Agl111 Lecture-2
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This document discusses soil-plant and plant-water relations, including rooting characteristics of different plant types, factors influencing root development, types of water movement in soil, and water absorption by plants. It also covers crop water requirements, water use efficiency, scheduling irrigation using different methods, and quality of irrigation water including criteria used to determine quality and management practices for using poor quality water.
Agl111 Lecture-2
- 1. Career Point Cares Fundamentals of Agronomy (AGL111) Mr. Rohitashv Nagar Assistant Professor & HOD Department of Agronomy School of Agricultural Sciences Career Point University, Kota (Raj.)
- 2. Career Point Cares Lecture-2 Soil – Plant and Plant – Water Relations
- 3. Career Point Cares Soil – Plant and Plant – Water Relations • To design a successful irrigation system, it is essential to know the plant rooting characteristics, effective root zone depth, moisture extraction pattern and moisture sensitive periods of crops. • Rooting characteristic of plants: The purpose of irrigation is to provide adequate soil moisture in the immediate vicinity of the plant roots. All plants do not have the similar rooting pattern i.e., root penetration and proliferation. Some plants have relatively shallow root system (for example annual crops), while others develop several meters under favorable conditions (for example tree crops).
- 4. Career Point Cares Soil properties influencing root development 1. Hard pan: Root penetration is seriously affected by presence of a hard pan or compacted layer in the soil profile. Thus roots cannot penetrate a hard layer except through cracks. 2. Soil moisture: Since roots cannot grow in soil that is depleted in moisture down to and below the permanent wilting point, a layer of dry soil below the surface in the profile can restrict root penetration.
- 5. Career Point Cares 3. Water table: A high water table limits root growth, and a rising water table may kill roots that have previously grown below the new water level. 4. Toxic substances: Presence of toxic substances in the sub-soil also limits root growth and development. Saline layers or patches in the soil profile therefore inhibit or prevent root penetration and proliferation.
- 6. Career Point Cares Types of water movement • Generally three types of water movement within the soil are recognized –saturated flow, unsaturated flow and water vapour flow. 1. Saturated water movement: The condition of the soil when all the macro and micro pores are filled with water the soil is said to be at saturation, and any water flow under this soil condition is referred to as saturated flow.
- 7. Career Point Cares 2. Unsaturated water movement: The soil is said to be under unsaturated condition when the soil macro pores are mostly filled with air and the micro pores (capillary pores) with water and some air, and any water movement or flow taking place under this soil condition is referred to as unsaturated flow.
- 9. Career Point Cares Water absorption by plants Mechanism of Absorption of Water: In higher plants water is absorbed through root hairs which are in contact with soil water and form a root hair zone a little behind the root tips. Mechanism of water absorption is of two types: 1. Active Absorption of Water: In this process the root cells play active role in the absorption of water and metabolic energy released through respiration is consumed.
- 10. Career Point Cares 2. Passive Absorption of Water: It is mainly due to transpiration, the root cells do not play active role and remain passive.
- 12. Career Point Cares Crop water requirement Water requirement or irrigation requirement : Water requirement of a crop is the quantity of water regardless of source, needed for normal crop growth and yield in a period of time at a place and may be supplied by precipitation or by irrigation or by both. Water is needed mainly to meet the demands of evaporation (E), transpiration (T) and metabolic needs of the plants, all together known as consumptive use (CU). WR = CU + application losses + water needed for special operations.
- 13. Career Point Cares Water requirement (mm) of important crops Crop Water Requirement (mm) Crop Water Requirement (mm) Rice 900-2500 Soybean 450-700 Wheat 350-600 Potato 450-500 Barley 300-350 Peas 150-200 Maize 500-550 Pigeonpea 250-300 Sorghum 500-600 Chickpea 250-300 Pearl Millet 500-550 Beans 300-500 Sugarcane 1400-2500 Tomato 600-800 Cotton 500-750 Onion 700-800 Tobacco 600-650 Cabbage 380-500 Jute 500-600 Banana 1200-2200 Groundnut 600-700 Citrus 900-1200
- 14. Career Point Cares Water use efficiency It is the ratio of the quantity of dry matter produced to the total depth of water consumed during the entire crop growth season and is expressed as kg per cm. 1. Crop water-use efficiency: It is the ratio of crop yield (Y) to the amount of water depleted by the crop in the process of evapotranspiration. Crop water-use efficiency: Y/ET 2. Field water-use efficiency: it is the ratio of crop yield (Y) to the amount of water used in the field (WR). Field water-use efficiency: Y/WR
- 15. Career Point Cares Scheduling Irrigation : Irrigation schedule must indicate when irrigation water is to be applied and the quantity of water to be applied. Advantages of Irrigation Scheduling : • It enables the farmer to schedule water rotation among the various fields to minimize crop water stress and maximize yields. • It reduces the farmer’s cost of water and labour • It lowers fertilizer costs by holding surface runoff • It increases net returns by increasing crop yields and crop quality.
- 16. Career Point Cares Scheduling Irrigation Methods 1. Soil water regime approach : In this approach the available soil water held between field capacity and permanent wilting point in the effective crop root zone. Alternatively soil moisture tension, the force with which the water is held around the soil particles is also sometimes used as a guide for timing irrigations. 2. Climatological Approach : The potential rate of water loss from a crop is primarily a function of evaporative demand of the atmosphere .In this method the water loss expressed in terms of either potential evapotranspiration (PET).
- 17. Career Point Cares 3. Plant Indices Approach : • Visual plant symptoms : • In this method the visual signs of plants are used as an index for scheduling irritations. • For instance, plant wilting, drooping, curling and rolling of leaves in maize is used as indicators for scheduling irrigation. • Change in foliage colour and leaf angle is used to time irrigations in beans. • shortening of internodes in sugarcane and cotton; retardation of stem elongation in grapes.
- 18. Career Point Cares Lecture-3 Quality of Irrigation Water
- 19. Career Point Cares Introduction • All irrigation waters are not pure and may contain some soluble salts. In arid and semi-arid regions successful crop production without supplemental irrigation is not possible. Irrigation water contains 10 – 100 times more salt than rain water.
- 20. Career Point Cares Salinity buildup process in irrigated soils
- 21. Career Point Cares Criteria to determine the quality of irrigation water • The criteria for judging the quality of irrigation water are: Total salt concentration as measured by electrical conductivity, relative proportion of sodium to other cations as expressed by sodium adsorption ratio, bicarbonate content, boron concentration and soluble sodium percentage.
- 22. Career Point Cares 1. Total soluble salts: • Salinity of water refers to concentration of total soluble salts in it. It is the most important single criterion of irrigation water quality. The harmful effects increase with increase in total salt concentration. The concentration of soluble salts in water is indirectly measured by its electrical conductivity (ECw). The quality of saline waters has been divided into five classes as per USDA classification. • Adverse effects of saline water include salt accumulation, increase in osmotic potential, decreased water availability to plants, poor germination, stunted growth with smaller, thicker and dark green leaves, leaf necrosis & leaf drop, root death, wilting of plants, nutrient deficiency symptoms and poor crop yields.
- 23. Career Point Cares Salinity class Electrical conductivity Micro mhos/cm Milli mhos/cm C1 – Low < 250 < 0.25 C2 – Medium 250 – 750 0.25 – 0.75 C3 – Medium to high 750 – 2250 0.75 – 2.25 C4 – High 2250 – 5000 2.25 – 5.00 C5 – Very high > 5000 > 5.00 Salinity classes of irrigation water
- 24. Career Point Cares 2. Sodium Adsorption Ratio (SAR): SAR of water indicates the relative proportion of sodium to other cations. It indicates sodium or alkali hazard. The ion concentration is expressed as meq per litre. Increase in SAR of water increases the exchangeable sodium percentage (ESP) of soil. There is a linear relationship between SAR and ESP of the soil.
- 25. Career Point Cares Sodium class SAR value S1 – Low < 10 S2 – Moderate 10 – 18 S3 – High 18 – 26 S4 – Very high > 26 Harmful effects of sodic water include destruction of soil structure, crust formation, poor seedling emergence, reduction in availability of N, Zn and Fe due to increased soil pH, Na toxicity and toxicity of B & Mo due to their excessive solubility. Sodicity classes of water
- 26. Career Point Cares 3. Boron content: Though boron is an essential micronutrient for plant growth, its presence in excess in irrigation water affects metabolic activities of the plant. For normal crop growth the safe limits of boron content. Boron (ppm) Quality rating < 3 Normal 3 – 4 Low 4 – 5 Medium 5 – 10 High More than 10 Very high Permissible limits of boron content in irrigation for crops
- 27. Career Point Cares Management practices for using poor quality water a) Application of gypsum: Chemical amendments such as gypsum, when added to water will increase the calcium concentration in the water, thus reducing the sodium to calcium ratio and the SAR, thus improving the infiltration rate. Gypsum requirement is calculated based on relative concentration of Na, Mg & Ca ions in irrigation water and the solubility of gypsum. To add 1 meq /L of calcium, 860 kg of gypsum of 100% purity per ha m of water is necessary.
- 28. Career Point Cares b) Alternate irrigation strategy: Some crops are susceptible to salinity at germination & establishment stage, but tolerant at later stage. If susceptible stages are ensured with good quality water, subsequent tolerant stages can be irrigated with poor quality saline water. c) Fertilizer application: Fertilizers, manures, and soil amendments include many soluble salts in high concentrations. If placed too close to the germinating seedling or to the growing plant, the fertilizer may cause or aggravate a salinity or toxicity problem. Care, therefore, should be taken in placement as well as timing of fertilization. Application of fertilizers in small doses and frequently improve uptake and reduce damage to the crop plants. In addition, the lower the salt index of fertilizer, the less danger there is of salt burn and damage to seedlings or young plants.
- 29. Career Point Cares d) Methods of irrigation: The method of irrigation directly affects both the efficiency of water use and the way salts accumulate. Poor quality irrigation water is not suitable for use in sprinkler method of irrigation. Crops sprinkled with waters having excess quantities of specific ions such as Na and Cl cause leaf burn. High frequency irrigation in small amounts as in drip irrigation improves water availability and uptake due to micro-leaching effect in the wetted zone.
- 30. Career Point Cares e) Crop tolerance: The crops differ in their tolerance to poor quality waters. Growing tolerant crops when poor quality water is used for irrigation helps to obtain reasonable crops yields. Relative salt tolerance of crops. f) Method of sowing: Salinity reduces or slows germination and it is often difficult to obtain a satisfactory stand. Suitable planting practices, bed shapes, and irrigation management can greatly enhance salt control during the critical germination period. Seeds have to be placed in the area where salt concentration is less. Salt accumulation is less on the slope of the ridge and bottom of the ridge. Therefore, placing the seed on the slope of the ridge, several cm below the crown, is recommended for successful crop establishment.
- 31. Career Point Cares Tolerant Field crops: Cotton, Safflower, Sugar beet & Barley Fruit crops: Date palm & Guava Vegetables: Turnip & Spinach Semi tolerant Field crops: Sorghum, Maize, Sunflower, Bajra, Mustard Rice & Wheat Fruit crops: Grape & Mango Vegetables: Tomato, Cabbage, Cauliflower, Cucumber, Carrot & Potato Sensitive Field crops: Chick pea, Linseed, Beans Greengram & Blackgram Fruit crops: Apple, Orange, Almond, Strawberry, Lemon Vegetables: Radish, Peas & Lady’s finger
- 32. Career Point Cares g) Drainage: Provide adequate internal drainage. Meet the necessary leaching requirement depending on crop and EC of water. This is necessary to avoid build of salt in the soil solution to levels that will limit crop yields. Leaching requirement can be calculated from water test results and tolerance levels of specific crops. h) Mulching: Mulching with locally available plant material help in reducing salt problems by reducing evaporation and by increasing infiltration.