Soil testing

Soil Testing

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Introduction:

We all know that health of soil is equally
important as health of any person. It is
more applicable when it comes to ‘farming’.
But, it is observed that now a day, ‘health
of soil’ doesn’t get enough attention. People
care more about only ‘cash crops and
increasing quantity of the crop’. As a result
of this, soil becomes unproductive.
Awareness about ‘soil health’ should be
increased to avoid this.

Why do we need ‘Soil Testing’?
Soil is an important matter for cultivation of any type of crop.
Soil supplies many necessary nutrients required for healthy
growth of a crop. The yield is largely dependent on the soil in
which the crop grows. So, before cultivation, it is very important
to check the soil for its nutrients. By checking the soil you will
know whether the soil is having enough amount of nutrients or not.
If any nutrient is less or more than the required
amount, necessary measures can be taken.

In short following are the benefits of ‘soil testing’:
•Soil testing encourages plant growth by providing the best
fertilizer recommendations.
•It diagnoses whether there is too little or too much of a
nutrient.
•‘Soil testing’ promotes environmental quality.
•It also saves money that might otherwise be spent on unneeded
fertilizer.

When and How to take a sample of a soil?
Soil sample must be taken at the right time and in the
right way as described here:
Before planting anything in the field and after you
take out the crop
Before application of any organic or chemical
fertilizers
Three months after application of any organic or
chemical fertilizers.

Do not take soil samples from the
following areas:
Where cattle graze
Under a tree
Garbage area

Only 0.5 kg soil is required for soil testing.

Following is the correct procedure to collect soil for ‘soil
sample’.

Procedure
1. For ‘soil testing’, soil is taken from 15 different places.
2. Dig a ‘V’ shape pit in the ground which is 15 cm deep. Take
soil sample (2 to 3 cm thick) from one side of it.
3. Follow the same procedure to take samples from 15
different places.
4. Clean the samples by removing any garbage if present in the
soil.
5. Mix all the samples very well (Make 4 equal parts of the
mixed sample. Then mix two diagonally opposite parts with
each other. Repeat the procedure for 4/5 times)
6. Take 0.5 kg of the sample for ‘soil testing’.

Dig the pits as per the following figure. Yellow circles show
location for the pit.

Dig each pit as shown in the figure. Take soil from the
area shown in ‘brown’.

Floor surface

Plants need 16 essential nutrients for healthy growth
and development.

Necessary nutrients for crop growth:
Main nutrients:
Nitrogen (N), Phosphorus (P), Potassium(K)
Secondary nutrients:
Calcium (Ca), Magnesium (Mg), Sulphur (S)
Micro nutrients:
Iron (I), boron (B), zinc (Zn), copper (Cu),
molybdenum (Mo), chlorine (Cl), maganese(Mn)
Nutrients from air:
Carbon (C), hydrogen (H)
Nutrients from water:
Oxygen (O)
Apart from above nutrients, there are some other parameters
which also affect plant growth. These parameters are: Soil pH, Soil
EC (Electrical Conductivity) and Soil OC (Organic Carbon). To judge
the health of soil, these parameters should be checked.

Signs shown on plants because of nutritional
deficiency
Nitrogen – Tree doesn’t get average
height. Leaves become yellow.

Phosphorus – Growth of a plant stops

Potassium – Leaves become reddish
yellow on the edges while inner part
of the leaves remain green.

Calcium – Tender leaves dry and plant dies.

Magnesium – Leaves start drying from the tip.

Sulphur – Brownish spots on leaves.

Iron – Main veins of a leaf become green.

Manganese – Younger leaves show chlorotic spots between
the veins.

Copper – Leaves become yellow and stop growing and
then fall off.

Boron – Young leaves become light in colour from
petiole and start folding.

Molybdenum – Yellow/orange spots all over on matured
leaves.

pH of soil

Apart from soil nutrients one more factor affect the
yield. That factor is ‘pH’.

The soil pH is a measure of the acidity or basicity in
soils. It is measured in pH units. The pH scale goes from
0 to 14 with pH 7 as the neutral point.

Hydrogen ions present in the soil decide pH value of the
soil. When +ve ions get washed off through water, soil
becomes acidic. Similarly, when amount of
Calcium, Sodium in soil increases, soils become alkaline.
Simply we can say that low pH means sour and high pH
means salty soil.

pH testing is important because
nutrient mobility ( transfer of
nutrients ) from soil to plant
through roots depends on pH of
the soil.

Diagrams shows availability of
nutrients according to its pH -

**We are using a readymade kit from ‘Prerana Lab’ for all the
tests. So, the procedures are given assuming that you have
‘Prerana Lab kit’ with you to carry out the tests. Contact
Details of Prerana Lab are given on the last slide.**

Checking pH of soil

1. Take 5 ml of pH-1 solution in the test bottle no. 1.
2. By using a funnel, add two teaspoon (approx. 2 gm) soil
sample in the test bottle no. 1
3. Put the cap on the bottle and gently shake it for a minute.
4. Then keep the bottle still for 10 minutes. Now the soil will
settle down and there will be a layer of clear liquid on the
top of it.
5. Place the test bottle in the pH colour comparator and
compare the colour of the liquid in the test bottle with the
colour on the comparator.
6. Note down the pH accordingly.

Soil type according to its pH value:

pH value Soil type

Below 4.5 Extremely acidic
4.5-5.0 Highly acidic
5.0-6.0 Medium acidic
6.0-6.5 Slightly acidic
7.0 Neutral
7.0-7.5 Slightly alkaline
7.5-8.0 Medium alkaline
8.5-9.0 Highly alkaline
Above 9.0 Extremely alkaline

How to increase pH of the soil?
According to the existing pH of the soil, use Lime powder (Calcium
carbonate or dolomite limestone) to increase the pH. 0.5-2.50 tons
of Lime powder per hector of farm.

Use organic and grass fertilizers.

How to reduce pH of the soil?

If pH of soil is more, that means –ve ion
deposited, soil becomes salty (alkaline). For small
correction (if pH is slightly high @ 8 to 8.5) leaching
of these ions will be useful. For leaching these
deposited ions preparing trenches toward slop of land
/ fixing purported pipes (earthen / PVC) below 3 ft in
soil can be done.
Similarly, green manuring with crops like sunhemp
(dencha) , Jute (Tag) etc are also helpful.
For highly alkaline soils ( pH more than 8.5), gypsum
(Sulphar) can be used. (Quantity of Sulphar is
decided on the basic of soil type and pH of soil).

How to reduce the salts in the soil?

Scratch out all the salts which are there on the
surface of the soil.

Make small compartments (of a height of 1 feet)
of the field and fill it with water.
Keep the water there for some time and let it
go at once through an outlet. This way all salts
will be washed off.
Make sure that water is draining out properly.
Use plenty of organic fertilizers.

Checking Nitrogen content in the soil
We are using a readymade kit from ‘Prerana Lab’ for this test.

1. Take 6 ml AN-1 solution in the test bottle no. 1.
2. By using a funnel, add one teaspoon (approx. 1 gm) soil sample in the
test bottle no. 1
4. Then keep the bottle still for 5 minutes. Now the soil will settle
down and there will be a layer of clear liquid on the top of it.
5. Now, in an another test bottle (test bottle no. 2), take 2 ml clear
liquid from test bottle no. 1 with the help of a dropper. Make sure
that there won’t be any traces of soil from test bottle no. 1 in the
dropper.
6. Add 4 drops of AN-2 solution in test bottle no. 2.
7. Put the cap on the bottle and shake it gently.
8. Keep the bottle still for 5 minutes.
9. Now shake the bottle and compare the colour of the solution in the
bottle (test bottle no. 2) with the colour screen given in the kit.
10. Note down the Nitrogen content in the soil accordingly.

Checking Phosphorus content in the soil

1. Take 6 ml of EP-1 solution in the test bottle no. 1.
2. By using a funnel, add one teaspoon (approx. 1 gm) soil sample in the test
bottle no. 1.
4. Then keep the bottle still for 5 minutes. Now the soil will settle down and
there will be a layer of clear liquid on the top of it.
5. Now, in an another test bottle (test bottle no. 2), take 3 ml clear liquid
from test bottle no. 1 with the help of a dropper. Make sure that there
won’t be any traces of soil from test bottle no. 1 in the dropper.
6. Add 6 drops of AP-2 solution in test bottle no. 2.
7. Put the cap on the bottle and shake it gently.
8. Now add 2 drops of AP-3 solution in test bottle no. 2.
9. Put the cap on the bottle and shake it well.
10. Now, the solution in test bottle no. 2 will look blue in colour.
11. Compare this colour with the colour on ‘Phosphorus colour chart’ and
accordingly note down the available phosphorus content in the soil.

Checking Potassium content in the soil:
1. Take 6 ml of AK-1 solution in test bottle no. 1.
2. By using a funnel, add two teaspoon (approx. 2 gm) soil sample in the test
bottle no. 1.
4. Then keep the bottle still for 5 minutes. Now the soil will settle down
and there will be a layer of clear liquid on the top of it.
5. Now, in an another test bottle (test bottle no. 2), take 2 ml clear liquid
from test bottle no. 1 with the help of a dropper. Make sure that there
won’t be any traces of soil from test bottle no. 1 in the dropper.
6. Add one tablet of AK-2 in the test bottle no. 2.
7. Let the tablet dissolve in the solution. (Do not put the cap on the bottle.
It will take 5 to 6 minutes for the tablet to dissolve completely)
8. By now, colour of the solution in the test bottle no. 2 will change to light
purple.
9. Now, take 1 ml of AK-4 solution in the red coloured syringes (available in
the kit).
10. Add this solution (AK-4) in the test bottle no. 2 drop by drop till the
colour of the solution in the bottle becomes blue.
Continued…

Continued from last slide…
11. Keep a count of no. of drops of AK-4 solution added in the test
bottle no. 2 to change the colour of the solution.
12. Refer the following chart to know the potassium content in the soil.

Colour
change

Drop count of AK-4 Available Potassium Potassium content
(kg/hector) in the soil
More than 22 drops Less than 100 Very less
21 to 22 drops 100-150 Less
19 to 20 drops 150-200 Medium
17 to 18 drops 200-250 Average
15 to 16 drops 250-300 High
Less than 15 drops More than 300 Very high

Organic Carbohydrates (OC)

OC is a measure of organic matter available in the soil.
It shouldn’t be less than 2% and shouldn’t be more than
30%. Bacteria grow properly if OC is in a proper limit.
Carbon-Nitrogen (C:N) ratio also remains good in proper
OC limit.

*C:N ratio - C:N ratio means ratio between Carbon present in the
soil to the ration of nitrogen present in the soil. Say for example if
C:N ration of soil is 10:1 that means there is 10 part of carbon to
each part of nitrogen in the soil. All living organisms require to
produce energy for their survival and for that they need carbon as
their main source of energy. But if carbon (OC) contain in soil is
very less then micro-organisms will try to use nitrogen for their
energy needs. This will lead to reduction in nitrogen content of
soil, which is very important for plant growth.

Checking OC content available in the soil


1. Take 100 mg sample soil in test bottle no. 1.
2. Take 0.5 ml of OC-1 solution with the help of Green syringes and
add that to test bottle no. 1.
3. Then add 80 drops of OC-2 solution in the same test bottle. (Do
this very carefully as this contain concentrated acid).
4. Put the cap on the bottle and shake the bottle gently.
5. Take 5 ml of OC-3 solution and add it in the test bottle no. 1.
Now keep the bottle still for 5 min. so that soil will set down and
you will get a clear layer of liquid on the top. This liquid will have
a colour.
6. Place this bottle in ‘organic carbon colour comparator’ to compare
the colour of the liquid in the bottle with matching colour on the
comparator.
7. Note down the percentage of organic carbon available in the soil
accordingly.

Suggesting fertilizers according to the ‘soil testing’ results

Main objective of soil testing is to know the content or amount of
nutrients (for eg. Nitrogen, Phosphorus, Potassium, pH, Organic carbon
etc.) available in the soil. Balanced amount of all these nutrients are very
important for healthy growth of any crop.

Fertilizers are suggested depending upon the amount of nutrients
available in the soil as well as requirement of the same for the crop. Soil
nutrients are generally measured as ‘low, medium and high’.

•If available soil nutrients are very low, increase the dose of fertilizer by
50%.
•If available soil nutrients are low, increase the dose of fertilizer by 25%.
•If available soil nutrients are medium or slightly more than medium, no
need to change the fertilizer dose.
•If available soil nutrients are very high, reduce the dose of fertilizer by
50%.
•If available soil nutrients are high, reduce the dose of fertilizer by 25%.

Contact Details of Prerana Lab:

Prerna Laboratory,
Prerna house,
Plot No- 8, Near Chatrapati Bank,
Vishal Nager (Jagtap dairy),
Aundh-Wakad road,
Pune -411028.
Phone – 27274958 / 9371015199.

References:

www.vasat.icrisat.org
www.faculty.rpcs.org
http://www.terragis.bees.unsw.edu.au/terraGIS_soil/sp_soil_re
action_ph.html

Soil testing

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