit to farmers, results in higher yields
per unit of applied fertilizer, and protects the environment by
preventing excessive use of fertilizer. SSNM strategies have
been evaluated successfully in a wide range of farmers’ fields
in Asia and are now positioned for wider-scale validation and
adaptation by farmers in Asia.
This publication is a practical guide for detecting nutrient
deficiency and toxicity symptoms and managing nutrients in rice
grown in tropical and subtropical regions. The guide follows up
on an earlier IRRI/PPI-PPIC publication, Rice: Nutrient Disorders
and Nutrient Management, and is designed for translation and
publication in other languages.
We hope that this guide will find wide dissemination and
contribute to the delivery of proper nutrient management
strategies to Asia’s rice farmers.
Ronald P. Cantrell
Director General, International Rice Research Institute
Thomas Fairhurst
Director, PPI-PPIC East & Southeast Asia Programs

ii
Foreword to the 2nd Edition
In the last five years, site-specific nutrient management (SSNM)
for rice has become an integral part of initiatives on improving
nutrient management in many Asian countries. Nutrient
recommendations were tailored to location-specific needs,
evaluated together with rice farmers, and promoted through
public and private partnerships on a wide scale. The first edition
of Rice: A Practical Guide to Nutrient Management published in
2002 quickly became the standard reference for printed materials
on SSNM. The guide was high in demand with 2,000 copies
distributed and sold to date.
Over the years, SSNM has been continually refined through
research and evaluation as part of the Irrigated Rice Research
Consortium. Conceptual improvements and simplifications were
made, particularly in nitrogen management. A standardized 4-
panel leaf color chart (LCC) was produced and the promotion of
the new LCC continues with more than 250,000 units distributed
until the end of 2006. A new SSNM Web site was developed
(www.irri.org/irrc/ssnm) to provide up-to-date information and
local recommendations for major rice-growing areas in Asia. The
revised edition of the practical guide thus became necessary
to be consistent with newer information provided on the SSNM
Web site and in local training materials. We are pleased that this
2nd edition is about to be translated into a number of languages,
including Bangla, Chinese, Hindi, Indonesian, and Vietnamese.
We hope that this guide will continue to benefit Asia’s rice
farmers in their efforts to improve yields and income through
appropriate nutrient management.
Robert S. Zeigler
Director General, International Rice Research Institute
Christian Witt
Director, IPNI-IPI Southeast Asia Program

Acknowledgments
We wish to acknowledge the following people and organizations:
4 J.K. Ladha, David Dawe, and Mark Bell for many helpful
comments and suggestions during our struggle to condense
the material into a practical format.
4 Former and current staff members of IRRI, especially
Kenneth G. Cassman and John E. Sheehy, for key conceptu-
al contributions to the development of plant-based N man-
agement and yield potential analysis in rice; and Heinz-Ulrich
Neue and the late Dharmawansa Senadhira for pictures and
unpublished material on nutrient deficiencies and toxicities.
4 All scientists, extension staff, and farmers participating in the
Irrigated Rice Research Consortium for their many valuable
comments and suggestions.
4 All scientists who contributed to this guide through their
publications. This guide is not referenced as it builds on an
earlier work mentioned in the foreword.
4 Bill Hardy (IRRI) for his help in the preparation of this guide.
4 Elsevier Science for permission to reprint a photograph from
Crop Protection Vol. 16 (Datnoff L, Silicon fertilization for
disease management of rice in Florida); Helmut von Uexküll
and Jose Espinosa (IPNI); Pedro Sánchez (ICRAF); Mathias
Becker (University of Bonn, Germany); Frank Mussgnug
(ZEF, Germany); Lawrence Datnoff (University of Florida,
USA); and Takeshi Shimizu (Osaka Prefecture Agriculture &
Forestry Research Center, Japan) for providing slides and
photographs.
4 The Swiss Agency for Development and Cooperation (SDC),
International Fertilizer Industry Association (IFA), International
Plant Nutrition Institute (IPNI), International Potash Institute
(IPI), and IRRI for long-term funding for the development and
dissemination of SSNM for rice, including financial support for
producing this guide.
iii

Table of contents
Foreword..............................................................................i
Foreword to the 2nd Edition................................................ii
Acknowledgments.............................................................. iii
1 Nutrient Management.......................................................1
1.1 Relevance and causes of yield gaps..................................1
1.2 Basic concepts of balanced N, P, and K management.......5
1.3 Fertilizer-use efficiencies....................................................7
1.4 Site-specific nutrient management (SSNM)........................8
1.5 Developing a fertilizer program...........................................9
1.6 Needs and opportunity assessment..................................11
1.7 Recommendation domains...............................................14
1.8 Development of fertilizer N, P, and K recommendations...15
Step 1. Selecting an economic yield target................. 18
Step 2. Estimating soil nutrient supplies...................... 18
Step 3. Calculating fertilizer N rates and use of
real‑time N management.............................................. 21
Step 4. Calculating fertilizer P2
O5
rates ....................... 31
Step 5. Calculating fertilizer K2
O rates......................... 34
1.9 Managing organic manures, straw, and green manure.....38
1.10 Evaluation of strategies for wider-scale dissemination.....42
1.11 Useful numbers.................................................................43
2 Mineral Deficiencies and Toxicities...............................46
2.1 Nitrogen deficiency...........................................................46
2.2 Phosphorus deficiency......................................................48
2.3 Potassium deficiency........................................................50
2.4 Zinc deficiency..................................................................53
2.5 Sulfur deficiency................................................................56
2.6 Silicon deficiency..............................................................59
iv

v
2.7 Magnesium deficiency......................................................61
2.8 Calcium deficiency............................................................63
2.9 Iron deficiency...................................................................65
2.10 Manganese deficiency......................................................67
2.11 Copper deficiency.............................................................69
2.12 Boron deficiency...............................................................71
2.13 Iron toxicity........................................................................73
2.14 Sulfide toxicity...................................................................76
2.15 Boron toxicity....................................................................79
2.16 Manganese toxicity...........................................................81
2.17 Aluminum toxicity..............................................................83
2.18 Salinity..............................................................................85

Annex
Field management of rice...............................................A-2
Nutrient management tools: omission plots....................A-4
Nutrient management tools: leaf color chart (LCC).........A-6
Growth stages.................................................................A-8
Diagnostic key for identifying nutrient deficiencies
in rice............................................................................A-10
Nitrogen-deficiency symptoms......................................A-12
Phosphorus-deficiency symptoms................................A-14
Potassium-deficiency symptoms...................................A-16
Zinc-deficiency symptoms.............................................A-18
Sulfur-deficiency symptoms..........................................A-20
Silicon-deficiency symptoms.........................................A-22
Magnesium-deficiency symptoms.................................A-24
Calcium-deficiency symptoms......................................A-26
Iron-deficiency symptoms.............................................A-28
Manganese-deficiency symptoms.................................A-30
Copper-deficiency symptoms........................................A-32
Diagnostic key for identifying nutrient toxicities in rice..A-35
Iron-toxicity symptoms..................................................A-36
Sulfide-toxicity symptoms.............................................A-38
Boron-toxicity symptoms...............................................A-40
Manganese-toxicity symptoms......................................A-42
Aluminum-toxicity symptoms........................................A-44
Salinity symptoms.........................................................A-46
vi

1.1 Relevance and causes of yield gaps
Most rice farmers achieve less than 60% of the climatic and
genetic yield potential at a particular site. A simple model
can be used to illustrate the factors that explain the “yield
gap” (Fig. 1).
The yield potential or maximum yield (Ymax
) is limited by
climate and rice variety only, with all other factors at optimal
levels. Ymax
fluctuates from year to year (±10%) because
1 Nutrient Management
C. Witt1
, R.J. Buresh2
, S. Peng2
, V. Balasubramanian2
, and
A. Dobermann2
1 IPNI-IPI Southeast Asia Program, Singapore; 2 International Rice
Research Institute, Los Baños, Philippines.
Relative yield (%)
60
40
100
80
20
0
Yield reduced
because
of nutrient
imbalance
and poor
management
Yield reduced
because
of nutrient
imbalance
Economic
yield target
Yield potential
of a variety
for a given
climate
Ymax
Ya
YYtarget
Yield gap 1
(20%)
Yield gap 2
(20%)
Yield gap 3
(20%)
Fig. 1. Example for the effect of nutrient and crop management on yield
potential or maximum yield (Ymax
), yield target (Ytarget
), attainable yield
(Ya
), and actual yield (Y).

of climate. For most rice-growing environments in tropical
South and Southeast Asia, the Ymax
of currently grown high-
yielding rice varieties is about 10 t/ha in the high-yielding
season (HYS) and 7–8 t/ha in the low-yielding season (LYS).
The attainable yield (Ya
) is the “nutrient-limited” yield that
can be achieved with current farmers’ nutrient management
practices but optimal water, pest, and general crop
management. The maximum Ya
achieved by the best
farmers is about 75–80% of Ymax
(i.e., 7–8 t/ha in an HYS
and 5–6.5 t/ha in an LYS). Such an economic yield target
(Ytarget
, Fig. 1) leaves a yield gap 1 of about 20–25% of Ymax
.
In most cases, it is not economical to close this gap because
of the large amount of inputs required and the high risk of
crop failure because of lodging or pest attacks. In reality,
Ya
is substantially lower in most farmers’ fields because of
inefficient fertilizer N use or nutrient imbalances that result
in a larger yield gap (yield gap 2) (Fig. 1).
The actual yield (Y) in farmers’ fields is often lower than
Ya
because of constraints other than climate and nutrient
supply, such as seed quality; weeds, pests, and diseases;
mineral toxicities; and water supply (yield gap 3).
Understanding yield gaps is important because they result in
4 reduced profit for farmers,
4 reduced return on investments in rice research and
development (e.g., irrigation facilities), and
4 reduced rice production, resulting in food insecurity and
increased requirements for rice imports.
Improved nutrient management can help to reduce yield
gap 2 for the benefit of farmers and the country as a whole.
The greatest benefit from improved nutrient management,
however, is found on farms with good crop management
and few pest problems. Farmers need to know what factors
can be changed to increase productivity (knowledge-based

management) and should know that larger yield increases
result when several constraints (e.g., pest and disease
problems and inappropriate nutrient management) are
overcome simultaneously.
Crop management
Many general crop management practices affect crop
response to improved nutrient management.
Consider the following points:
4 Use high-quality seed of a suitable high-yielding variety.
4 Transplant young seedlings (e.g., 10–20 days old).
4 Level the soil properly and maintain an appropriate water
level over the whole field to achieve good crop uniformity.
This reduces overall water requirements.
4 Choose a suitable planting density to establish an efficient
leaf canopy (e.g., 20–40 hills/m2
with 1–3 plants/hill in
transplanted rice and 80–120 kg seed per ha in broadcast,
wet-seeded rice).
4 Do not allow weeds to compete with rice plants for space,
water, light, and nutrients.
The full potential of improved nutrient management can only
be reached with good crop management.
Pests and diseases
Pests and diseases affect crop response to improved
nutrient management by damaging the leaf canopy, the
plant stem, and the grain. The most common pests in
irrigated rice are sheath blight, bacterial leaf blight, stem rot,
stem borer, tungro, brown planthopper, rats, and birds.
Consider the following points:
4 Use varieties that are resistant to commonly occurring pests
and diseases.

4 Avoid excessive N fertilizer use to prevent the development
of a lush green foliage that attracts pests and diseases.
4 Before applying N fertilizer, assess the general crop stand,
leaf color (using a leaf color chart), and pest and disease
incidence.
4 Damage by many diseases (e.g., brown leaf spot, sheath
blight, bacterial leaf blight, stem rot, and blast) is greater
where excessive N fertilizer and insufficient potassium
(K) fertilizer have been used in rice crops affected by K
deficiency.
4 Practice integrated pest management (IPM) in cooperation
with other farmers.
Efficient N fertilizer use and balanced nutrition minimize the
risks of lodging, pests, and diseases.
Nutrient management
A yield target will be reached only when the correct amount
of nutrients is supplied at the right time to match the crop’s
nutrient requirement during the season.
Efficient and cost-effective nutrient management strategies
should aim to
4 maximize crop uptake of nutrients from fertilizers and
soil indigenous sources through good crop management
practices,
4 make full use of nutrients available in the form of straw,
other crop residues, and animal manures,
4 use mineral fertilizers as required to overcome specific
nutrient limitations,
4 minimize the risk of crop failure by selecting realistic and
economic yield targets and practicing the efficient use of
fertilizer and balanced nutrition, and
4 maximize revenue by considering the cost of inputs,
including labor, organic manure, and inorganic fertilizer.

1.2 Basic concepts of balanced N, P, and K
management
Nutrient input-output
The nutrient budget (B) for a rice field can be estimated as
follows (all components measured in kg nutrient per ha):
B = M + A + W + N2
- C - PS - G
where
Inputs: M is the nutrient source added (inorganic and
organic); A is atmospheric deposition (rainfall and dust); W
is irrigation water, floodwater, and sediments (dissolved and
suspended nutrients); and N2
is biological N2
fixation.
Outputs: C is net crop removal with grain and straw (total
uptake less nutrients returned in crop residues); PS is
losses from percolation and seepage; and G is total
gaseous N losses from denitrification and NH3
volatilization.
Soil indigenous nutrient supply and balanced nutrition
Indigenous nutrient supply is the amount of a particular
nutrient from all sources except mineral fertilizer (i.e., soil,
crop residues, irrigation water) available to the crop during a
cropping season.
A reliable, practical indicator of soil nutrient supply is the
nutrient-limited yield, which can be measured as grain
yield in a nutrient omission plot (e.g., N-limited yield in an
omission plot receiving fertilizer P and K but no fertilizer N;
see Step 2 in Section 1.8).
Balanced fertilization means supplying the crop with the
correct amount of all nutrients not supplied in sufficient
amounts from indigenous sources (Fig. 2).
In the early years of the Green Revolution, yield increases
were mainly achieved through the use of N fertilizers, often
subsidized by governments, in combination with modern

inbred varieties. Encouraged by the yield response, farmers
increased fertilizer N rates to what are now often excessive
levels, while applying insufficient amounts of fertilizer P and
K. This results in an unbalanced supply of nutrients to the
crop. Furthermore, nutrients that were formerly not limiting
often became limiting with increasing yield targets (Fig. 2).
Intensive rice cropping with larger yields and 2–3 crops/year
results in a risk of depleting the soil’s reserves of P and K
because
4 nutrients removed in grain may not be replaced by nutrients
contained in crop residues, organic manures, and mineral
fertilizer,
Fig. 2. Example for limitations in soil indigenous N, P, and K supply
estimated as grain yield in omission plots. For the old yield target, the
soil would have limitations in N, but not in P and K supply, whereas, for
the new yield target, soil nutrient supply would be limiting for all three
nutrients in the order NKP.
Grain yield (t/ha)
7
6
4
5
2
0
3
1
New yield target
Old yield target
0 N 0 K0 POmission plot:
Applied nutrients: +PK +NK

4 farmers remove straw (which contains large amounts of
K) from the field for use as animal bedding and fuel or for
industrial use, and
4 the amount of P and K removed with grain increases.
Note that the optimal ratio of fertilizer N:P:K to be applied is
site-specific as it depends on the yield target and the supply
of each nutrient from soil indigenous sources.
If plant growth is limited by nutrient supply only, optimal
nutritional balance is achieved with plant uptake of about 15
kg N, 2.6 kg P, and 15 kg K per ton of grain yield (Table 1).
1.3 Fertilizer-use efficiencies
Fertilizer is used efficiently when
4 a large proportion of the applied fertilizer is taken up by the
crop (termed recovery efficiency, RE) and
4 there is a large increase in yield for each kg of fertilizer
applied (termed agronomic efficiency, AE).
RE (%) = × 100
Plant N (N fertilized - N unfertilized) in kg/ha
Fertilizer N in kg/ha
AE (kg/kg) =
Grain yield (N fertilized - N unfertilized) in kg/ha
Fertilizer N in kg/ha
Table 1. Optimal plant N, P, and K uptake at harvest of modern rice
varieties.
traptnalP N P K
)dleiyniargt/ekatpugk(
niarG 8. 2
wartS 6 8.0 3
warts+niarG 5 6.2 5

Recovery efficiency and agronomic efficiency are
maximized when
4 the amount of nutrients applied takes into account the
amount supplied by the soil,
4 crops are provided with a balanced supply of all nutrients
required,
4 fertilizers are placed in the soil where uptake is greatest
(e.g., deep placement of urea tablets),
4 N fertilizers are applied according to changes in plant N
status during the growing season by using a leaf color
chart,
4 high-quality seed of adapted varieties is used,
4 general crop husbandry (e.g., weed control, plant spacing,
nursery management, water management) is carried out to
a high standard, and
4 pests and diseases are controlled using integrated pest
management techniques.
1.4 Site-specific nutrient management (SSNM)
The SSNM strategy described here aims to achieve
sustainable, large, and economic yields through proper
nutrient and crop management by
4 making efficient use of all available nutrient sources,
including organic manure, crop residues, and inorganic
fertilizer according to availability and cost,
4 following plant need-based N management strategies using
the leaf color chart (LCC),
4 using nutrient omission plots to determine the soil
indigenous nutrient supply (particularly for P and K),
4 providing the crop with a balanced supply of nutrients (N, P,
K, and micronutrients),

4 replacing nutrients (particularly P and K) removed with
grain and straw to avoid depleting soil nutrient reserves,
4 selecting the least costly combination of fertilizer sources,
4 using high-quality seeds, optimum planting density,
integrated pest management, and good crop management
to fully exploit the benefit of SSNM, and
4 adjusting SSNM to local needs (i.e., evaluate yield and
profit in farmers’ fields with farmer participation).
1.5 Developing a fertilizer program
Fertilizer programs based on SSNM can be developed
4 by farmers for individual fields or
4 by extension campaign planners for larger and
relatively uniform areas with similar soil nutrient supply
characteristics, referred to as recommendation domains
(Section 1.7).
Use participatory approaches by involving researchers,
extension workers, and local farmers in the development
of suitable fertilizer strategies. New recommendations
should also be evaluated in demonstration plots for
at least 1–2 cropping seasons before wide-scale
implementation. Table 2 gives a suggested time frame for
the development of a fertilizer program.
Notes:
✍ Remember to prioritize production constraints: Which
technologies offer the greatest potential for increased
productivity?
✍ Try not to introduce too many new recommendations
at one time. Focus on two to three technologies (e.g.,
improved seed quality and an improved fertilizer NPK
program).

10
✍ Use participatory techniques to test the new
recommendations on a limited number of farms for one or
two seasons and then adjust the recommendations based
on the feedback gathered from farmers.
✍ Nutrient deficiencies in rice are most common for N, P, and
K, but also for other nutrients such as Zn and S, particularly
with increased intensification of rice cropping.
a
Ideally a high-yielding season with favorable climatic conditions and
little pest pressure.
Table 2. Suggested time frame for the participatory development and
testing of improved nutrient management strategies.
Season Activity
Before
season 1
Select a target area. Hold stakeholder meetings.
Do a needs and opportunity assessment (NOA).
Select recommendation domains.
Develop a first improved fertilizer N strategy based
on the NOA and SSNM principles.
Season 1a
Test the newly developed fertilizer N strategy
in selected farmers’ fields with active farmer
participation.
Estimate indigenous N, P, and K supplies.
Check the validity of selected recommendation
domains.
Before
season 2
Develop fertilizer recommendations in cooperation
with farmers and extension specialists.
Seasons
2 and 3
Test and fine-tune new recommendations in
demonstration plots located in farmers’ fields.
Verify estimates of indigenous N, P, and K supplies
in seasons 2 and/or 3.
Seasons
4 and 5
Deliver fertilizer recommendations on a wider scale
in selected recommendation domains.
Monitor and evaluate!

11
1.6 Needs and opportunity assessment
At current production levels and fertilizer prices, most
profit increases in rice farming in Asia can be achieved by
increasing yield and in part by decreasing costs. Fertilizer
costs can be minimized by selecting the least costly
combination of locally available fertilizer sources and efficient
and balanced use of fertilizer (e.g., investing more in the most
limiting nutrient while saving on a less limiting nutrient).
Understanding farmers’ biophysical and socioeconomic
production constraints is of fundamental importance for
the development of an extension campaign strategy, and
this can best be achieved through a needs and opportunity
assessment (NOA):
4 evaluate current farmers’ crop, nutrient, and pest
management practices to identify management-related
constraints,
4 assess farmers’ awareness of the productivity constraints
identified during the survey,
4 assess whether there is sufficient opportunity to increase
productivity considering the farmers’ interest (and the
“opportunity cost” of the farmers’ time) and the capacity of
all stakeholders (farmers, nongovernmental organizations,
extension personnel, local government units, etc.) to
implement a program.
Selection of suitable target areas
Select a target area based on the results of the NOA,
initial field visits, discussions with stakeholders, and
administrative boundaries. Suitable target areas for the
introduction of improved nutrient management strategies will
likely have one or more of the following characteristics:
4 Insufficient or unbalanced use of fertilizer, resulting in a low
attainable yield despite high yield potential (Section 1.1).

12
Find out about local fertilizer use from farmers, fertilizer
suppliers, and extension workers.
4 Occurrence of nutrient deficiency symptoms (Section 2).
4 Occurrence of pest problems linked to nutrient imbalance or
overuse of fertilizer N (e.g., sheath blight).
4 Inefficient fertilizer N use because of high total N rates or
inadequate splitting and timing, for example, if farmers
8 use fertilizer N rates of 175 kg/ha,
8 apply large amounts of fertilizer N during early crop
growth (50 kg N per ha within the first 10 days after
transplanting/days after sowing (DAT/DAS) or 75 kg N
per ha within the first 20 DAT/DAS),
8 apply topdressings of 50 kg N per ha per split,
8 need to apply 55 kg fertilizer N per ha (120 kg urea per
ha) per ton yield increase over yield in a 0 N plot, and
8 encounter problems with lodging.
4 Evidence of strong mining of soil indigenous P or K, for
example, if farmers grow two or more crops per year at
moderate to high yield levels, and in the past five years
8 applied 20 kg P2
O5
per ha per crop or
8 applied 10 kg K2
O per ha per crop and removed most
straw.
Prices, availability, and quality of nutrient sources
Improved fertilizer practices will be adopted by farmers only if
4 the practices are shown to produce a greater economic
return for farmers and
4 high-quality mineral fertilizers are available in sufficient
quantity in the farmers’ locality.
Crosschecks on fertilizer prices and fertilizer quality should
be included as part of the NOA.

13
Gross margin analysis
Before testing new recommendations in the field, complete
a gross margin or profit analysis to determine
4 the value of all input costs expressed as grain yield (i.e., the
“breakeven yield”),
4 the additional cost of inputs required under the new
practice,
4 the additional costs (e.g., labor) required to implement the
new fertilizer practice, and
4 the net increase in profit compared with the old practice.
Willingness to change
Farmers are the most important partners in the development
of improved fertilizer recommendations and should be
consulted right from the beginning through NOAs and
participatory approaches during the validation of new
strategies.
Investigators must confirm that land, labor, and capital are
available in sufficient amounts to permit the adoption of new
technology. Investigate what sources of credit and what
interest rates apply where farmers need to borrow funds for
the purchase of inputs.
Farmers are more likely to adopt a new fertilizer program if
the strategy
4 results in a yield increase of at least 0.5 t/ha (“seeing is
believing”),
4 provides a significant increase in farm profit, and
4 can be integrated with current farmers’ overall management
practices (including labor requirements).

14
1.7 Recommendation domains
Develop fertilizer recommendations in the target area based
on an identified recommendation domain. Recommendation
domains can be developed using a minimum set of available
biophysical and socioeconomic characteristics that determine
uniformity of yield potential, indigenous nutrient supply,
and an expected response to fertilizer within the domain. A
recommendation domain can be characterized as an area with
4 one watershed boundary,
4 a common cropping system and crop calendar,
4 similar access to irrigation water,
4 similar soil fertility status (based on existing information on
soil fertility, including maps on soil texture and other soil
properties, topography, local knowledge of farmers and
extension workers), and
4 boundaries that possibly include several administrative units.
The soil fertility status in a recommendation domain can be
verified by estimating the soil indigenous nutrient supplies
using omission plots (see Section 1.8). The size of a
recommendation domain can vary widely depending on the
spatial variability of the parameters mentioned above.
Recommendations
Recommendations are then developed together with
farmers, using participatory approaches. Separate
recommendations may be provided for different
4 yield targets (or levels of inputs),
4 crop establishment methods,
4 varieties, and
4 residue management practices
to respond to the current practices, needs, and interests of
farmers in the recommendation domain.

15
1.8 Development of fertilizer N, P, and K
recommendations
This section describes how to calculate balanced fertilizer
N, P, and K rates to achieve a yield target and gives
suggestions for the timing and splitting of fertilizer N and
K (Table 3). The approach can be used by extension
campaign planners to develop a recommendation for a
larger domain (Section 1.7) or by farmers to develop a
fertilizer recommendation for a single field.
If a full fertilizer program is to be developed for a
recommendation domain, the fertilizer calculation involves
the following steps:
Step 1. Selecting an economic yield target.
Step 2. Estimating soil nutrient supplies.
Step 3. Calculating fertilizer N rates and use of plant
need‑based N management.
O5
rates.
O rates.
The methods to calculate fertilizer rates provided in this
chapter are based on the following general assumptions
that
4 high-yielding rice varieties with a harvest index of about
0.50 are used,
4 an economic yield target of not more than 75–80% of the
yield potential is selected,
4 balanced N, P, and K fertilization is followed,
4 N fertilizer is supplied in an optimal number of correctly
timed splits using the leaf color chart (LCC),
4 good crop management practices are followed, and
4 other constraints such as water supply, weed infestation,
and pests and diseases do not limit crop growth severely.

16
Table3.MatrixfordevelopingfertilizerN,P,andKrecommendations.
UnitDryseasonWetseason
Step1.Selectaneconomicyieldtarget
Yieldpotential
Actualyieldinfarmers’field(average)
Yieldtarget
t/ha
t/ha
t/ha
Step2.Estimatesoilnutrientsuppliesfromyieldinomissionplots
N-limitedyield(yieldin0Nplot)
P-limitedyield(yieldin0Pplot)
K-limitedyield(yieldin0Kplot)
t/ha
t/ha
t/ha
Step3.CalculatefertilizerNratesanduseofplantneed-basedNmanagement
Requiredyieldincrease(yieldtargetlessyieldin0Nplot)
EstimatedtotalamountofrequiredfertilizerN
EarlyNapplication(within14DATor21DAS)
t/ha
kg/ha
kg/ha
Option1:Real-timeapproach
Nratethroughouttheseason(toDAT/DAS)
CriticalLCCvalue
Readinginterval
kg/ha
Panelno.
days

17
a
L=low,M=medium,H=high.
UnitDryseasonWetseason
Option1:Fixed-timeapproach
1sttopdressingoffertilizerNatactivetillering
2ndtopdressingoffertilizerNatpanicleinitiation
Optionalextratopdressingatearlyheading
CriticalLCCvalue
kg/ha
kg/ha
kg/ha
Panelno.
Step4.CalculatefertilizerP2
O5
rates
MaintenancefertilizerP2
O5
rateskg/ha
Step5.CalculatefertilizerK2
Orates
Amountofstrawreturnedbeforeseason
MaintenancefertilizerK2
Orates
1stapplicationatDAT/DAS(%)
2ndapplicationatDAT/DAS(%)
L/M/Ha
kg/ha
kg/ha
kg/ha

18
Step 1. Selecting an economic yield target
4 Select a yield target that is based on the average yield of
the past 3–5 crops (same season) attainable with farmers’
current good crop management practices when nutrient-
related constraints are overcome (see NPK plots, Fig. 3).
4 The yield target reflects the total amount of nutrients
that must be taken up by the crop. It is location- and
season-specific, depending on climate, cultivar, and crop
management.
4 Select a yield target of not more than 75–80% of the
potential yield (Ymax
) determined with crop simulation
models. Yield targets that are too close to the potential yield
may require larger amounts of fertilizer inputs and increase
the risks of crop failure and profit losses.
4 Select a higher yield target in the high-yielding season
(favorable climatic conditions) and a moderate yield target
in lower-yielding seasons (less favorable climatic conditions
and greater risks of crop failure because of lodging or pests
and diseases).
Step 2. Estimating soil nutrient supplies
Use grain yield in nutrient omission plots (under favorable
weather conditions and good growing conditions) as an
indicator of the potential soil supply of N, P, and K in a
cropping season (Fig. 3). Use good-quality seeds and follow
proper crop management, including water and pest control.
4 Select 10–20 representative farmers’ fields for a
recommendation domain and establish a 20 m × 5 m plot
in each farmer’s field. Divide the plot into four 5 m × 5 m
omission plots (bunds must be 25 cm wide and 25 cm high
to prevent nutrient movement between plots):
0 N The N‑limited yield is measured in an N omission
plot that receives fertilizer P and K, but no fertilizer

19
N. Install bunds to prevent cross-plot contamination
when the farmer applies fertilizer N to other parts of
the field during the season.
0 P The P-limited yield is measured in a P omission plot.
The plot receives fertilizer N and K, but no fertilizer P.
Apply sufficiently large amounts of fertilizer N and K to
reach the yield target.
0 K The K-limited yield is measured in a K omission plot.
The plot receives fertilizer N and P, but no fertilizer K.
Apply sufficiently large amounts of fertilizer N and P to
reach the yield target.
NPK The attainable yield is measured in a plot that
receives fertilizer N, P, and K. Apply sufficiently large
amounts of fertilizer N, P, and K to reach the yield
target for the recommendation domain.
In 0 P, 0 K, and NPK plots, follow a proper splitting pattern
for fertilizer N to avoid lodging. Apply sufficient Zn and other
micronutrients to all plots if deficiencies of these nutrients
commonly occur.
Irrigation canal
Farmer’s field
5m
NPK
+N, +P, +K
5 m
0 N
+P, +K
5 m
0 P
+N, +K
5 m
0 K
+N, +P
5 m
Fig. 3. Design of a set of NPK and omission plots in a farmer’s field. As
much as possible, avoid field endings, where farmers turn when plowing.

20
4 At crop maturity, measure grain yield from a central 2 m
x 2.5 m area in each omission plot. Cut all panicles and
place them on a plastic sheet to prevent yield loss. Strip all
spikelets carefully, remove unfilled spikelets, and spread
the grain on the plastic sheet. Dry the grain in full sunlight
for one whole day to reach grain moisture content of about
12–16%. It may take 2–3 days to sun-dry the grain fully in a
rainy season. Express grain yield (GY) in t/ha.
4 Average the yield estimates obtained from the 10–20
farmers’ fields for each omission plot type to obtain
8 the average N-limited yield (yield in 0 N plots),
8 the average P-limited yield (yield in 0 P plots),
8 the average K-limited yield (yield in 0 K plots), and
8 the attainable yield (yield in NPK plots)
for the recommendation domain.
4 If yield measurements in the omission plots indicate large
differences in soil nutrient supply within particular areas of
your recommendation domain, consider dividing the domain
into two or more areas. As a rule of thumb, the average
yield in omission plots should differ consistently by at least
1 t/ha to justify two separate domains.
Notes:
✍ It is essential to adopt a proper N management strategy
for 0 P, 0 K, and NPK plots, as the P and K uptake of
rice is affected strongly by the management of N, the
most commonly limiting nutrient. Fertilizer N rates should
be sufficiently high to reach about 75–80% of the yield
potential, and timing and splitting of fertilizer N should
be optimal (Step 3). Do not follow the current farmers’ N
management practice in 0 P, 0 K, and NPK plots!

21
✍ Depending on yield and season, apply at least 30–45 kg
P2
O5
per ha in 0 K plots and 50–100 kg K2
O per ha in 0 P
plots.
✍ The use of GY as an indicator of potential nutrient supply
is only valid if measured in a season with favorable climatic
conditions and proper crop management. Yield should
not be limited by other factors such as the supply of other
nutrients, water supply, and pests and diseases. Do not use
data if yield losses from lodging, rats, pests, etc., were large.
✍ Nutrient supply measured as GY is smaller in wet broadcast-
seeded rice than in transplanted rice because plant-based
measures of indigenous nutrient supply are also affected
by variety and crop establishment method. It is therefore
important to measure the soil nutrient supply in farmers’
fields using the farmers’ crop establishment methods.
✍ If the current farmers’ practice includes the application of
organic fertilizers such as farmyard manure in addition
to inorganic fertilizer, apply the same amount of organic
fertilizer in each omission plot.
Step 3. Calculating fertilizer N rates and use of
plant need-based N management
Two complementary approaches (real-time and fixed-time)
have been used successfully in farmers’ fields to manage
fertilizer N efficiently. Table 3 gives the major features of
both approaches. We recommend testing both strategies
side by side using participatory approaches in farmers’
fields to evaluate their performance before wider-scale
dissemination. Consider socioeconomic factors when
developing fertilizer N management strategies (labor
availability and cost, prices of rice and fertilizer, available
fertilizer sources, current application practices).

22
Option N1: The real-time approach
Farmers often use leaf color during the cropping season as
a visual indicator of the rice crop’s nitrogen status and to
determine the need for fertilizer N application. The leaf color
chart (LCC) is an easy-to-use and inexpensive diagnostic tool
to monitor plant N status during the season and as a decision
aid to plan fertilizer N topdressings. A predetermined amount
of fertilizer N is applied when the color of rice leaves falls
below a critical LCC threshold that indicates N deficiency in
the crop. This helps farmers to adjust fertilizer N applications
to season-specific climatic conditions that affect crop growth
(termed “real-time” N management). Good real-time N
management reduces N fertilizer needs, increases N-use
efficiency, and reduces the rice crop’s susceptibility to pests
and diseases.
Basic principle of the real-time approach
The standardized LCC (see picture on front cover) as
developed and supplied by IRRI since 2003 contains four
green panels with colors ranging from yellowish green (no.
2) to dark green (no. 5). The critical LCC value, below which
a fertilizer N application is recommended, may range from 2
to 4 depending on variety and crop establishment method.
Note that the critical LCC values given in Table 4 should be
calibrated for local conditions.
Table 4. Examples of critical leaf color chart (LCC) values depending on
variety and crop establishment method.
Variety Crop establishment Critical LCC value
Scented and aromatic – 2
Semidwarf indica Direct-seeded 3
Semidwarf indica Transplanted 3.5
Hybrid Transplanted 3.5

23
Guidelines for using the leaf color chart
4 Take LCC readings once every 7 to 10 d, starting after 14
DAT for transplanted rice (TPR) or 21 DAS for wet-seeded
rice (WSR). The last reading is taken when the crop starts
flowering (first flowering). If farmers prefer to take fewer
measurements, recommend the fixed-time approach (option
N2) in which LCC readings are taken at critical crop growth
stages such as active tillering and panicle initiation (see
A‑9).
4 Choose the topmost fully expanded leaf (Y leaf) for leaf
color measurement because it is a good indicator of the N
status of rice plants. The color of a single leaf is measured
by comparing the color of the middle part of the leaf with
the colors on the chart. If the leaf color falls between two
values, the mean of the two values is taken as the LCC
reading. For example, if the leaf color lies between values 3
and 4, it is noted as 3.5.
4 During measurement, always shade the leaf being measured
with your body because the leaf color reading is affected by
the sun’s angle and sunlight intensity. If possible, the same
person should take LCC readings at the same time of day
each time measurements are taken.
4 Take readings of 10 leaves from hills chosen randomly
within a field. If six or more leaves show color values below
the established critical values, immediately apply N fertilizer.
4 Recommended N application rates for semidwarf indica
varieties are given in Table 5.
Guidelines for calibrating the leaf color chart
LCC calibration trials can be established at a research
farm or in farmers’ fields. Select 3–4 of the most common
local varieties and compare the performance of the rice crop
using different critical LCC values (e.g., 3, 3.5, and 4). Apply
fertilizer N using the LCC as described above. In addition to

24
fertilizer use, also record grain yield and yield components
(optional), qualitative scores for insect pest and disease
incidence, and the extent of lodging.
4 Choose a factorial design for on-station experiments, for
example, three varieties and three critical LCC values as
treatments in a randomized complete block design with four
replications.
4 Use farms as replicates if you decide to conduct the
calibration trials in farmers’ fields. Select at least four
farmers’ fields per variety as replicates and test 2–3 critical
LCC values in each field.
4 Include a plot without fertilizer application to calculate the
agronomic efficiency (AE, kg grain yield increase per unit
fertilizer N applied, see Section 1.3) for different treatments.
4 The critical LCC values mainly depend on variety and
crop establishment method (Table 4), while the amount
of fertilizer N to be applied per split application is season-
specific and depends mainly on the expected yield increase
as affected by climate (Table 5).
Notes:
✍ Because the LCC approach is a plant-based N management
approach, only an approximate estimate of N-limited yield
Table 5. Proposed amounts of fertilizer N to be applied to semidwarf
indica varieties each time the leaf color falls below the critical LCC value.
Expected yield
increase over
0 N plot (t/ha)
Application rate during period
after 14 DAT or 21 DAS up to
panicle initiation (kg N/ha) a
1–2 25
2–3 35
3–4 45
a
Apply about 25 kg N/ha after panicle initiation up to first flowering.

25
is required to decide on the need for early N application
before 14 DAT in transplanted rice. Elimination of an early
N application may reduce tillering in fields with low soil
N-supplying capacity. Therefore, decide whether early
application is required as outlined in option N2 (see below)
and use the LCC to fine-tune the subsequent topdressed N
applications as described in this section.
✍ LCC-based N management will be more successful
when used as part of an integrated site-specific nutrient
management strategy. To obtain an optimum response to N
fertilizer, other nutrients (P, K, S, Zn) must not be limiting.
Apply P and K as outlined in Steps 4 and 5 (see below),
and micronutrients (S, Zn) based on soil tests or local
recommendations.
✍ P deficiency (Section 2.2) may cause darker leaf color,
which leads to misleading LCC readings.
✍ Local calibration of the LCC is merited with real-time
N management. A simple instruction sheet in the local
language should accompany the chart and explain to
farmers how to determine the correct timing and amount of
N to apply to their rice crops in a particular season.
Option N2: The fixed-time approach
The fixed-time approach provides a recommendation for
the total fertilizer N requirement (kg/ha) and a plan for the
splitting and timing of applications in accordance with crop
growth stage, cropping season, variety used, and crop
establishment method.
Basic principle of the fixed-time approach:
Estimate the required total amount of fertilizer N and develop
a schedule for fertilizer N split applications. Use the LCC at
critical growth stages to adjust predetermined fertilizer N
rates.

26
Use Table 6 to derive the total fertilizer N rate based on
4 the expected yield response to fertilizer N application
calculated from the difference between yield target and yield
in 0 N plots (Steps 1 and 2) and
4 the attainable agronomic N efficiency (AEN
, see pages 7-8).
Rule of thumb: Apply 40–60 kg fertilizer N per ha for
each ton of expected grain yield response to fertilizer N
application.
Apply less N to crops in the rainy season (less sunshine,
lower yield response) and apply more N to crops in the dry
season (more sunshine, higher yield response).
Select an expected yield response of ≥ 4 t/ha over the yield
in the 0 N plot only for high-yielding seasons with very
favorable climatic conditions.
Experience in tropical Asia indicates that an AEN
of 25
is often achievable with good crop management in high-
yielding seasons, and an AEN
of 16.7 or 20 is achievable
with good crop management in low-yielding seasons.
Table 6. Fertilizer N rates according to the attainable yield response
(yield target – yield in 0 N plots) and the expected agronomic N
efficiency (AEN
, kg grain yield increase/kg fertilizer N).
Agronomic N efficiency
(∆kg grain/kg fertilizer N)
16.7 20 25
Yield response to fertilizer
N application (t/ha)
Fertilizer N rate (kg/ha)
1 60 50 40
2 120 100 80
3 180 150 120
4 3 200 160
5 3 3 200
3indicates unrealistic yield targets.

27
Note that the AEN
is usually higher at low N rate than at
high N rate. The aim of effective, environmentally sound
N management in the tropics is to achieve high, economic
yields while realizing an optimal AEN
between 16.7 and 25
kg grain increase per kg fertilizer N. In subtropical climate,
yield responses can be 5 t/ha with optimal AEN
25 kg/kg,
in which case suggested fertilizer N rates in Table 6 would
need to be adjusted.
4 Divide total fertilizer N recommendations into 2–4 split
applications. Use more splits with long-duration varieties
and in high-yielding seasons. Apply more N when the
crop demand for N is large (e.g., between mid-tillering and
flowering). Make a large single fertilizer N application of
45 kg N per ha only if weather conditions are very favorable
and crop response to N is large.
4 Use Tables 7–9 to develop approximate rates for N split
applications. Growth stages are given, but the actual
application date depends on variety (crop duration). For
tropical rice, panicle initiation is about 60 days before
harvest, and active tillering is approximately midway
between 14 DAT or 21 DAS and panicle initiation.
4 Use the following guidelines to determine the need for early
N application to young rice before 14 DAT or 21 DAS:
8 Eliminate early application when yield response is ≤1
t/ha. At yield responses between 1 and 3 t/ha, typically
apply about 20 to 30 kg N per ha. At yield response 3
t/ha, apply about 25% to 30% of the total N.
8 Reduce or eliminate early N applications when high-
quality organic materials or composts are applied.
8 Avoid large early fertilizer N applications (i.e., 50 kg
N per ha) in transplanted rice because early growth is
slow and N uptake is poor during the first 3 weeks after
transplanting.

28
8 Increase early N application for low tillering and large
panicle type varieties when old seedlings (24 days old)
or short-duration varieties are used, where the plant
spacing is wide (20 hills/m2
) to enhance tillering, or in
areas with low air and water temperature at transplanting
or sowing (e.g., at higher elevations).
8 Incorporate early N into the soil before planting or apply
early N within 14 days after transplanting or 21 days
after sowing. Use NH4
-N and not NO3
-N as an early N
source. There is no need to use the LCC with the early N
application.
4 Use the LCC to assess leaf N status and the crop needs for
N after 14 DAT and 21 DAS. Adjust fertilizer N rates upward
when leaves are yellowish green and downward when
leaves are green.
4 Apply a late N dose (e.g., at early heading) to delay leaf
senescence and enhance grain filling, but only to healthy
crops with good yield potential. Hybrid rice and large panicle
type varieties in high-yielding seasons often require an N
application at early heading. To reduce the risk of lodging
and pests, do not apply excessive amounts of N fertilizer
between panicle initiation and flowering, particularly in the
low-yielding seasons.
4 For the standardized IRRI LCC with most rice varieties,
the leaf colors mentioned in Tables 7–9 correspond to LCC
values as follows:
8 Yellowish green = LCC value 3,
8 Intermediate = LCC value 3.5 (intermediate between 3
and 4), and
8 Green = LCC value 4.
4 The fertilizer rates in Tables 7–9 are for relatively high N-
use efficiencies (agronomic N efficiency or AEN
) of about
16.7– 20 kg grain increase/kg fertilizer N applied in seasons

29
with 1–2 t/ha expected response to fertilizer N and 25 kg
grain increase/kg fertilizer N applied in seasons with 3–4
t/ha expected response to fertilizer N (see Table 6).
4 Use the LCC to monitor plant N status to optimize the
amount of split applications in relation to crop demand
and soil N supply. The N rates for specific leaf colors (LCC
values) in Tables 7–9 are intended to provide sufficient
flexibility to accommodate conditions when the crop
response to fertilizer in a given season and location differs
markedly from the expected yield increase to fertilizer N.
4 N rates in Tables 7–9 can be fine-tuned and tailored to
accommodate location-specific crop-growing conditions and
rice varieties.
1. Transplanted rice (inbred variety) (see Table 7)
With 20–40 hills/m2
, high-yielding conventional variety,
continuous flooding or intermittent irrigation. Transplanted
rice has slower leaf area development, dry matter
accumulation, and N uptake during early growth, but high
growth rates and N uptake after mid-tillering to grain filling.
2. Wet-seeded rice (see Table 7)
With 80–150 kg seed per ha, broadcast, high-yielding
conventional variety, continuous flooding after crop
emergence. Broadcast wet-seeded rice has more rapid
leaf area development, dry matter accumulation, and N
uptake during early growth, but a slower growth rate and
N uptake after panicle initiation, particularly during grain
filling. Early leaf senescence and lodging are more severe in
wet-seeded rice than in transplanted rice. Wet-seeded rice
needs little or no late N application.
3. Transplanted rice (hybrid) (see Table 8)
With 20–30 hills/m2
, hybrid rice with high yield potential,
continuous flooding or intermittent irrigation. Transplanted

30
hybrid rice often responds to late N application in high-
yielding seasons.
Table 8. An approximate fertilizer N splitting for transplanted hybrid rice
with high N-use efficiency.
Expected yield increase
over 0 N plot
1
t/ha
2
t/ha
3
t/ha
4
t/ha
Growth stage Leaf color a
Preplant to 14 DAT – 20 30 45
Active
tillering
Yellowish green 35 45 45 60
Intermediate 25 35 35 45
Green – – 25 25
Panicle
initiation
Green – 25 25 35
Early heading Yellowish green – – 20 20
a
See text on page A-6 in the Annex for corresponding LCC values.
Table 7. An approximate fertilizer N splitting for transplanted and wet-
seeded inbred rice with high N-use efficiency.
over 0 N plot
1
t/ha
2
t/ha
3
t/ha
4
t/ha
Growth stage Leaf colora
Preplant to 14 DAT or 21 DAS – 20 30 45
Active
tillering
Green – – 25 25
Panicle
initiation
Green – 25 25 35
a

31
4. Transplanted rice (large panicle type) (see Table 9)
High-yielding rice with very large panicles (panicle weight
type rice), relatively low tillering and good resistance to
lodging. Includes some new plant type rice and some hybrid
rice such as the Chinese “super” hybrid rice.
Notes:
✍ Do not topdress N when heavy rainfall is expected.
O5
rates
The major objective of P management is to prevent P
deficiency rather than treat P-deficiency symptoms. If low
soil P supply is the reason the targeted yields are not
achieved, management must focus on the buildup and
maintenance of adequate soil-available P levels to ensure
Table 9. An approximate fertilizer N splitting for large panicle type
(panicle weight type) rice.
over 0 N plot
1
t/ha
2
t/ha
3
t/ha
4
t/ha
Growth stage Leaf colora
Preplant to 14 DAT 25 30 40 50
Active
tillering
Yellowish green – 35 45 45
Intermediate – 25 35 35
Green – – 25 25
Panicle
initiation
Green 25 25 25 35
Early heading – – 25b
25b
a
b
Apply N regardless of LCC reading.

32
that P supply does not limit crop growth and N-use
efficiency.
P is not easily lost from the system, but inputs from sources
such as irrigation water and straw are generally small. P
fertilizer application has residual effects that can last several
years, and maintenance of soil P supply requires long-term
strategies tailored to site-specific conditions that consider P
inputs from all sources.
Sustainable P management requires the replenishment of
soil P reserves, especially at high yield levels in double and
triple rice-cropping systems, even if a direct yield response
to P application is not expected.
Rule of thumb: Where the soil P supply is small, apply
20 kg fertilizer P2
O5
per ha for each ton of target grain yield
increase (difference between yield target and yield in 0 P
plot).
The maintenance fertilizer P rates given in Table 10 are
designed to replenish the P removed with grain and straw,
assuming a low to moderate return of crop residues. Look
up the fertilizer P2
O5
rate based on
4 the yield target (Step 1) and
4 an estimate of soil P supply measured as yield in a 0 P
omission plot (Step 2).
Theoretically, fertilizer P application would not be required
if a yield response were not expected for the selected yield
target (i.e., if yield target = yield in nutrient omission plot).
This “zero-P fertilizer” strategy results in mining the soil of P
reserves and may affect yields in the medium to long term,
especially if other nutrient sources such as straw or manure
are not applied.

33
Table 10. Maintenance fertilizer P2
O5
rates according to yield targets and
P-limited yield in 0 P plots.
Yield target (t/ha) 4 5 6 7 8
Yield in 0 P plot
(t/ha)
Fertilizer P2
O5
rate (kg/ha)
3 20 40 60 3 3
4 15 25 40 60 3
5 0 20 30 40 60
6 0 0 25 35 45
7 0 0 0 30 40
8 0 0 0 0 35
Notes:
✍ Use a lower yield target (t/ha) in Table 10 where a yield
increase of more than 3 t/ha over the yield in the 0 P plot
would be required. Aiming at such high yield increases
would first require a buildup of soil fertility over several
seasons.
✍ To prevent mining of soil P reserves, the following rules of
thumb can also be applied:
8 If most of the straw is retained in the field (e.g., after
combine harvest or harvest of panicles only) and the
nutrient input from manure is small, apply at least 4 kg
P2
O5
per ha for each ton of grain harvested (e.g., 20 kg
P2
O5
for a yield of 5 t/ha) to replenish P removed with
grain.
8 If straw is fully removed from the field and nutrient
input from other sources (manure, water, sediment) is
small, apply at least 6 kg P2
O5
per ha for each ton of
grain harvested (e.g., 30 kg P2
O5
for a yield of 5 t/ha) to
replenish P removed with grain and straw.

34
✍ Maintenance fertilizer P rates (Table 10) can be reduced if
8 soils receive organic amendments such as farmyard
manure (see Table 13). Organic material can contribute
substantially to the buildup and maintenance of soil
P reserves depending on nutrient concentration and
amount applied. Apply organic amendments in nutrient
omission plots to assess the combined nutrient-supplying
capacity of soil and applied organic materials.
8 soils are periodically flooded with substantial nutrient
inputs from sedimentation (e.g., Mekong Delta in Vietnam).
✍ P applied to either rice or wheat has a residual effect on the
succeeding crop, but direct application to each crop is more
efficient. Phosphorus fertilizers should be incorporated in
the soil before seeding or transplanting or broadcast before
14 DAT for transplanted rice and 21 DAS for wet-seeded
rice.
✍ Fertilizer P application is not recommended if yield in a 0 P
plot with crop management, an adequate supply of all other
nutrients, and favorable conditions is greater than the yield
target.
✍ It may be necessary to reassess the soil P supply after 8–10
cropping cycles.
O rates
The general strategy for K management follows the same
principles given for P (Step 4), but the K uptake requirement
of rice is much greater than for P (Table 1). Furthermore,
80% of K taken up by rice remains in the straw after
harvest, making straw an important input source to consider
when calculating fertilizer K requirements (Table 11).
Rule of thumb: Where the soil K supply is small, apply 30
kg fertilizer K2
O per ha for each ton of target grain yield
increase (yield target – yield in 0 K plot).

35
The maintenance fertilizer K rates given in Table 12 are
designed to replenish the K removed with grain and straw
by considering the amount of straw returned to the field from
the previous crop.
Look up the required fertilizer K2
O rate in Table 12 based on
4 the yield target (Step 1),
4 the estimate of soil K supply measured as yield in a 0 K
omission plot (Step 2), and
4 the amount of K recycled with straw yield and the straw
management level in the previous season (Table 11).
Substantial mining of soil K reserves may affect yields in the
medium to long term, especially if most straw is removed.
As a minimum, sufficient K should be applied to replenish
the K removed with grain and straw.
Notes:
✍ The maintenance fertilizer K rates given in Table 12 can be
reduced if
8 soils receive organic amendments such as farmyard
manure (see Table 13 for typical K content of organic
materials). Organic material can contribute substantially
to the buildup and maintenance of soil K reserves
depending on nutrient concentration and amount applied.
Apply organic amendments in nutrient omission plots to
assess the combined nutrient-supplying capacity of soil
and applied organic materials; or
8 soils are periodically flooded with substantial nutrient
inputs from sedimentation (e.g., Mekong Delta in Vietnam).
✍ Use a lower yield target (t/ha) in Table 12 where a yield
increase of 3 t/ha over the yield in the 0 K plot would be
required. Aiming at such large yield increases would most
likely require a buildup of soil fertility over a longer period.

36
Table11.InputofKwithrecycledstrawaccordingtoyieldandstrawmanagementpracticesinthepreviousseason.
Strawmanagement
Previousseason
Low-yieldingseason
4–5t/ha
High-yieldingseason
4–5t/ha
Surfacecutandfullstrawremoval
10%strawremainingasstubble:
India,Nepal,Bangladesh,N.Vietnam
StrawKinput:
Low
(0–1tstrawrecycled)
StrawKinput:
Low
Lowcut
Shortstubble(25–30cm)inthefield,no
burningofthewholefield:
Philippines
StrawKinput:
Medium
StrawKinput:
Mediumtohigh
Highcut
Longstubble(30cm)inthefield,no
burningofthewholefield:
Philippines,Indonesia
StrawKinput:
Mediumtohigh
StrawKinput:
High
Combineharvestwithhighcut
Longstubbleplusthreshedstrawin
windrowsinthefield,burningofthe
wholefield:
Thailand,S.Vietnam,northernIndia
StrawKinput:
High
(4–5tstrawrecycled,but
20–25%PandKlosses
becauseofburning[P]and
leachingofK)
StrawKinput:
High
(6–8tstrawrecycled,but
20–25%PandKlosses
becauseofburning[P]
andleachingofK)

37
✍ Alternatively, consider the following rules of thumb:
8 If most of the straw is retained in the field (e.g., after
combine harvest) and the nutrient input from manure is
small, apply at least 3.5 kg K2
O per ha for each ton of
grain harvested (e.g., 17.5 kg K2
O for a yield of 5 t/ha) to
replenish K removed with grain.
Table 12. Maintenance fertilizer K2
O rates according to yield target, rice
straw inputs, and K-limited yield in 0 K plots.
Yield target (t/ha) 4 5 6 7 8
Straw
inputs
Yield in 0 K
plot (t/ha)
Fertilizer K2
O rate (kg/ha)
Low
( 1 t/ha)
3 45 75 105 3 3
4 30 60 90 120 3
5 45 75 105 135
6 60 90 120
7 75 105
8 90
Medium
(2–3 t/ha)
3 30 60 90 3 3
4 0 35 65 95 3
5 20 50 80 110
6 35 65 95
7 50 80
8 65
High
(4–5 t/ha)
3 30 60 90 3 3
4 0 30 60 90 3
5 0 30 60 90
6 10 35 70
7 25 55
8 40

38
8 If straw is fully removed from the field and nutrient
input from other sources (manure, water, sediment) is
small, apply at least 12 kg K2
O per ha for each ton of
grain harvested (e.g., 60 kg K2
O for a yield of 5 t/ha) to
replenish K removed with grain and straw.
✍ In the short term, fertilizer K application would not theoretically
be required if a yield response is not expected for the
selected yield target (i.e., if yield target = yield in 0 K plot).
This strategy results in mining of soil K reserves and may
affect yields in the medium to long term, especially if other
nutrient sources such as straw or manure are not applied.
✍ Small applications of potassium fertilizer can be made early
before 14 DAT or 21 DAS. Larger applications (40–120
kg K2
O per ha) should be made in two splits (50% at
early application and 50% at panicle initiation, PI). Large
applications (120 kg K2
O per ha) should be made in
three splits (1/3 early, 1/3 at PI, and 1/3 at heading to first
flowering).
1.9 Managing organic manures, straw, and
green manure
Wherever possible, nutrient sources such as farmyard
manure, straw, and green manure should be used in
combination with mineral fertilizers to provide part of the
rice crop’s nutrient requirements and to sustain soil quality
in the long run. Straw is the only major organic material
available to most rice farmers. About 40% of the N, 30–35%
of the P, 80–85% of the K, and 40–50% of the S taken up
by rice remains in the straw and stubble at crop maturity.
In many areas, however, organic manure is not available in
sufficient quantity to balance nutrient removal, and organic
manure use is more costly than the application of equivalent
amounts of nutrients as mineral fertilizer.

39
It is important to understand the fundamental differences
in decomposition patterns of organic inputs and the role of
organic matter (OM) in different rice-cropping systems:
4 In rice-nonrice crop systems (e.g., rice-wheat rotations)
or rainfed lowland or upland rice systems: longer aerobic
periods cause a more rapid and complete turnover of organic
matter. This may result in a decrease in soil OM content
with negative effects on “physical” soil quality under upland
conditions (e.g., reduced water-holding capacity, structure,
water percolation, biological activity, and P availability).
4 In intensive rice-rice(-rice) systems: residues decompose
mainly under anaerobic flooded conditions, leading to more
stable, well-conserved organic matter. Maintaining “physical”
soil quality is less critical because the soil structure is
destroyed deliberately by puddling at land preparation. The
role of OM is reduced to its direct and indirect effects on
nutrient supply. Occasionally, OM has negative effects on
crop growth by promoting mineral deficiencies (e.g., Zn) or
toxicities (e.g., Fe, sulfide) and poor root health.
Straw management and tillage
4 Incorporation of stubble and straw into the soil returns most
of the nutrients taken up by the crop (see Table 14) and
helps to conserve soil nutrient reserves in the long term.
Short-term effects on grain yield are often small (compared
with straw removal or burning), but long-term benefits are
significant. Where mineral fertilizers are used and straw is
incorporated, reserves of soil N, P, K, and Si are maintained
or even increased. Incorporation of straw and stubble when
wet soil is plowed results in a temporary immobilization of N
and transplanting should be carried out 2–3 wk after straw
incorporation; alternatively, urea N should be applied along
with straw.

40
4 Burning results in the loss of almost all the N content, P
losses of about 25%, indirect K losses of 20% because of
leaching, and S losses of 5–60%. Where S-free mineral
fertilizers are used, straw may be an important source of S
and thus straw burning should not be practiced. In contrast,
burning effectively transforms straw into a mineral K nutrient
source and only a small amount of K is lost in the process.
Spread the straw uniformly in the field to avoid creating
“nutrient hot spots.”
4 The effect of straw removal on long-term soil fertility is
much greater for K than for P (Table 1). Straw spreading
and incorporation, however, are labor-intensive and farmers
consider burning to be more expedient. Straw is also
an important source of micronutrients (Zn) and the most
important influence on the cumulative Si balance in rice
(Section 2.6).
4 Early, dry shallow tillage (5–10 cm depth) to incorporate
crop residues and enhance soil aeration during fallow
periods increases N availability up to the vegetative growth
phase of the succeeding rice crop. Shallow tillage of dry
soil requires a 4-wheel tractor and should be carried out
up to 2–3 wk after harvest in cropping systems where the
dry-moist fallow period between two crops is at least 30 d.
However, additional fuel and labor costs must be considered
in an economic analysis.
4 Increase the indigenous N-supplying power of permanently
submerged soils by periodic drainage and drying. An
example is midseason drainage of 5–7 d at the late tillering
stage (about 35 d after planting).
Management of other organic materials
4 Organic manures differ widely in their composition and
effect on soil fertility and nutrient supply (Table 13). Where
they are available, apply 2–10 t/ha (or more) of farmyard
manure (FYM) or other available organic materials (crop

41
residues, compost) on soils containing a small amount
of organic matter, particularly in rainfed lowland rice and
intensive irrigated rice systems where rice is rotated with
other upland crops such as wheat or maize. Avoid large
organic matter inputs shortly before crop establishment.
4 Many green manure legumes such as the fast-growing,
short-duration, stem-nodulating sesbania (Sesbania rostrata)
can accumulate N rapidly (80–100 kg N per ha in 45–60
d of growth). Most of the N (about 80%) is derived from
biological N2
fixation. Green manures decompose rapidly
when incorporated in the soil and may provide a substitute
for fertilizer N applications, especially during vegetative
growth. Use a leaf color chart to decide on the need to apply
additional fertilizer N. Green manures may improve soil
Table 13. Typical nutrient contents of organic materials.
a
kg nutrient per t fresh manure = % nutrient content × 10
Organic materiala
Water C N P K Ca
(%) (% of fresh material)
Human feces 1.0 0.2 0.3
Cattle feces 0.3 0.1 0.1
Pig feces 0.5 0.2 0.4
Fresh cattle
manure
60 8–10 0.4–0.6 0.1–0.2 0.4–0.6 0.2–0.4
Composted cattle
manure
35 30–35 1.5 1.2 2.1 2.0
Pig manure 80 5–10 0.7–1.0 0.2–0.3 0.5–0.7 1.2
Poultry manure 55 15 1.4–1.6 0.5–0.8 0.7–0.8 2.3
Garbage compost 40 16 0.6 0.2 0.3 1.1
Sewage sludge 50 17 1.6 0.8 0.2 1.6
Sugarcane filter
cake
75–80 8 0.3 0.2 0.1 0.5
Castor bean cake 10 45 4.5 0.7 1.1 1.8

42
physical properties, but have little potential for increasing
soil organic matter over time. Green manuring is effective in
accelerating the reclamation of saline and sodic soils.
4 Grow catch crops (legumes, other green manures,
managed weeds) in fallow periods of rice-nonrice rotations
to conserve N and produce additional organic matter and
income (grain legumes) if soil moisture and farm economics
allow.
1.10 Evaluation of strategies for wider-scale
dissemination
Evaluate each newly developed nutrient management
strategy in plots of at least 500–1,000 m2
embedded in
farmers’ fields.
4 Consider two demonstration plots if more than one factor
was changed to demonstrate the contribution of each factor
to yield (e.g., demonstrate the effect of improved seed
quality in one demonstration plot and improved seed quality
plus improved nutrient management in a second plot).
4 Measure grain yield and monitor fertilizer use.
4 Refine the recommendations after on-farm participatory
evaluation and gross margin analysis before dissemination
at a larger scale. Identify non-nutrient-related constraints
encountered during implementation.
4 Develop extension material such as posters or a one-page
handout for farmers and extension staff containing season-
specific “golden rules” on nutrient and crop management
(e.g., variety, seedling age, planting density, land leveling,
fertilizer N, P, and K recommendations, use of LCC, etc.).
What if the yield target is not achieved?
4 If the yield target is not achieved (actual yield 80% of
yield target), try to eliminate other constraints. Site-specific

43
nutrient management has been proved to increase yields
even on farms where nutrient-use efficiency was poor
because of general crop management problems (water,
weeds, etc.). Lowering the yield target and reducing inputs
to increase nutrient efficiencies under such conditions
may lead to a further reduction in actual yield and profit.
To increase yield and profit, other constraints should be
identified and eliminated first.
4 Lowering the yield target (and reducing inputs) is
recommended if the current high level of nutrient (mostly N)
inputs is associated with a high risk of crop failure caused
by increased pest pressure or lodging.
1.11 Useful numbers
Useful numbers for calculating the average nutrient removal
with grain and straw are given in this section (Table 14).
Conversion factors for nutrients are also included (Table
15).
Table 14. Average nutrient removal of modern irrigated rice varieties and
mineral concentrations in grain and straw.
N P K nZ S iS
)dleiyniargt/gk(warts+niarghtiwlavomertneirtunlatoT
5.7 0.3 0.7 50.0 8. 08
)dleiyniargt/niargnitneirtungk(niarghtiwlavomertneirtuN
5.0 0.2 5.2 20.0 0. 5
)dleiyniargt/wartsnitneirtungk(wartshtiwlavomertneirtuN
0.7 0. 5.4 30.0 8.0 56
)%(niargnitnetnoclareniM
0. 02.0 2.0 200.0 00.0 0.2
)%(wartsnitnetnoclareniM
56.0 0.0 04. 300.0 570.0 5.5
gM aC eF nM uC B
5.3 0.4 05.0 05.0 20.0 50.0

44
Table 14 (continued.)
56.0 0.0 04. 300.0 570.0 5.5
gM aC eF nM uC B
5.3 0.4 05.0 05.0 20.0 50.0
)dleiyniargt/niargnitneirtungk(niarghtiwlavomertneirtuN
5. 5.0 02.0 50.0 00.0 500.0
)dleiyniargt/wartsnitneirtungk(wartshtiwlavomertneirtuN
0.2 5.3 03.0 54.0 300.0 00.0
)%(niargnitnetnoclareniM
5.0 50.0 520.0 500.0 000.0 500.0
)%(wartsnitnetnoclareniM
02.0 03.0 530.0 540.0 3000.0 000.0
Table 15. Conversion factors for nutrients.
From multiply by to get/ From multiply by to get
NO3
-
0.226 N 4.426 NO3
-
NH3
0.823 N 1.216 NH3
NH4
+
0.777 N 1.288 NH4
+
CO(NH2
)2
-urea 0.467 N 2.143 CO(NH2
)2
-urea
(NH4
)2
SO4
0.212 N 4.716 (NH4
)2
SO4
NH4
NO3
0.350 N 2.857 NH4
NO3
P2
O5
0.436 P 2.292 P2
O5
Ca3
(PO4
)2
0.458 P2
O5
2.185 Ca3
(PO4
)2
K2
O 0.830 K 1.205 K2
O
KCl 0.632 K2
O 1.583 KCl
KCl 0.524 K 1.907 KCl
ZnSO4
• H2
O 0.364 Zn 2.745 ZnSO4
• H2
O
ZnSO4
• 7H2
O 0.227 Zn 4.398 ZnSO4
• 7H2
O
SO2
0.500 S 1.998 SO2
SO4
2-
0.334 S 2.996 SO4
2-

45
From multiply by to get/ From multiply by to get
MgSO4
0.266 S 3.754 MgSO4
MgSO4
• H2
O 0.232 S 4.316 MgSO4
• H2
O
MgSO4
• 7H2
O 0.130 S 7.688 MgSO4
• 7H2
O
(NH4
)2
SO4
0.243 S 4.121 (NH4
)2
SO4
SiO2
0.468 Si 2.139 SiO2
CaSiO3
0.242 Si 4.135 CaSiO3
MgSiO3
0.280 Si 3.574 MgSiO3
MgO 0.603 Mg 1.658 MgO
MgO 2.987 MgSO4
0.355 MgO
MgO 3.434 MgSO4
• H2
O 0.291 MgO
MgO 6.116 MgSO4
• 7H2
O 0.164 MgO
MgO 2.092 MgCO3
0.478 MgO
CaO 0.715 Ca 1.399 CaO
CaCO3
0.560 CaO 1.785 CaCO3
CaCl2
0.358 Ca 2.794 CaCl2
CaSO4
0.294 Ca 3.397 CaSO4
Ca3
(PO4
)2
0.388 Ca 2.580 Ca3
(PO4
)2
FeSO4
0.368 Fe 2.720 FeSO4
MnSO4
0.364 Mn 2.748 MnSO4
MnCl2
0.437 Mn 2.090 MnCl2
MnCO3
0.478 Mn 2.092 MnCO3
MnO2
0.632 Mn 1.582 MnO2
CuSO4
• H2
O 0.358 Cu 2.795 CuSO4
• H2
O
CuSO4
• 5H2
O 0.255 Cu 3.939 CuSO4
• 5H2
O
Na2
B4
O7
• 5H2
O 0.138 B 7.246 Na2
B4
O7
• 5H2
O
Na2
B4
O7
• 7H2
O 0.123 B 8.130 Na2
B4
O7
• 7H2
O
B 3.230 B2
O3
0.310 B
Table 15 (continued.)

46
2.1 Nitrogen deficiency
Function and mobility of N
Nitrogen promotes rapid growth and increases leaf size and
spikelet number per panicle. N affects all parameters that
contribute to yield. Leaf color, an indicator of crop N status,
is closely related to the rate of leaf photosynthesis and crop
production. When sufficient N is applied to the crop, the
demand for other nutrients such as P and K increases.
N-deficiency symptoms and effects on growth
Stunted, yellowish plants. Older leaves or whole plants are
yellowish green (Annex A-7, A-10, A-13).
Causes of N deficiency
4 Low soil N-supplying power.
4 Insufficient application of mineral N fertilizer.
4 Low N fertilizer-use efficiency (losses from volatilization,
denitrification, incorrect timing and placement, leaching, or
runoff).
The soil N supply is commonly not sufficient to support
higher yields of modern varieties so that N deficiency is
common in all major rice-growing areas. Significant yield
responses to fertilizer N are obtained in nearly all lowland
rice soils.
2 Mineral Deficiencies and Toxicities
T. Fairhurst1
, A. Dobermann2
, C. Quijano-Guerta2
, and
V. Balasubramanian2
1 CTP Holdings Pte Ltd., Singapore; 2 International Rice Research
Institute, Los Baños, Philippines.

47
Occurrence of N deficiency
4 Soils with very low soil organic matter content (e.g., 0.5%
organic C, coarse-textured acid soils).
4 Soils with poor indigenous N supply (e.g., acid-sulfate soils,
saline soils, P-deficient soils, poorly drained wetland soils).
4 Alkaline and calcareous soils poor in soil organic matter.
Effect of submergence on N availability and uptake
If NH4
-N fertilizers (e.g., urea) are incorporated into the
reduced soil layer after submergence, NH4
+
is adsorbed on
soil colloids, temporarily immobilized by soil microbes, or
bound abiotically to components of soil organic matter such
as phenol compounds. Losses from percolation are usually
small, except in very coarse-textured soils.
Topdressed urea is rapidly hydrolyzed (within 2–4 days)
and is susceptible to loss by NH3
volatilization. After the
midtillering phase, by which time a dense root system with
many superficial roots has formed, plant uptake rates of N
broadcast into standing water may be large (≤10 kg per ha
and day) such that losses from NH3
volatilization are small.
General N management
Treatment of N deficiency is easy and response to N
fertilizer is rapid. The response may already be evident after
2–3 days (greening, improved vegetative growth). Dynamic
soil-based and plant-based management are required to
optimize N-use efficiency for each season (see Section 1.8).

48
PotesnopseR PneslO )gkrepPgm(P1-yarB
ylekilylhgiH 5 7
elbaborP 5- 01 7- 02
sdleiyhgihtaylnO 01 02
2.2 Phosphorus deficiency
Function and mobility of P
Phosphorus is essential for energy storage and transfer in
plants. P is mobile within the plant and promotes tillering,
root development, early flowering, and ripening. It is
particularly important in early growth stages.
P-deficiency symptoms and effects on growth
Stunted dark green plants with erect leaves and reduced
tillering (Annex A-10, A-15).
Deficiency in soil
For lowland rice soils with little or no free CaCO3
, Olsen-P
and Bray-1 P test results can be classified as follows:
Causes of P deficiency
4 Low indigenous soil P-supplying power.
4 Insufficient application of mineral P fertilizer.
4 Low efficiency of applied P fertilizer because of high P-
fixation capacity in soil or erosion losses (in upland rice
fields only).
4 Excessive use of N fertilizer with insufficient P application.
4 Cultivar differences in susceptibility to P deficiency and
response to P fertilizer.

49
4 Crop establishment method (P deficiency is more likely
in direct-seeded rice, where plant density is high and root
systems are shallow).
Soils particularly prone to P deficiency
4 Coarse-textured soils containing small amounts of organic
matter and small P reserves.
4 Calcareous, saline, and sodic soils.
4 Volcanic (strongly P-fixing), peat, and acid-sulfate soils.
Occurrence of P deficiency
4 Excessive use of N or N + K fertilizers with insufficient P
application.
Effect of submergence on P availability and uptake
Flooding of dry soil causes an increase in the availability of
P in the soil.
General P management
P requires a long-term management strategy. P fertilizer
application provides a residual effect that can persist for
several years. Management must emphasize the buildup
and maintenance of adequate soil-available P levels to
ensure that P supply does not limit crop growth, grain yield,
and N-use efficiency (see Section 1.8).

50
2.3 Potassium deficiency
Function and mobility of K
Potassium has essential functions in plant cells and is
required for the transport of the products of photosynthesis.
K provides strength to plant cell walls and contributes to
greater canopy photosynthesis and crop growth. Unlike N
and P, K does not have a pronounced effect on tillering. K
increases the number of spikelets per panicle, percentage
of filled grains, and 1,000-grain weight.
K-deficiency symptoms and effects on growth
Dark green plants with yellowish brown leaf margins or dark
brown necrotic spots first appear on the tips of older leaves
(Annex A-10, A-17).
Incidence of diseases (brown leaf spot, cercospora leaf
spot, bacterial leaf blight, sheath blight, sheath rot, stem
rot, and blast) is greater where excessive N fertilizer and
insufficient K fertilizer have been used.
Deficiency in soil
For lowland rice soils, exchangeable K soil test results can
be classified as follows:
On lowland rice soils with strong K “fixation,” the amount of
1N NH4
OAc-extractable K is often small (0.2 cmolc /kg)
and is not a reliable soil test for assessing K supply.
KotesnopseR lomc(KelbaegnahcxE c
)gk/
ylekilylhgiH 51.0
elbaborP 51.0 - 54.0
sdleiyhgihtaylnO 54.0

51
Causes of K deficiency
4 Low soil K-supplying capacity.
4 Insufficient application of mineral K fertilizer.
4 Complete removal of straw.
4 Small inputs of K in irrigation water.
4 Low recovery efficiency of applied K fertilizer because of
high soil K-fixation capacity or leaching losses.
4 Presence of excessive amounts of reduced substances in
poorly drained soils (e.g., H2
S, organic acids, Fe2+
), resulting
in retarded root growth and K uptake.
4 Wide Na:K, Mg:K, or Ca:K ratios in soil, and sodic/saline
conditions. Excess Mg in soils derived from ultrabasic rocks.
Large bicarbonate concentration in irrigation water.
Occurrence of K deficiency
4 Excessive use of N or N + P fertilizers with insufficient K
application.
4 In direct-sown rice during early growth stages, when the
plant population is large and root system is shallow.
4 In hybrid rice because of greater demand for K.
Soils particularly prone to K deficiency
4 Coarse-textured soils with low CEC and small K reserves.
4 Highly weathered acid soils with low CEC and low K
reserves.
4 Lowland clay soils with high K fixation because of the
presence of large amounts of 2:1 layer clay minerals.
4 Soils with a large K content but very wide (Ca + Mg):K ratio.
4 Leached, “old” acid-sulfate soils.
4 Poorly drained and strongly reducing soils.
4 Organic soils.

52
Effect of submergence on K availability and uptake
Submergence results in increased solution-K concentration
and enhanced K diffusion to rice roots, particularly on
soils with a small K-fixation potential (e.g., soils containing
predominantly 1:1 layer kaolinitic clay minerals).
Flooding of dry lowland rice soils containing 2:1 layer clay
minerals may increase K fixation and reduce the solution
concentration so that rice depends on nonexchangeable
reserves for K supply.
General K management
K management should be considered part of long-term
soil fertility management because K is not easily lost from
or added to the root zone by the short-term biological and
chemical processes that affect the N supply.
K management must ensure that N-use efficiency is not
constrained by K deficiency (see Section 1.8).

53
2.4 Zinc deficiency
Function and mobility of Zn
Zinc is essential for several biochemical processes
in the rice plant. Zn accumulates in roots but can be
translocated from roots to developing plant parts. Because
little retranslocation of Zn occurs within the leaf canopy,
particularly in N-deficient plants, Zn-deficiency symptoms
are more common on younger leaves.
Zn-deficiency symptoms and effects on growth
Dusty brown spots on upper leaves of stunted plants
appearing 2–4 weeks after transplanting (Annex A-10,
A‑19).
Growth is patchy and plants are stunted.
Deficiency in soil
Critical soil levels for occurrence of Zn deficiency:
4 0.6 mg Zn per kg: 1N NH4
-acetate, pH 4.8
4 1.0 mg Zn per kg: 0.05N HCl
4 2.0 mg Zn per kg: 0.1N HCl
Causes of Zn deficiency
4 Small amount of available Zn in the soil.
4 Planted varieties are susceptible to Zn deficiency (e.g.,
IR26).
4 High pH (≥7 under anaerobic conditions).
4 High HCO3
-
concentration because of reducing conditions
in calcareous soils with high organic matter content or
because of large concentrations of HCO3
-
in irrigation water.
4 Depressed Zn uptake because of an increase in the
availability of Fe, Ca, Mg, Cu, Mn, and P after flooding.

54
4 Immobilization of Zn following large applications of P
fertilizer (P-induced Zn deficiency).
4 High P content in irrigation water (only in areas with polluted
water).
4 Large applications of organic manures and crop residues.
4 Excessive liming.
Occurrence of Zn deficiency
4 Intensively cropped soils where large amounts of N, P, and
K fertilizers (which do not contain Zn) have been applied in
the past.
4 Triple-rice crop systems.
Soils particularly prone to Zn deficiency
4 Leached, old acid-sulfate, sodic, saline-neutral, calcareous,
peat, sandy, highly weathered, acid, and coarse-textured
soils.
4 Soils with high available P and Si status.
Effect of submergence on Zn availability and uptake
Under flooded conditions, Zn availability decreases because
of the decrease in Zn solubility as pH increases.
Preventive strategies for Zn management
4 Varieties: Select Zn-efficient varieties.
4 Crop establishment: Dip seedlings or presoak seeds in a
2–4% ZnO suspension (e.g., 20–40 g ZnO per L of water).
4 Fertilizer management: Apply organic manure. Apply
5–10 kg Zn per ha as Zn sulfate, Zn oxide, or Zn chloride
as a prophylactic, either incorporated in the soil before
seeding or transplanting, or applied to the nursery seedbed
a few days before transplanting. On most soils, blanket
applications of ZnSO4
should be made every 2–8 crops.

55
4 Water management: Drain triple-cropped land periodically.
Do not use high pH (8) water for irrigation.
Treatment of Zn deficiency
Zn deficiencies are most effectively corrected by soil Zn
application. Surface application is more effective than
soil incorporation on high-pH soils. Zn sulfate is the most
commonly used Zn source (but ZnO is less costly). The
following measures, either separately or in combination,
are effective but should be implemented immediately at the
onset of symptoms:
4 If Zn-deficiency symptoms are observed in the field,
broadcast 10–25 kg ZnSO4
• H2
O or 20–40 kg ZnSO4
• 7H2
O
per ha over the soil surface. Mix the Zn sulfate (25%) with
sand (75%) for a more even application.
4 Apply 0.5–1.5 kg Zn per ha as a foliar spray (e.g., a 0.5%
ZnSO4
solution at about 200 L water per ha) for emergency
treatment of Zn deficiency in growing plants.

56
2.5 Sulfur deficiency
Function and mobility of S
Sulfur is required for protein synthesis, plant function,
and plant structure. S is also involved in carbohydrate
metabolism. It is less mobile in the plant than N so that
deficiency tends to appear first on young leaves.
S-deficiency symptoms and effect on growth
Pale green plants, light green-colored young leaves (Annex
A-10, A-21).
Deficiency in soil
S deficiency is sometimes confused with N-deficiency
symptoms. Soil tests for S are not reliable unless they
include inorganic S as well as some of the mineralizable
organic S fraction (ester sulfates).
The critical soil levels for occurrence of S deficiency:
4 5 mg S per kg: 0.05 M HCl,
4 6 mg S per kg: 0.25 M KCl heated at 40 ºC for 3 hours,
and
4 9 mg S per kg: 0.01 M Ca(H2
PO4
)2
.
Causes of S deficiency
4 Low available S content in the soil.
4 Depletion of soil S as a result of intensive cropping.
4 Use of S-free fertilizers (e.g., urea substituted for
ammonium sulfate, triple superphosphate substituted for
single superphosphate, and muriate of potash substituted
for sulfate of potash).

57
4 In many rural areas of developing countries, the amount
of S deposition in precipitation is small because of the low
levels of industrial gas emission.
4 Sulfur concentrations in groundwater, however, may range
widely. Irrigation water usually contains only small quantities
of SO4
2-
.
4 S contained in organic residues is lost during burning.
Soils particularly prone to S deficiency
4 Soils containing allophane (e.g., Andisols).
4 Soils with low organic matter status.
4 Highly weathered soils containing large amounts of Fe
oxides.
4 Sandy soils, which are easily leached.
Occurrence of S deficiency
4 S deficiency is less common in rice production areas
located near industrial centers where gas emission is great.
Effect of submergence on S availability and uptake
S availability decreases under submerged conditions.
Preventive strategies for S management
On most lowland soils, S supply from natural sources or S-
containing fertilizer is similar to or exceeds the amount of S
removed in rice grain.
S deficiency is easily corrected or prevented by using S-
containing fertilizers.
4 Natural inputs: Estimate the amount of S inputs from
atmospheric deposition.

58
4 Nursery: Apply S to the seedbed (rice nursery) in the
form of S-containing fertilizers (ammonium sulfate, single
superphosphate).
4 Fertilizer management: Replenish S removed in crop
parts by applying N and P fertilizers that contain S (e.g.,
ammonium sulfate [24% S], single superphosphate [12%
S]). This can be done at irregular intervals.
4 Straw management: Incorporate straw instead of removing
or burning it. About 40–60% of the S contained in straw is
lost on burning.
4 Soil management: Improve soil management to enhance S
uptake:
8 maintain sufficient percolation (about 5 mm/day) to avoid
excessive soil reduction or
8 carry out dry tillage after harvesting to increase the rate
of sulfide oxidation during the fallow period.
Treatment of S deficiency
If S deficiency is identified during early growth, the response
to S fertilizer is rapid and recovery from S deficiency
symptoms can occur within 5 days of S fertilizer application.
4 Where moderate S deficiency is observed, apply 10 kg S
per ha.
4 On soils with severe S deficiency, apply 20–40 kg S per ha.

59
2.6 Silicon deficiency
Function and mobility of Si
Silicon is a “beneficial” nutrient for rice. It is required for the
development of strong leaves, stems, and roots. Water-
use efficiency is reduced in Si-deficient plants because of
increased transpiration losses.
Si-deficiency symptoms and effects on growth
Soft, droopy leaves and culms (Annex A-11, A-23).
Si-deficient plants are particularly susceptible to lodging.
Soil
The critical soil concentration for occurrence of Si deficiency
is 40 mg Si per kg (1 M sodium acetate buffered at pH 4).
Causes of Si deficiency
4 Low Si-supplying power because the soil is very “old” and
strongly weathered.
4 Parent material contains small amounts of Si.
4 Removal of rice straw over long periods of intensive
cropping results in the depletion of available soil Si.
Occurrence of Si deficiency
Si deficiency is not yet common in the intensive irrigated
rice systems of tropical Asia.
Soils particularly prone to Si deficiency
4 Old, degraded paddy soils in temperate or subtropical
climates.
4 Organic soils with small mineral Si reserves.
4 Highly weathered and leached tropical soils.

60
Effect of submergence on Si availability and uptake
The amount of plant available Si increases after
submergence.
Preventive strategies for Si management
4 Natural inputs: Substantial inputs of Si from irrigation
water occur in some areas, particularly if groundwater from
landscapes with volcanic geology is used for irrigation.
4 Straw management: In the long term, Si deficiency is
prevented by not removing the straw from the field following
harvest. Recycle rice straw (5–6% Si) and rice husks (10%
Si).
4 Fertilizer management: Avoid applying excessive amounts
of N fertilizer in the absence of sufficient P + K.
Treatment of Si deficiency
Apply calcium silicate slag regularly to degraded paddy soils
or peat soils, at a rate of 1–3 t/ha.
Apply granular silicate fertilizers for more rapid correction of
Si deficiency:
4 Calcium silicate: 120–200 kg/ha
4 Potassium silicate: 40–60 kg/ha

61
2.7 Magnesium deficiency
Function and mobility of Mg
Magnesium is a constituent of chlorophyll and is involved
in photosynthesis. Mg is very mobile and is retranslocated
readily from old leaves to young leaves. Deficiency
symptoms therefore tend to occur initially in older leaves.
Mg-deficiency symptoms and effects on growth
Orange-yellow interveinal chlorosis on older leaves (Annex
A-10, A-25).
Soil
A concentration of 1 cmolc
Mg per kg soil indicates very
low soil Mg status. Concentrations of 3 cmolc
Mg per kg
are generally sufficient for rice.
Causes of Mg deficiency
4 Low available soil Mg.
4 Decreased Mg uptake because of a wide ratio of
exchangeable K:Mg (i.e., 1:1).
Occurrence of Mg deficiency
Mg deficiency is not frequently observed in the field
because adequate amounts are usually supplied in irrigation
water. Mg deficiency is more common in rainfed lowland
and upland rice, where soil Mg has been depleted as a
result of the continuous removal of Mg in crop products.
Soils particularly prone to Mg deficiency
4 Acid, low-CEC soils in uplands and lowlands.
4 Coarse-textured sandy soils with high percolation rates and
leaching losses.

62
4 Leached, old acid-sulfate soils with low base content.
Effect of submergence on Mg availability and uptake
The concentration of Mg in the soil solution tends to
increase after flooding.
Preventive strategies for Mg management
4 Crop management: Apply sufficient amounts of Mg fertilizer,
farmyard manure, or other materials to balance removal in
crop products and straw.
4 Water management: Minimize percolation rates (leaching
losses) on coarse-textured soils by compacting the subsoil
during land preparation.
4 Soil management: Minimize losses from erosion and
surface runoff in upland systems by using appropriate soil
conservation measures.
Treatment of Mg deficiency
Mg deficiency should be treated as follows:
4 Apply Mg-containing fertilizers. Rapid correction of Mg-
deficiency symptoms is achieved by applying a soluble Mg
source such as kieserite, langbeinite, or Mg chloride.
4 Foliar application of liquid fertilizers containing Mg (e.g.,
MgCl2
).
4 On acid upland soils, apply dolomite to supply Mg and
increase soil pH (to alleviate Al toxicity; Section 2.17).

63
2.8 Calcium deficiency
Function and mobility of Ca
Deficiency symptoms usually appear first on young leaves.
Ca deficiency also results in impaired root function and may
predispose the rice plant to Fe toxicity (Section 2.13).
An adequate supply of Ca increases resistance to diseases
such as bacterial leaf blight or brown spot.
Ca-deficiency symptoms and effects on growth
Chlorotic-necrotic split or rolled tips of younger leaves
(Annex A-11, A-27).
Soil
Ca deficiency is likely when soil exchangeable Ca is 1
cmolc
/kg, or when the Ca saturation is 8% of the CEC. For
optimum growth, Ca saturation of the CEC should be 20%.
Also for optimum growth, the ratio of Ca:Mg should be 3–4:1
for exchangeable soil forms and 1:1 in soil solution.
Causes of Ca deficiency
4 Small amounts of available Ca in soil (degraded, acid,
sandy soils).
4 Alkaline pH with a wide exchangeable Na:Ca ratio, resulting
in reduced Ca uptake.
4 Wide soil Fe:Ca or Mg:Ca ratios, resulting in reduced Ca
uptake.
4 Excessive N or K fertilizer application, resulting in wide NH4
:
Ca or K:Ca ratios and reduced Ca uptake.
4 Excessive P fertilizer application, which may depress
the availability of Ca (because of the formation of Ca
phosphates in alkaline soils).

64
Occurrence of Ca deficiency
Ca deficiency is very uncommon in lowland rice soils
because there is usually sufficient Ca in the soil, from
mineral fertilizer applications and irrigation water.
Soils particularly prone to Ca deficiency
4 Acid, strongly leached, low-CEC soils in uplands and lowlands.
4 Soils derived from serpentine rocks.
4 Sandy soils with high percolation rates and leaching.
Effect of submergence on Ca availability and uptake
The concentration of Ca in the soil solution tends to
increase after submergence.
Preventive strategies for Ca management
4 Crop management: Apply farmyard manure or straw
(incorporated or burned) to balance Ca removal in soils
containing small concentrations of Ca.
4 Fertilizer management: Use single superphosphate (13–20%
Ca) or triple superphosphate (9–14% Ca) as a P source.
Treatment of Ca deficiency
Ca deficiency should be treated as follows:
4 Apply CaCl2
(solid or in solution) or Ca-containing foliar
sprays for rapid treatment of severe Ca deficiency.
4 Apply gypsum on Ca-deficient high-pH soils (e.g., on sodic
and high-K soils).
4 Apply lime on acid soils to increase pH and Ca availability.
4 Apply Mg or K in conjunction with Ca because Ca may
induce deficiency of these nutrients.
4 Apply pyrites to mitigate the inhibitory effects of NaHCO3
‑rich
water on Ca uptake.

65
2.9 Iron deficiency
Function and mobility of Fe
Iron is required for photosynthesis. Fe deficiency may inhibit
K absorption. Because Fe is not mobile within rice plants,
young leaves are affected first.
Fe-deficiency symptoms and effects on growth
Interveinal yellowing and chlorosis of emerging leaves
(Annex A-11, A-29).
Soil
Fe deficiency is likely when soil Fe concentration is either
4 2 mg Fe per kg: NH4
-acetate, pH 4.8, or
4 4–5 mg Fe per kg: DTPA-CaCl2
, pH 7.3.
Causes of Fe deficiency
4 Low concentration of soluble Fe2+
in upland soils.
4 Insufficient soil reduction under submerged conditions (e.g.,
low organic matter status soils).
4 High pH of alkaline or calcareous soils following
submergence (i.e., decreased solubility and uptake of Fe
because of large bicarbonate concentrations).
4 Wide P:Fe ratio in the soil (i.e., Fe bound in Fe phosphates,
possibly because of the excessive application of P fertilizer).
Occurrence of Fe deficiency
4 Neutral, calcareous, and alkaline upland soils.
4 Alkaline and calcareous lowland soils with low organic
matter status.
4 Lowland soils irrigated with alkaline irrigation water.
4 Coarse-textured soils derived from granite.

66
Effect of submergence on Fe availability and uptake
Fe availability increases after flooding. Solubility of Fe
increases when Fe3+
is reduced to the more soluble Fe2+
during organic matter decomposition. In flooded soils, Fe
deficiency may occur when organic matter decomposition is
insufficient to drive the reduction of Fe3+
to Fe2+
.
Preventive strategies for Fe management
4 Varieties: Selection of high-Fe rice cultivars is in progress to
improve human Fe nutrition.
4 Soil management: Apply organic matter (e.g., crop residues,
animal manure).
4 Fertilizer management: Use acidifying fertilizers (e.g.,
ammonium sulfate instead of urea) on high-pH soils. Use
fertilizers containing Fe as a trace element.
Treatment of Fe deficiency
Fe deficiency is the most difficult and costly micronutrient
deficiency to correct. Soil applications of inorganic Fe
sources are often ineffective in controlling Fe deficiency,
except when application rates are large. Fe deficiency
should be treated as follows:
4 Apply solid FeSO4
(about 30 kg Fe per ha) next to rice rows,
or broadcast (larger application rate required).
4 Foliar applications of FeSO4
(2–3% solution) or Fe chelates.
Because of low Fe mobility in the plant, 2–3 applications
at 2-week intervals (starting at tillering) are necessary to
support new plant growth.

67
2.10 Manganese deficiency
Function and mobility of Mn
Manganese is required for photosynthesis. Mn accumulates
in roots before it moves to aboveground shoots. There is
some translocation of Mn from old to young leaves.
Mn-deficiency symptoms and effects on growth
Interveinal chlorosis starting at the tip of younger leaves
(Annex A-11, A-31).
Soil
Critical soil levels for occurrence of Mn deficiency:
4 1 mg Mn per kg, terephthalic acid + CaCl2
, pH 7.3.
4 12 mg Mn per kg, 1N NH4
-acetate + 0.2% hydroquinone,
pH 7.
Causes of Mn deficiency
4 Small available Mn content in soil.
4 Fe-induced Mn deficiency because of a large concentration
of Fe in soil.
4 Reduced Mn uptake because of large concentrations of
Ca2+
, Mg2+
, Zn2+
, or NH4
+
in soil solution.
4 Excessive liming of acid soils.
4 Reduced Mn uptake because of hydrogen sulfide
accumulation.
Occurrence of Mn deficiency
Mn deficiency occurs frequently in upland rice, but is
uncommon in rainfed or lowland rice because the solubility
of Mn increases under submerged conditions.

68
Soils particularly prone to Mn deficiency
4 Acid upland soils (Ultisols, Oxisols).
4 Alkaline and calcareous soils with low organic matter status
and small amounts of reducible Mn.
4 Degraded paddy soils containing large amounts of active
Fe.
4 Leached, sandy soils containing small amounts of Mn.
4 Alkaline and calcareous organic soils (Histosols).
4 Highly weathered soils with low total Mn content.
Effect of submergence on Mn availability and uptake
Mn availability increases with flooding as Mn4+
is reduced to
the more plant-available Mn2+
.
Preventive strategies for Mn management
4 Crop management: Apply farmyard manure or straw
(incorporated or burned).
4 Fertilizer management: Use acid-forming fertilizers, such as
ammonia sulfate, (NH4
)2
SO4
, instead of urea.
Treatment of Mn deficiency
Mn deficiencies can be corrected by foliar application of
Mn or by banding Mn with an acidifying starter fertilizer. Mn
deficiency should be treated as follows:
4 Apply MnSO4
or finely ground MnO (5–20 kg Mn per ha) in
bands along rice rows.
4 Apply foliar MnSO4
for rapid treatment of Mn deficiency (1–5
kg Mn per ha in about 200 L water per ha).
4 Chelates are less effective because Fe and Cu displace Mn.

69
2.11 Copper deficiency
Function and mobility of Cu
Copper plays a key role in the following processes:
4 N, protein, and hormone metabolism.
4 Photosynthesis and respiration.
4 Pollen formation and fertilization.
The mobility of Cu in rice plants depends partly on leaf
N status; little retranslocation of Cu occurs in N-deficient
plants. Cu-deficiency symptoms are more common on
young leaves.
Cu-deficiency symptoms and effects on growth
Chlorotic streaks, bluish green leaves, which become
chlorotic near the tips (Annex A-11, A-33).
Soil
Critical soil levels for occurrence of Cu deficiency:
4 0.1 mg Cu per kg, 0.05N HCl, or
4 0.2–0.3 mg Cu per kg, DTPA + CaCl2
, pH 7.3.
Causes of Cu deficiency
4 Small amount of available Cu in soil.
4 Strong adsorption of Cu on humic and fulvic acids (peat
soils).
4 Small amounts of Cu in parent materials (sandy soils
derived from quartz).
4 Large NPK fertilizer application rates, resulting in rapid plant
growth rates and exhaustion of Cu in soil solution.
4 Overliming of acid soils.
4 Excessive Zn in the soil, inhibiting Cu uptake.

70
Occurrence of Cu deficiency
4 High organic matter status soils (Histosols, humic volcanic
ash soils, peat soils).
4 Lateritic, highly weathered soils (Ultisols, Oxisols).
4 Soils derived from marine sediments (limestone).
4 Sandy-textured soils, calcareous soils.
Effect of submergence on Cu availability and uptake
The availability of Cu decreases at flooding.
Preventive strategies for Cu management
4 Crop management: Dip seedling roots in 1% CuSO4
suspensions for an hour before transplanting.
4 Soil management: Avoid overliming of acid soils because it
may reduce Cu uptake.
4 Fertilizer management: On Cu-deficient soils, apply CuO or
CuSO4
(5–10 kg Cu per ha at 5-year intervals) for long-term
maintenance of soil Cu (broadcast and incorporate in soil).
Treatment of Cu deficiency
4 Apply CuSO4
(solid or liquid form) for rapid treatment of Cu
deficiency (about 1–5 kg Cu per ha). For soil application,
fine CuSO4
material is either broadcast (or banded) on the
soil or incorporated as a basal application.
4 Foliar Cu can be applied during tillering to panicle initiation,
but may cause leaf burn in growing tissues.
4 Avoid applying excessive Cu because the range between
Cu deficiency and toxicity is narrow.

71
2.12 Boron deficiency
Function and mobility of B
Boron is an important constituent of cell walls. B deficiency
results in reduced pollen viability.
Because B is not retranslocated to new growth, deficiency
symptoms usually appear first on young leaves.
B-deficiency symptoms and effects on growth
White, rolled leaf tips of young leaves (Annex A-11).
Soil
The critical soil level for occurrence of B deficiency is 0.5
mg B per kg hot water extraction.
Causes of B deficiency
4 Small amount of available B in soil.
4 B adsorption on organic matter, clay minerals, and
sequioxides.
4 Reduction in B mobility because of drought.
4 Excessive liming.
Occurrence of B deficiency
4 Highly weathered, acid red soils and sandy rice soils.
4 Acid soils derived from igneous rocks.
4 High organic matter status soils.
Effect of submergence on B availability and uptake
When pH6, B is present mostly as undissociated boric
acid, B(OH)3
, and plant uptake depends on mass flow.
When pH6, B(OH)3
is increasingly dissociated and
hydrated to B(OH)4
-
and uptake is actively regulated by

72
the plant. B adsorption to organic matter, sequioxides, and
clay minerals increases with increasing pH. Therefore, after
flooding, B availability decreases in acid soils and increases
in alkaline soils.
Preventive strategies for B management
4 Water management: Avoid excessive leaching (percolation).
B is very mobile in flooded rice soils.
4 Fertilizer management: On B-deficient soils, apply slow-
acting B sources (e.g., colemanite) at intervals of 2–3 years.
Treatment of B deficiency
4 Apply B in soluble forms (borax) for rapid treatment of B
deficiency (0.5–3 kg B per ha), broadcast and incorporated
before planting, topdressed, or as foliar spray during
vegetative rice growth.
4 Borax and fertilizer borates should not be mixed with
ammonium fertilizers as this will cause NH3
volatilization.

73
2.13 Iron toxicity
Mechanism of Fe toxicity
Iron toxicity is primarily caused by the toxic effects of
excessive Fe uptake because of a large concentration of
Fe in the soil solution. Recently transplanted rice seedlings
may be affected when large amounts of Fe2+
accumulate
immediately after flooding. In later growth stages, rice plants
are affected by excessive Fe2+
uptake because of increased
root permeability and enhanced microbial Fe reduction in the
rhizosphere. Excessive Fe uptake results in leaf bronzing.
Large amounts of Fe in plants can cause phytotoxicity. Fe
toxicity is related to multiple nutritional stress, which leads to
reduced root oxidation power. A black stain of Fe sulfide (a
diagnostic indication of excessively reduced conditions and
Fe toxicity) may then form on the root surface.
Fe-toxicity symptoms and effects on growth
Tiny brown spots on lower leaves starting from the tip or
whole leaves colored orange-yellow to brown. Black coating
on root surfaces (Annex A-35).
Plant
Fe content in affected plants is usually (but not always)
high (300–2,000 mg Fe per kg), but the critical Fe content
depends on plant age and general nutritional status. The
critical threshold is lower in low fertility status soils in which
nutrient supply is not properly balanced.
Effect of submergence on Fe toxicity
In most mineral soils, the concentration of Fe2+
peaks at
2–4 weeks following submergence. A large concentration of
Fe2+
in the soil may retard K and P uptake. Under strongly
reducing conditions, the production of H2
S and FeS may

74
contribute to Fe toxicity by reducing root oxidation power.
The oxidation of Fe2+
to Fe3+
because of the release of oxygen
by rice roots causes acidification in the rice rhizosphere and
the formation of a brownish coating on rice roots.
Causes of Fe toxicity
4 A large Fe2+
concentration in the soil solution because of
strongly reducing conditions in the soil and/or low pH.
4 Low and unbalanced crop nutrient status. Poor root
oxidation and Fe2+
exclusion power because of P, Ca, Mg,
or K deficiency.
4 Poor Fe2+
exclusion power because of the accumulation in
the rhizosphere of substances that inhibit respiration, such
as organic acids, H2
S, and FeS (Section 2.14).
4 Application of large amounts of undecomposed organic
residues.
4 Continuous supply of Fe into soil from groundwater or
lateral seepage from hills.
4 Application of urban or industrial sewage with a high Fe content.
Occurrence of Fe toxicity
Fe toxicity occurs on a wide range of soils, but generally
in lowland rice soils with permanent flooding during crop
growth. Common features of Fe-toxic sites are poor
drainage and low soil CEC and macronutrient content, but
Fe toxicity occurs over a wide range of soil pH (4–7). Soils
prone to Fe toxicity are
4 Poorly drained soils (Aquents, Aquepts, Aquults) in inland
valleys receiving inflow from acid upland soils.
4 Kaolinitic soils with low CEC and little available P and K.
4 Alluvial or colluvial acid clayey soils.
4 Young acid-sulfate soils.
4 Acid lowland or highland peat soils.

75
Preventive strategies for Fe toxicity management
4 Varieties: Plant rice varieties tolerant of Fe toxicity (e.g.,
IR8192-200, IR9764-45, Kuatik Putih, Mahsuri).
4 Seed treatment: In temperate climates where direct seeding
is practiced, coat seeds with oxidants (e.g., Ca peroxide
at 50–100% of seed weight) to improve germination and
seedling emergence by increasing the O2
supply.
4 Crop management: Delay planting until the peak in Fe2+
concentration has passed (i.e., not less than 10–20 days
after flooding).
4 Water management: Use intermittent irrigation and avoid
continuous flooding on poorly drained soils containing a
large concentration of Fe and organic matter.
4 Fertilizer management: Balance the use of fertilizers (NPK
or NPK + lime) to avoid nutrient stress. Apply lime on acid
soils. Do not apply excessive amounts of organic matter
(manure, straw) on soils containing large amounts of Fe and
organic matter or where drainage is poor.
4 Soil management: Carry out dry tillage after the rice harvest
to increase Fe oxidation during the fallow period.
Treatment of Fe toxicity
Preventive management strategies should be followed
because treatment of Fe toxicity during crop growth is
difficult. Options for treatment of Fe toxicity:
4 Apply additional K, P, and Mg fertilizers.
4 Incorporate lime in the topsoil to raise pH in acid soils.
4 Incorporate about 100–200 kg MnO2
per ha in the topsoil to
decrease Fe3+
reduction.
4 Carry out midseason drainage to remove accumulated Fe2+
.
At the midtillering stage (25–30 DAT/DAS), drain the field
and keep it free of floodwater (but moist) for about 7–10
days to improve oxygen supply during tillering.

76
2.14 Sulfide toxicity
Mechanism of sulfide toxicity
An excessive concentration of hydrogen sulfide in the soil
results in reduced nutrient uptake because of a decrease in
root respiration. Hydrogen sulfide has an adverse effect on
metabolism when an excessive amount is taken up by the
rice plant.
Rice roots release O2
to oxidize H2
S in the rhizosphere. H2
S
toxicity therefore depends on the strength of root oxidizing
power, H2
S concentration in the soil solution, and root health
as affected by nutrient supply. Young rice plants are particularly
susceptible to sulfide toxicity before the development
of oxidizing conditions in the rhizosphere. Physiological
disorders attributed to H2
S toxicity include Akiochi in Japan
and straighthead in the southern United States.
Sulfide-toxicity symptoms and effects on growth
Interveinal chlorosis of emerging leaves. Coarse, sparse,
and blackened roots (Annex A-37).
Leaf symptoms of sulfide toxicity are similar to those of
chlorosis caused by Fe deficiency (Section 2.9). Other
diagnostic criteria are similar to those of Fe toxicity (but
Fe toxicity has different visual leaf deficiency symptoms,
Section 2.13):
4 Coarse, sparse, dark brown to black root system. Freshly
uprooted rice hills often have poorly developed root systems
with many black roots (stains of Fe sulfide). In contrast,
healthy roots are covered with a uniform and smooth
orange-brown coating of Fe3+
oxides and hydroxides.
4 Small concentration of K, Mg, Ca, Mn, and Si content in
plant tissue.

77
Normal ranges and critical levels for occurrence of
sulfide toxicity
No critical levels have been established. Sulfide toxicity
depends on the concentration of sulfide in the soil solution
relative to the oxidation power of rice roots. H2
S toxicity can
occur when the concentration of H2
S is 0.07 mg per L in the
soil solution.
Effect of submergence on sulfide toxicity
The reduction of sulfate to sulfide in flooded soils has three
implications for rice culture:
4 S may become deficient,
4 Fe, Zn, and Cu may become immobilized, and
4 H2
S toxicity may occur in soils containing small amounts of Fe.
In submerged soils, sulfate is reduced to H2
S at low redox
potential (-50 mV at pH 7), which then forms insoluble
sulfides such as FeS.
Fe sulfides are not toxic to rice, but they reduce nutrient
uptake (Section 2.13).
Causes of sulfide toxicity
4 A large concentration of H2
S in the soil solution (because of
strongly reducing conditions and little precipitation of FeS).
4 Poor and unbalanced crop nutrient status, causing reduced
root oxidation power (because of deficiencies of K in
particular but also of P, Ca, or Mg).
4 Excessive application of sulfate in fertilizers or urban or
industrial sewage on poorly drained, strongly reducing soils.
Soils prone to H2
S toxicity
4 Well-drained sandy soils with low active Fe status.
4 Degraded paddy soils with low active Fe status.
4 Poorly drained organic soils.

78
4 Acid-sulfate soils.
Soils prone to sulfide toxicity and Fe toxicity are similar in
containing a large amount of active Fe, small CEC, and
small concentration of exchangeable bases.
Preventive strategies for sulfide toxicity
management
4 Varieties: Grow rice varieties that tolerate sulfide toxicity
because of their greater capacity to release O2
from roots.
4 Seed treatment: In temperate climates, coat seeds with
oxidants (e.g., Ca peroxide) to increase the O2
supply at
seed germination.
4 Water management: Avoid continuous flooding and use
intermittent irrigation in soils that contain large concentrations
of S, have high organic matter status, and are poorly
drained.
4 Fertilizer management: Balance the use of fertilizer nutrients
(NPK or NPK + lime) to avoid nutrient stress and improve
root oxidation power. Apply sufficient K fertilizer (Section
2.3). Avoid using excessive amounts of organic residues
(manure, straw) in soils containing large amounts of Fe and
organic matter, and in poorly drained soils.
4 Soil management: Carry out dry tillage after harvest to
increase S and Fe oxidation during the fallow period.
Treatment of sulfide toxicity
4 Apply K, P, and Mg fertilizers.
4 Apply Fe (salts, oxides) on low-Fe soils to increase
immobilization of H2
S as FeS.
4 Carry out midseason drainage to remove accumulated H2
S
and Fe2+
. Drain the field at the midtillering stage (25–30
DAT/DAS), and maintain floodwater-free (but moist) conditions
for about 7–10 days to improve oxygen supply during tillering.

79
2.15 Boron toxicity
Mechanism of B toxicity
When the B concentration in the soil solution is large, B is
distributed throughout the plant following water movement
driven by transpiration, causing the accumulation of B in
leaf margins and leaf tips. Excess B appears to inhibit the
formation of starch from sugars or results in the formation of
B-carbohydrate complexes, resulting in retarded grain filling
but normal vegetative growth.
B-toxicity symptoms and effects on growth
Brownish leaf tips and dark brown elliptical spots on leaves
(Annex A-39).
Plant
4 There is a steep concentration gradient of B within a leaf blade,
from low values at the leaf base to high values at the leaf tip.
4 Critical toxicity levels in field-grown rice are lower than those
of plants grown in the greenhouse because B is leached
from leaves under open conditions during rainfall.
4 The effect on yield differs significantly among rice varieties.
Soil
Critical toxicity limits of B in the soil:
4 4 mg B per kg: 0.05N HCl.
4 5 mg B per kg: hot-water soluble B.
4 2.5 mg B per L: soil solution.
Irrigation water
B concentration of 2 mg B per L may cause B toxicity.
Effect of submergence on B toxicity
4 Flooding acid soils decreases B availability.

80
4 Flooding alkaline soils increases B availability.
Causes of B toxicity
4 A large B concentration in the soil solution because of the use
of B-rich groundwater and high temperature.
4 A large B concentration in the soil solution because of
B-rich parent material. B content is large in some marine
sediments, plutonic rocks, and other volcanic materials.
4 Excess application of borax or municipal waste.
Occurrence of B toxicity
B toxicity is most common in arid and semiarid regions, but
has also been reported in rice in other areas.
Soils prone to B toxicity
4 Soils formed on volcanic parent material, usually associated
with the use of irrigation water pumped from deep wells
containing a large B concentration.
4 Some coastal saline soils.
Preventive strategies for B toxicity management
4 Varieties: Plant B-toxicity-tolerant varieties (e.g., IR42, IR46,
IR48, IR54, IR9884-54).
4 Water management: Use surface water with a low B content
for irrigation. Groundwater must be monitored regularly if
used for irrigation. If the B concentration is too great, dilute
with uncontaminated water.
4 Soil management: Plow when the soil is dry so that B
accumulates in the topsoil. Then leach with water containing
a small amount of B.
Treatment of B toxicity
Leach with low-B irrigation water if percolation is sufficient
and a suitable water source is available.

81
2.16 Manganese toxicity
Mechanism of Mn toxicity
Manganese concentration in the soil solution can increase at
low soil pH or when the redox potential is low after flooding.
Excessive amounts of Mn in the soil solution can lead to
excess Mn uptake when exclusion or tolerance mechanisms
in roots are not functioning adequately. A large concentration
of Mn in plant tissue changes metabolic processes (e.g.,
enzyme activities and organic compounds) that lead to
visible Mn-toxicity symptoms such as chlorosis or necrosis.
Mn-toxicity symptoms and effects on growth
Yellowish brown spots between leaf veins, extending to the
whole interveinal area (Annex A-41).
Effect of submergence on Mn toxicity
Flooding affects Mn toxicity in rice because of
4 Increased Mn solubility with decreasing redox potential.
4 Reduced Mn oxidation by roots because of a lack of oxygen.
Causes of Mn toxicity
Mn toxicity can be caused by
4 A large concentration of Mn2+
in the soil solution because of
low soil pH (5.5) and/or low redox potential.
4 Poor and unbalanced crop nutrient status.
4 Poor root oxidation and Fe2+
‑excluding power because of
8 deficiencies of Si, K, P, Ca, or Mg, and
8 substances that inhibit respiration (e.g., organic acids,
H2
S, and FeS) (Section 2.14).
4 Application of urban or industrial waste with large Mn content.

82
Occurrence of Mn toxicity
Mn toxicity rarely occurs in lowland rice. Despite large Mn
concentrations in solution, Mn toxicity is uncommon because
rice is comparatively tolerant of large Mn concentrations.
Rice roots are able to exclude Mn and rice has a high
internal tolerance for large tissue-Mn concentrations. Soils
where Mn toxicity can occur are as follows:
4 Acid, upland soils (pH5.5), in which Mn toxicity often occurs
together with Al toxicity (Section 2.17); lowland soils containing
large amounts of easily reducible Mn; and acid-sulfate soils.
4 Areas affected by Mn mining (e.g., Japan).
Preventive strategies for Mn toxicity management
4 Seed treatment: In a temperate climate, coat seeds with
oxidants (e.g., Ca peroxide) to improve germination and
seedling emergence by increasing the supply of O2
.
4 Water management: Mn absorption may be increased when
surface drainage is practiced.
4 Fertilizer management: Balance the use of fertilizers (NPK or
NPK + lime) to avoid nutrient stress as a source of Mn toxicity.
Apply lime on acid soils to reduce the concentration of active
Mn. Do not apply excessive amounts of organic matter
(manure, straw) on soils containing large concentrations of
Mn and organic matter, and on poorly drained soils.
4 Straw management: Recycle straw or ash to replenish Si and
K removed from the field. An adequate Si supply prevents
Mn toxicity of rice plants by decreasing plant Mn uptake
(increased root oxidation) and by increasing the internal
tolerance for an excessive amount of Mn in plant tissue.
Treatment of Mn toxicity
4 Apply lime to alleviate soil acidity in upland soils.
4 Apply silica slags (1.5–3 t/ha) to alleviate Si deficiency
(Section 2.6).

83
2.17 Aluminum toxicity
Mechanism of Al toxicity
The most important symptom of Al toxicity is the inhibition of
root growth. Long-term exposure of plants to Al also inhibits
shoot growth by inducing nutrient (Mg, Ca, P) deficiencies
and drought stress.
Al-toxicity symptoms and effects on growth
Orange-yellow interveinal chlorosis on leaves. Poor root
growth, stunted plants (Annex A-43).
Soil
Al saturation of 30%, soil pH (H2
O) 5.0, and 1–2 mg Al
per L in the soil solution indicate potential Al toxicity.
Effect of submergence on Al toxicity
Al toxicity is a major constraint in upland soils under aerobic
and acid soil conditions. Upon flooding, soil pH increases
and Al concentration in the soil solution decreases and
generally falls below the critical level for Al toxicity. Under
such conditions, Fe toxicity (Section 2.13) is more likely to
occur than Al toxicity.
Causes of Al toxicity
Excess Al3+
concentration in the soil solution is caused by
low soil pH (5). The concentration of Al in the soil solution
depends on soil pH as well as the concentration of organic
and inorganic compounds that can form complexes with Al.
Occurrence of Al toxicity
Al toxicity rarely occurs in lowland rice except in some soils
where soil reduction after flooding proceeds very slowly. Al
toxicity occurs on the following soils:

84
4 acid, upland soils (Ultisols, Oxisols) with large exchangeable
Al content. Al toxicity often occurs together with Mn toxicity
(Section 2.16);
4 acid-sulfate soils, particularly when rice is grown as an
upland crop for a few weeks before flooding; and
4 flooded soils with pH4 before Fe-toxicity symptoms appear.
Preventive strategies for Al-toxicity management
4 Varieties: Plant Al-tolerant cultivars, such as IR43, CO
37, and Basmati 370 (India), Agulha Arroz, Vermelho,
and IAC3 (Brazil), IRAT 109 (Côte d’Ivoire), and Dinorado
(Philippines).
4 Crop management: Delay planting until pH has increased
sufficiently after flooding (to immobilize Al).
4 Water management: Provide crops with sufficient water to
maintain reduced soil conditions. Prevent the topsoil from
drying out.
4 Fertilizer management: On acid upland soils with Al toxicity,
pay special attention to Mg fertilization (Section 2.7). Liming
with CaCO3
may not be sufficient, whereas the application
of dolomite instead of CaCO3
not only raises the pH but also
supplies Mg. Small amounts of kieserite and langbeinite (50
kg per ha) may have an effect similar to that of liming with
more than 1,000 kg CaCO3
.
Treatment of Al toxicity
4 Apply 1–3 t lime per ha to raise pH.
4 Ameliorate subsoil acidity to improve root growth below the
plow layer by leaching Ca into the subsoil from lime applied
to the soil surface.
4 On acid, upland soils, install soil erosion traps and
incorporate 1 t/ha of reactive rock phosphate to alleviate P
deficiency (Section 2.2).

85
2.18 Salinity
Mechanism of salinity injury
Salinity is defined as the presence of excessive amounts of
soluble salts in the soil. Na, Ca, Mg, chloride, and sulfate
are the major ions involved. The effects of salinity on rice
growth are
4 osmotic effects (water stress),
4 toxic ionic effects of excess Na and Cl uptake, and
4 a reduction in nutrient uptake (K, Ca) because of
antagonistic effects.
Rice tolerates salinity during germination, is very sensitive
during early growth (1–2-leaf stage), is tolerant during
tillering and elongation, but becomes sensitive again at
flowering.
Salinity symptoms and effects on growth
White leaf tips and stunted, patchy growth in the field
(Annex A-45).
Further effects on rice growth include
4 reduced germination rate,
4 reduced plant height and tillering,
4 poor root growth, and
4 increased spikelet sterility.
Soil
For rice growing in flooded soil, EC is measured in the soil
solution or in a saturation extract (ECe
). For upland rice
grown at field capacity or below, EC in the soil solution is
about twice as great as that of the saturation extract. Rough
approximations of the yield decrease caused by salinity are

86
4 ECe
2 dS/m: optimum, no yield reduction
4 ECe
4 dS/m: slight yield reduction (10–15%)
4 ECe
6 dS/m: moderate reduction in growth and yield
(20–50%)
4 ECe
10 dS/m: 50% yield reduction in susceptible cultivars
Exchangeable sodium percentage (ESP):
4 ESP 20%: no significant yield reduction
4 ESP 20–40%: slight yield reduction (10%)
4 ESP 80%: 50% yield reduction
Sodium adsorption ratio (SAR):
4 SAR 15: sodic soil (measured as cations in saturation
extract)
Irrigation water
4 pH 6.5–8, EC 0.5 dS/m: high quality
4 pH 8–8.4, EC 0.5–2 dS/m: medium-to-poor
4 pH 8.4, EC 2 dS/m: unsuitable for irrigation
4 SAR 15: high quality, low Na
4 SAR 15–25: medium-to-poor quality, high Na
4 SAR 25: unsuitable for irrigation, very high Na
Effect of submergence on salinity
Submergence has two effects on salinity:
4 An increase in EC because of the greater solubility of salts
and the reduction of Fe and Mn from less soluble to soluble
compounds.
4 Continuous percolation of the soil because of irrigation.
If the EC in the irrigation water exceeds that of the soil
solution, the concentration of salt in the soil will increase.

87
Causes of salinity
Plant growth on saline soils is mainly affected by high levels
of soluble salts (NaCl) causing ion toxicity, ionic imbalance,
and impaired water balance. On sodic soils, plant growth is
mainly affected by high pH and high HCO3
-
concentration.
Major causes of salinity or sodicity:
4 Poor irrigation practice or insufficient irrigation water in
seasons/years with low rainfall.
4 High evaporation.
4 An increase in the level of salinity in groundwater.
4 Intrusion of saline seawater in coastal areas.
Occurrence of salinity
Salt-affected soils can be grouped into
4 saline soils (EC 4 dS/m, ESP 15%, pH 8.5),
4 saline-sodic soils (EC 4 dS/m, ESP 15%, pH about 8.5),
and
4 sodic soils (EC 4 dS/m, ESP 15%, pH 8.5, SAR 15).
Examples of salt-affected soils include
4 saline coastal soils (widespread along coasts in many
countries),
4 saline acid-sulfate soils (e.g., Mekong Delta, Vietnam),
4 neutral to alkaline saline, saline-sodic, and sodic inland soils
(e.g., India, Pakistan, Bangladesh), and
4 acid sandy saline soils (Korat region of northeast Thailand).
Preventive strategies for salinity management
Management of salinity or sodicity must include a
combination of measures. Major choices include the
following:

88
4 Cropping system: In rice-upland crop systems, change
to double-rice cropping if sufficient water is available and
climate allows. After a saline soil is leached, a cropping
pattern that includes rice and other salt-tolerant crops (e.g.,
legumes such as clover or Sesbania) must be followed for
several years.
4 Varieties: Grow salt-tolerant varieties (e.g., Pobbeli,
Indonesia; IR2151, Vietnam; AC69-1, Sri Lanka; IR6,
Pakistan; CSR10, India; Bicol, Philippines).
4 Water management: Submerge the field for 2–4 weeks
before planting rice. Do not use sodic irrigation water or
alternate between sodic and nonsodic irrigation water
sources. Leach the soil after planting under intermittent
submergence to remove excess salts. Collect and store
rainwater for irrigation of dry-season crops (e.g., by
establishing reservoirs). In coastal areas, prevent intrusion
of salt water.
4 Fertilizer management: Apply Zn (5–10 kg Zn per ha) to
alleviate Zn deficiency (Section 2.4). Apply sufficient N,
P, and K. The application of K (Section 2.3) is important
because it improves the K:Na, K:Mg, and K:Ca ratios in the
plant. Use ammonium sulfate as an N source and apply
N as topdressing at critical growth stages (Section 2.1)
(basal N is less efficient on saline and sodic soils). In sodic
soils, the replacement of Na by Ca (through the application
of gypsum) may reduce P availability and result in an
increased requirement for P fertilizer.
4 Organic matter management: Organic amendments
facilitate the reclamation of sodic soils by increasing partial
CO2
pressure and decreasing pH. Apply rice straw to
recycle K. Apply farmyard manure.

89
Treatment of salinity
Options for treatment of salinity:
4 Saline soils: Salinity can only be reduced by leaching with
salt-free irrigation water. Because rice has a shallow root
system, only the topsoil (0–20 cm) needs to be leached.
Cost, availability of suitable water, and soil physical
and hydraulic characteristics determine the feasibility of
leaching. To reduce the level of salinity in affected soils,
electrical conductivity in the irrigation water should be 0.5
dS/m). Where high-quality surface water is used (EC about
0), the amount of water required to reduce a given ECe
to a
critical-level ECc
can be calculated as follows:
Aiw
= Asat
[(ECe
/ECc
) + 1]
where Aiw
represents the amount of irrigation water (cm)
added during irrigation and Asat
is the amount of water (cm)
in the soil under saturated conditions.
For example, to lower an initial ECe
of 16 dS/m to 4 dS/m
in the top 20 cm of a clay loam soil (Asat
= 8–9 cm), about
40 cm of fresh water is required. Subsurface drains are
required for leaching salts from clay-textured soils.
4 Sodic soils: Apply gypsum (CaSO4
) to reduce Na saturation
of the soil.
Make a foliar application of K at the late tillering and panicle
initiation stages, particularly if a low-tolerance variety is
grown on saline soil.

A-
Field management of rice
High-quality crop management is essential to derive maximum benefit
from site-specific management.
Photo captions
(a) Proper leveling reduces water requirements and ensures even
growth during early growth stages.
(b) Good-quality seeds with a high germination rate reduce seed
requirements and result in strong, healthy seedlings.
(c) In transplanted rice, optimal seedling age is about 14–18 d with 1–2
seedlings per hill, whereas older seedlings of ≥21 days may require 2–3
seedlings per hill.
(d) Optimal canopy development is only reached with adequate planting
density, with hills spaced 16–23 cm apart in transplanted rice, and
80–120 kg seeds per ha in broadcast wet-seeded rice.
(e) Weeds compete with rice plants for space, water, and nutrients and
thus reduce yield.
(f) Observation of pests and diseases saves money, as pesticide
application can be reduced with integrated pest management.
(g) Lodging can be avoided with well-timed N management using the
leaf color chart to synchronize N supply with crop demand and balanced
nutrient management, thus increasing plant strength and resistance to
lodging.
(h) The right harvesting time to achieve the highest yield is at full
maturity, when grains are hard and fully filled.

Nutrient Deficiency A-
(b)
(e)
(c)
(a)
(d)
(f)
(g) (h)

A-
Nutrient management tools: omission plots
Soil indigenous nutrient supply of N, P, and K can be measured from
grain yield in 0 N, 0 P, and 0 K omission plots, respectively.
Photo captions
(a) Install omission plots (5 × 5-m size) at the long side of the field, not
in a corner.
(b) Construct bunds of 25-cm height to avoid fertilizer contamination.
(c) Double bunds effectively reduce fertilizer contamination and bunds
need to be well maintained throughout the season.
(d) Irrigation is ideally performed for individual plots, avoiding water
running through all plots, which may cause fertilizer contamination.
(e) A well-established 0 N plot in a farmer’s field at midseason.
(f) Sufficient and well-timed fertilizer N topdressing is important in 0 P
and 0 K plots to make sure that N is not limiting growth.
(g) Excellent omission plot with a pronounced difference in growth when
compared with the adjoining farmer’s field.
(h) At full maturity, harvest all plants from a central 5-m2
area and avoid
plants from border rows. Carefully remove all grain from the spikelets,
then dry and weigh the grain.

(a) (b)
(c) (d)
(e) (f)
(g) (h)

A-
Nutrient management tools: leaf color chart (LCC)
The timing of fertilizer N application during the cropping season can be
improved by assessing plant N status using the LCC.
Note: The panels of the new, standardized 4-panel LCC are numbered 2,
3, 4, and 5, so that the critical values correspond to those used with the
older LCCs.
For the standardized IRRI LCC with most rice varieties, the leaf colors
mentioned in Tables 7–9 correspond to LCC values as follows:
4 Yellowish green = LCC value 3,
4 Intermediate = LCC value 3.5 (intermediate between 3 and 4), and
4 Green = LCC value 4.
Photo captions
(a) Plants look N-deficient in this field without fertilizer application.
(b) This was confirmed through an LCC measurement, since leaves were
yellowish with a color between panels 2 and 3.
(c), (d) At low fertilizer N rates, plant appearance is better, but the low
LCC reading still indicates N deficiency.
(e), (f) Plants look well developed and the canopy is closed at the higher
fertilizer N rates, while the LCC reading is between panels 3 and 4, which
is in most cases the critical value for transplanted rice. With real-time N
management, fertilizer N should typically be applied soon when leaf color
drops below 3.5 for transplanted rice and 3 for wet-seeded rice. With
fixed-time N management, a relatively higher rate of fertilizer N should be
applied when leaf color drops near 3 for transplanted rice and below 3 for
wet-seeded rice.
(g), (h) Plants look very dark at the very high N rate. Leaf color is very
dark green and darker than LCC panel no. 4 indicating no N deficiency.

(c)
(a)
(e)
(g)
(d)
(b)
(h)
(f)
2 3 4 5LCC panels:

A-
Growth stages
Extension workers and farmers should work together to identify the local
names for the most important growth stages of rice to organize fertilizer
application at the right time.
Photo captions
The duration of the vegetative phase differs with variety and may range
from 30 to 80 d for modern high-yielding varieties. The duration of the
reproductive and ripening phases is, at 30–35 d, about the same for most
varieties. Using the leaf color chart, most fertilizer N should be applied
in 2–4 split applications between early tillering and panicle initiation.
In high-yielding seasons or in hybrid rice, a late N application could be
given at heading to first flowering. Flowering to harvest takes about 30
days. Thus, sowing to harvest may range from 90 to 160 days in irrigated
rice, depending on variety.

SeedlingTrans-
planting
Panicle
initiation
FloweringHarvest
Growth
stage
Duration
Maximum
tiller
number
VegetativephaseRipeningphaseReproductivephase
Variable30days35days
A-9

A-10
Diagnostic key for identifying nutrient deficiencies in ricetsrifsevaelredlonodezilacoLtsrifsevaelregnuoynodezilacoL
,neergthgiL
trohs,worran
sevael
,neergkraD
tcere,worran
sevael
kradotneerG
sevaelneerg
-citorolhC
faelcitorcen
snigram
nworbytsuR
stopscitorcen
dnaneerG
sepirtswolley
gninnur
lellarap
gnillorfaeL
wolley-egnarO
lanievretni
,sisorolhc
yhctap
llarevoelaP
roloc
neerG
gniroloc
sniamer
on(yhctap
)sepirts
ypoord,tfoS
dnasevael
smluc
,neergthgiL
sevaelelap
citorolhC
sevaelreppu
tnalpelohW
tub,detceffa
sevaelreppu
tsrifdetceffa
stnalpdetnutS
gnirellitrooP
stnalpdetnutS
gnirellitrooP
stnalpretrohSstnalpdetnutS
gnirellitrooP
stnalpdetnutS
gnirellitdecudeR
dleifelohW
sraeppa
hsiwolley
ytirutamylraE
deyaleD
ytirutam
gnitliwylraE
ytirutamdna
tooryhtlaehnU
metsys
desaercnI
foecnedicni
sesaesid
tooryhtlaehnU
metsys
,nevenU
dleifyhctap
htworg
deyaleD
ytirutam
NPKgMnZS

Nutrient Deficiency A-11
Diagnostic key for identifying nutrient deficiencies in rice
tsrifsevaelregnuoynodezilacoL
dezilacoltoN
smotpmys
-citorolhC
rotilpscitorcen
spitfaeldellor
smotpmyS
ylnoelbisiv
erevesrednu
ycneicifed
lanievretnI
dnagniwolley
fosisorolhc
gnigreme
sevael
decudeR
llyhporolhc
nitnetnoc
sevael
eritne,retaL
sevael
rocitorolhc
hsitihw
hsiyargelaP
neerg
lanievretni
tasisorolhc
fopiteht
sevaelgnuoy
citorceN
gnittops
citorolhC
skaerts
neerghsiulB
sevael
gnuoygnitliW
sevael
dellor,etihW
fospitfael
sevaelgnuoy
fohtaeD
fitniophtworg
ereves
ypoord,tfoS
sevael
stnalpretrohSdecudeR
gnirellit
tnalpdecudeR
thgieh
tooryhtlaehnU
metsys
nieraryreV
ecirdetagirri
liosyrdnoylnO
nieraryreV
ecirdetagirri
liosyrdnoylnO
nieraryreV
ecirdetagirri
desaercnI
telekips
ytilirets
elcinaP
ecnegreme
sliaf
nieraryreV
ecirdetagirri
gnigdoL
desaercnI
foecnedicni
esaesid
aCeFnMuCBiS

A-12
Nitrogen-deficiency symptoms
Stunted, yellowish plants. Older leaves or whole plants are yellowish
green.
Old leaves and sometimes all leaves become light green and chlorotic
at the tip. Leaves die under severe N stress. Except for young leaves,
which are greener, leaves are narrow, short, erect, and lemon-yellowish
green. The entire field may appear yellowish. N deficiency often occurs
at critical growth stages such as tillering and panicle initiation when the
demand for N is large. N deficiency results in reduced tillering, small
leaves, and short plants. Grain number is reduced. The visual symptoms
of N deficiency can be confused with those of S deficiency (Section 2.5),
but S deficiency is less common and tends to first affect younger leaves
or all leaves on the plant.
Photo captions
(a) Leaves are yellowish green in the 0 N omission plot, since fertilizer is
not applied.
(b) Leaves of N-deficient plants are light green, narrow, and smaller.
(c) Tillering is reduced where N is deficient.
(d) Tillering is greater where N fertilizer has been applied.

Nitrogen
(a)
(b)
(d)
(c)

A-14
Phosphorus-deficiency symptoms
Stunted dark green plants with erect leaves and reduced tillering.
P-deficient plants are stunted with greatly reduced tillering. Leaves
are narrow, short, very erect, and “dirty” dark green. Stems are thin
and spindly and plant development is retarded. The number of leaves,
panicles, and grains per panicle is also reduced. Young leaves appear to
be healthy but older leaves turn brown and die. Maturity is delayed (often
by 1 week or more). When P deficiency is severe, plants may not flower
at all. Red and purple colors may develop in leaves if the variety has a
tendency to produce anthocyanin. Leaves appear pale green when P and
N deficiency (Section 2.1) occur simultaneously. Moderate P deficiency
is difficult to recognize in the field. P deficiency is often associated with
other nutrient disorders such as Fe toxicity at low pH (Section 2.13), Zn
deficiency (Section 2.4), Fe deficiency (Section 2.9), and salinity (Section
2.18) in alkaline soils.
Photo captions
(a) Tillering is reduced where P is deficient.
(b) Even under less pronounced P deficiency, stems are thin and spindly
and plant development is retarded.
(c), (d) Plants are stunted, small, and erect compared with normal plants.

(a)
Phosphorus
(c) (d)(b)

A-16
Potassium-deficiency symptoms
Dark green plants have yellowish brown leaf margins or dark brown necrotic
spots first appear on the tips of older leaves.
Under severe K deficiency, leaf tips are yellowish brown. Symptoms
appear first on older leaves, then along the leaf edge, and finally on
the leaf base. Upper leaves are short, droopy, and “dirty” dark green.
Older leaves change from yellow to brown and, if the deficiency is not
corrected, discoloration gradually appears on younger leaves. Leaf tips
and margins may dry up. Yellow stripes may appear along leaf interveins
and lower leaves become droopy. Leaf symptoms of K deficiency
(particularly the appearance of yellowish brown leaf margins) are similar
to those of tungro virus disease. Unlike K deficiency, however, tungro
occurs as patches within a field, affecting single hills rather than the
whole field. When K deficiency is severe, rusty brown spots appear on
the tips of older leaves and later spread over the whole leaf, which then
turns brown and becomes desiccated. Irregular necrotic spots may also
occur on panicles.
Photo captions
(a), (b), (c) Leaf tips and margins become yellowish brown and dry up
under K deficiency.
(d) Plants are more susceptible to pests and diseases, and secondary
infections are common.
(e) Leaf rolling may occur.
(f) Hybrid rice produces more biomass and therefore has a greater K
requirement than inbred rice so that K-deficiency symptoms may occur
earlier in hybrid (left) than inbred rice (right).
(g) Plant growth is restricted in the absence of K.

(a)
(b)
(g)
(e)
(f)
(c) (d)
Potassium

A-18
Zinc-deficiency symptoms
Lower leaves of stunted plants become droopy and dry with dusty brown
spots and streaks 2–4 weeks after transplanting.
Symptoms appear 2–4 weeks after transplanting, with uneven plant
growth and patches of poorly established hills in the field, but the crop
may recover without intervention. Under severe Zn deficiency, tillering
decreases and may stop completely, and the time to crop maturity may
increase. Zn deficiency can also increase spikelet sterility in rice. Midribs,
particularly near the leaf base of younger leaves, become chlorotic.
Leaves lose turgor and turn brown as brown blotches and streaks appear
on lower leaves, enlarge, and coalesce. A white line sometimes appears
along the leaf midrib. Plant growth is stunted and leaf blade size is
reduced. In Japan, Zn deficiency is the cause of the “Akagare Type II”
disorder in rice.
Photo captions
(a) Uneven field with stunted plant growth (foreground).
(b) Tillering is reduced, leaves are droopy and dry up.
(c), (d) Appearance of dusty brown spots and streaks.

(b)
(a)
(c) (d)
Zinc

A-20
Sulfur-deficiency symptoms
Pale green plants, light green-colored young leaves.
In contrast to N deficiency (Section 2.1), where older leaves are affected
first, S deficiency results in yellowing of the whole plant and chlorosis
is more pronounced in young leaves, the tips of which may become
necrotic. There is, however, no necrosis of lower leaves of the type that
occurs in N-deficient plants. Also, compared with N deficiency, leaves are
a paler yellow in S-deficient plants. Because the effect of S deficiency
on yield is more pronounced during vegetative growth, symptoms should
be detected and corrected early. S deficiency is often not properly
diagnosed, as foliar symptoms are sometimes mistaken for N deficiency.
Other symptoms and effects on growth are
4 Reduced plant height and stunted growth.
4 Reduced number of tillers.
4 Plant development and maturity delayed by 1–2 weeks.
Photo captions
(a), (b) The leaf canopy appears pale yellow because of yellowing of the
youngest leaves, and plant height and tillering are reduced.
(c), (d) Chlorosis is more pronounced in young leaves, where the leaf
tips may become necrotic.

(d)
(a)
(c)
(b)
Sulfur

A-22
Silicon-deficiency symptoms
Soft, droopy leaves and culms.
Leaves become soft and droopy; this increases mutual shading, which
reduces photosynthetic activity and results in smaller grain yields.
Occurrence increases of diseases such as blast (caused by Pyricularia
oryzae) or brown spot (caused by Helminthosporium oryzae). Severe
Si deficiency reduces the number of panicles per m2
and the number of
filled spikelets per panicle. Si-deficient plants are particularly susceptible
to lodging.
Photo captions
(a) Decreased resistance to diseases such as Bipolaris oryzae.
(b) Droopy leaves (left) compared with those of normal rice plant (right).
(c) Brown spots on leaves.
(d) On organic soils in Florida, rice plants treated with Si amendments
were more resistant to Bipolaris oryzae and Pyricularia grisea (lighter-
colored fields), compared with untreated fields (darker-colored fields) ©
Elsevier Science (1997).

(a)
(d)
(c)(b)
Silicon

A-24
Magnesium-deficiency symptoms
Orange-yellow interveinal chlorosis on older leaves.
Mg-deficient plants are pale-colored, with interveinal chlorosis first
appearing on older leaves and later on younger leaves as deficiency
becomes more severe. Green coloring appears as a “string of beads”
compared with K deficiency, in which green and yellow stripes run
parallel to the leaf (Section 2.3). In severe cases, chlorosis progresses
to yellowing and finally necrosis in older leaves. Other symptoms and
effects of Mg deficiency are
4 Reduced number of spikelets and reduced 1,000-grain weight.
4 Reduced grain quality (% milled rice, protein, and starch content).
4 Fe toxicity may be more pronounced where Mg is part of multiple
nutrient-deficiency stress involving K, P, Ca, and Mg.
Photo captions
(a) Orange-yellow interveinal chlorosis usually appears first on older
leaves.
(b) Chlorosis may also appear on the flag leaf.
(c) Mg deficiency may also be induced by large applications of K
fertilizer on soils with low Mg status.

Magnesium
(a) (b)
(c)

A-26
Calcium-deficiency symptoms
Chlorotic-necrotic split or rolled tips of younger leaves.
Symptoms are usually visible only under severe Ca deficiency (e.g.,
in pot experiments and soil exhaustion experiments). The tips of the
youngest leaves become white (bleached), rolled, and curled. Necrotic
tissue may develop along the lateral margins of leaves, and old leaves
eventually turn brown and die. Ca deficiency may resemble B deficiency
(Section 2.12), and therefore plant tissue analysis may be required to
distinguish the cause of symptoms. There is little change in the general
appearance of the plant except in cases of acute Ca deficiency. Extreme
deficiency results in stunting and death of the growing point.
Photo captions
(a), (b) Symptoms occur only under severe Ca deficiency, when the tips
of the youngest leaves may become chlorotic-white.

Calcium
(a)
(b)

A-28
Iron-deficiency symptoms
Interveinal yellowing and chlorosis of emerging leaves.
Whole leaves become chlorotic and very pale. The entire plant becomes
chlorotic and dies if Fe deficiency is very severe. Fe deficiency is very
important on dryland soils but often disappears one month after planting.
Fe deficiency results in decreased dry matter production, reduced
chlorophyll concentration in leaves, and reduced activity of enzymes
involved in sugar metabolism.
Photo captions
(a) Fe deficiency is mainly a problem on upland soils.
(b) Interveinal yellowing of emerging leaves.
(c) Plants are stunted and have narrow leaves (left) if Fe deficiency is
severe.

(b) (c)
(a)
Iron

A-30
Manganese-deficiency symptoms
Interveinal chlorosis starting at the tip of younger leaves.
Pale grayish green interveinal chlorosis spreads from the tip of the leaf to
the leaf base. Necrotic brown spots develop later, and the leaf becomes
dark brown. Newly emerging leaves are short, narrow, and light green.
At tillering, deficient plants are shorter, have fewer leaves, weigh less,
and have a smaller root system than plants supplied with sufficient
Mn. Plants are stunted but tillering is not affected. Affected plants are
more susceptible to brown spot (caused by Helminthosporium oryzae).
Mn-deficient rice plants are often deficient in P. In soils where both Mn
deficiency and Fe toxicity occur, Mn-deficient rice plants contain a large
concentration of Fe, and may also show symptoms of bronzing (Section
2.13).
Photo captions
(a) Deficiency is mainly a problem in rice grown in upland and organic
soils with low Mn status.
(b), (c) Leaves are affected by interveinal chlorosis that appears at the
tip of younger leaves.

(a)
(c)(b)
Manganese

A-32
Copper-deficiency symptoms
Chlorotic streaks, bluish green leaves, which become chlorotic near the
tips.
Cu-deficient leaves develop chlorotic streaks on either side of the midrib,
followed by the appearance of dark brown necrotic lesions on leaf
tips. New leaves do not unroll and the leaf tip maintains a needle-like
appearance, while the leaf base appears normal. Tillering decreases.
Pollen viability is reduced under Cu deficiency, resulting in increased
spikelet sterility and many unfilled grains (revealed by analysis of yield
components). Absorption of Cu from the soil solution is inhibited by Zn
and vice versa.
Photo captions
(a) Deficiency mainly occurs in organic soils.
(b) Chlorotic streaks and dark brown necrotic lesions may develop on
the tips of younger leaves.
(c) New leaves may have a needle-like appearance.

(a)
(b) (c)
Copper

Nutrient Toxicities A-35
Diagnostic key for identifying nutrient toxicities in rice
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sevaelrewolno
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stopslacitpille
sevaelno
nostopsnworB
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shtaehs
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gnitnalp
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regnuoynooslA
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smotpmys
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htworgdetnutS
decuderdna
gnirellit
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htworg
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gnirellittub
semitemos
lamron
,htworgdetnutS
gnirellitdecuder
,htworgdetnutS
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slios
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ddd
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ddd
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sliosenilas
dnalpudicA
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nieraryreV
ecirdetagirri
edifluSytinilaSlAeFBnM

A-36
Iron-toxicity symptoms
Tiny brown spots on lower leaves starting from the tip or whole leaves
colored orange-yellow to brown. Black coating on root surfaces.
Symptoms first appear 1–2 weeks (but sometimes 2 months) after
transplanting. First, tiny brown spots appear on lower leaves, starting
from the leaf tips, and spread toward the leaf base. Later, spots combine
on leaf interveins and leaves turn orange-brown and then die. Leaves
are narrow but often remain green. Where Fe toxicity is severe, leaves
appear purple-brown. In some varieties, leaf tips become orange-yellow
and then dry up. Rice plants are more susceptible to Fe toxicity during
early growth stages, when root oxidation capacity is small. Other effects
of Fe toxicity include
4 Stunted growth and greatly reduced tillering.
4 Coarse, sparse, damaged root system with a dark brown to black
coating on the root surface and many dead roots. Freshly uprooted
rice hills often have poor root systems with many black roots
(stained by Fe sulfide). In contrast, healthy roots are uniformly
coated with a smooth covering of orange-brown Fe3+
oxides and
hydroxides.
Photo captions
(a) Tiny brown spots develop on the leaf tip and spread toward the leaf
base.
(b) Leaves turn orange-brown and die.
(c) Symptoms first appear on older leaves.
(a), (d) Under severe Fe toxicity, the whole leaf surface is affected.
(e) Leaf bronzing (left) compared to healthy plant (right).

(c) (d)
(e)
(a)
(b)
Iron

A-38
Sulfide-toxicity symptoms
Interveinal chlorosis of emerging leaves. Coarse, sparse, and blackened
roots.
Leaf symptoms of sulfide toxicity are similar to those of chlorosis caused
by Fe deficiency (Section 2.9). Other diagnostic criteria are similar to
those of Fe toxicity (but Fe toxicity has different visual leaf-deficiency
symptoms, Section 2.13):
4 Coarse, sparse, dark brown to black root system. Freshly uprooted
rice hills often have poorly developed root systems with many black
roots (stains of Fe sulfide). In contrast, healthy roots are covered
with a uniform and smooth orange-brown coating of Fe3+
oxides and
hydroxides.
4 Small concentration of K, Mg, Ca, Mn, and Si content in plant tissue.
Photo caption
Roots of affected plants are coarse, sparse, and blackened.

Sulfide

A-40
Boron-toxicity symptoms
Brownish leaf tips and dark brown elliptical spots on leaves.
B toxicity first appears as chlorosis of the tips and margins of older
leaves. Two to four weeks later, dark brown elliptical spots appear on
these discolored areas, which later turn brown and then dry up. Necrotic
spots are most prominent at panicle initiation. Some varieties exhibit
discoloration only at leaf tips and margins. Vegetative growth does not
decrease markedly.
Photo captions
(a) Brownish leaf tips are a typical characteristic of B toxicity, appearing
first as marginal chlorosis on the tips of older leaves.
(b), (c), (d) Two to four weeks later, brown elliptical spots develop on the
discolored areas.

(a)
(c) (d)(b)
Boron

A-42
Manganese-toxicity symptoms
Yellowish brown spots between leaf veins, extending to the whole interveinal
area.
Brown spots develop on the veins of lower leaf blades and leaf sheaths.
Leaf tips dry out 8 weeks after planting. Mn toxicity can also cause
chlorosis of younger (upper) leaves, with symptoms similar to those of
Fe chlorosis (Section 2.9). Plants are stunted and tillering decreases.
Sterility results in reduced grain yield. Excess Mn uptake reduces Si, P,
and Fe uptake and translocation of P to the panicle.
Photo captions
(a), (b), (c) Interveinal yellowish brown spots develop on lower leaf
blades and leaf sheaths.

(c)(b)
(a)
Manganese

A-44
Aluminum-toxicity symptoms
Orange-yellow interveinal chlorosis on leaves. Poor growth, stunted plants.
Reduced and deformed root growth.
Yellow to white mottling of interveins is followed by leaf tip death and leaf
margin scorch. Necrosis of chlorotic areas occurs if Al toxicity is severe.
Aluminum toxicity reduces shoot and root growth. Varieties differ in their
tolerance of Al toxicity. In susceptible cultivars, roots are stunted and
deformed. Growth is stunted, but tillering may be normal. Retarded root
growth results in reduced nutrient uptake and less drought tolerance.
Photo captions
(a) Aluminum toxicity is mainly a problem in acid upland soils but
varieties differ in their susceptibility.
(b) Yellow to white mottling of interveins is followed by leaf tip death.
(c) Leaf margin scorch.
(d) Indicator plants such as tropical bracken (Dicranopteris linearis),
Straits Rhododhendron (Melastoma malabathricum), and alang-alang
(Imperata cylindrica) provide a proxy indicator of acid soil conditions and
low soil P status.
(e) A pocket pH meter provides a reliable indication of soil pH.

(a)
(b)
(d) (e)
Aluminum
(c)

A-46
Salinity symptoms
White leaf tips and stunted, patchy growth in the field.
Tips of affected leaves are white, and chlorotic patches appear on some
leaves. Salinity results in plant stunting and reduced tillering. Field
growth is very patchy. Symptoms appear in the first leaf, followed by the
second, and then in the growing leaf. Rice is more tolerant of salinity at
germination, but plants may become affected at transplanting, young
seedling, and flowering stages. Salinity or sodicity may be accompanied
by P deficiency (Section 2.2), Zn deficiency (Section 2.4), Fe deficiency
(Section 2.9), or B toxicity (Section 2.15).
Photo captions
(a) Growth is characteristically patchy.
(b) Where saline irrigation water is used, patches of affected plants are
found adjacent to water inlets.
(c), (d) Stunted plants with white leaf tips.

(a)
(d)(b)
(c)
Salinity

New Web site on SSNM
The initial SSNM concept was systematically transformed to
provide farmers and extension workers with simplified approaches
to nutrient management. SSNM has now become an integral
part of crop management strategies promoted by many Asian
countries participating in the Irrigated Rice Research Consortium
(www.irri.org/irrc). The IRRC launced a new Web site on SSNM
(www.irri.org/irrc/ssnm) to provide the rice-growing community
with up-to-date information on the principles and practices of
SSNM for irrigated and favorable rainfed rice systems.
www.irri.org/irrc/ssnm

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2007 International Rice Research Institute,
International Plant Nutrition Institute, and
International Potash Institute.

A Practical Guide to Nutrient Management
Rice
International Rice Research Institute
DAPO Box 7777, Metro Manila, Philippines
Tel +63 2 580 5600
Fax +63 2 580 5699
E-mail irripub@cgiar.org
Web site www.irri.org
www.irri.org/irrc/ssnm
International Plant Nutrition Institute
Southeast Asia Program
A joint mission with the International Potash Institute
126 Watten Estate Road, Singapore 287599
Tel +65 6468 1143
Fax +65 6467 0416
E-mail seasia@ipni.net
Web site www.ipni.net/seasia
ISBN 978-981-05-7949-4
For further information about this guide or other matters relating
to tropical crop production and plant nutrition, contact:

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