subishan scheduling irrigation, water management .pptx

Irrigation management

1. Scheduling irrigation-criteria for scheduling irrigation-crop coefficient.water management of crops under climate change scenario Presentation by M.subishan

2. SCheduling irrigation Irrigation scheduling is the process of determining when to irrigate and how much water to apply. Proper scheduling is essential for efficient use of irrigation water and production inputs such as fertilizer etc. Proper scheduling of irrigation leads to saving in water and energy, higher crop yield, efficient use of inputs and lower production costs. Most farmers follow irrigation practices which are resulting in either under irrigation or over-irrigation of crops. Production per unit of water is, therefore, low. Farmers face two situations: (i) where adequate water is available and their aim is to produce maximum yield per unit of land and unit of water, and (ii) where a limited quantity of water is available and their aim is to produce maximum yield per unit of water.

3. Criteria for scheduling irrigation Several criteria for scheduling irrigations are now available and are being used by investigators and farmers.

4. 1.Soil water regime approach The available soil water held between FC and PWP in the effectiveroot zone depth described in several ways is taken as an index or guide for determining practical irrigation schedules . Alternatively soil moisture tension , is also sometimes used as a guide for time of irrigations A) Feel and appearance of soi l : This is one of the oldest and simple method of determining the soil moisture content. It is done by visual observation and feel of the soil by hand. The accuracy of judgement improves with experience. Though it is a crude method ti can be used satisfactorily for some purpose .

5. Feel and appearance method

6. Guidelines for judging soil moisture by feel and appearance method

7. B. DEPLETION OF AVAILABLE SOIL MOISTURE Permissible depletion level of ASM in the effective crop root zone depth is commonly taken as an index or guide or scheduling irrigation to field crops. In general , for many crops scheduling irrigation’s at 20 -25% DASM is optimum at moisture sensitive stages. While at other stages irrigation are scheduled at 50% DASM.

8. Optimum DASM levels for various crops

9. C. Soil moisture tension Soil moisture tension, a physical property of water in soil, as monitored by tensiometers at a specified depth in the crop root zone used as an index for scheduling irrigations. Tensiometers are installed in pairs, one in the maximum rooting depth and the other below this zone.• Whenever critical soil moisture tension is reached say for example 0.4 or 0.6 or 0.75 bars etc in the upper tensiometer , the irrigation is commenced.• While the lower one ( tensiometer ) is used to terminate the irrigations based on the suction readings in the below soil profile zone .

10. 2. Climatological approach  The water loss expressed in terms of either PET or CPE over short periods of time are taken as an index for scheduling irrigation. Different climatological approaches are PET CPE IW/CPE Ratio

11. A.Potential evapotrnaspiration Penmen (1948) introduced the concept of PET "the amount of water transpired in a unit time by short green crop of uniform height, completely covering the ground and never short of water". He further stated that PET cannot exceed pan evaporation under the same weather conditions PET can be estimated by several techniques viz., lysimetric method, energy balance, aerodynamic approach, combination of energy balance and empirical formulae etc.,

12. B. Cumulative pan evaporation Open pan evaporimeter being simple and used as a guide for scheduling irrigation to crops. For ex. Wheat required 75 to 100 mm CPE at Ludhiana Sugarcane required 75 mm CPE in Maharashtra  Greengram required 180 mm CPE at Ludhiana Sunflower required 60 mm CPE at Bangalore

13. C. IW / CPE RATIO  Prihar et al. (1974) advocated irrigation scheduling on the basis of ratio between the depth of irrigation water (IW) and cumulative evaporation from U.S.W.B. class A pan evaporimeter (CPE). An IW/CPE ratio of 1.0 indicates irrigating the crop with water equal to that lost in evaporation from the evaporim eter .

14. OPTIMUM IW/CPE RATIOS FOR SCHEDULING IRRIGATION IN IMPORTANT CROPS Crop Optimum IW / CPE ratio Groundnut 0.75 to 1.0 Sunflower 0.5 to 1.0 Wheat 1.0 Bengal gram 0.4 Mustard 0.4 Maize 0.75 to 1.0 Sugarcane 0.5 to 1.0

15. 3. Plant indices approach A. VISUAL PLANT SYMPTOMS Plant wilting, drooping, curling and rolling of leaves in maize is used as indicators for scheduling irrigation. Change in foliage colour and leaf angle in beans. Appearance of carotenoid (yellow and orange colour) and anthocyanin pigments; Shortening of internodes in sugarcane and cotton; Retardation of stem elongation in Grapes.

16. B. SOIL-CUM-SAND MINI- PLOT TECHNIQUE Also referred to profile modification technique The principle - to reduce the available WHC of soil profile artificially in the mini-plot by mixing sand with it. An area of 1.0 x 1.0 x 1.0m is selected in the field. About 5% of sand by volume is added to the dug up soil and mixed well. The pit is then filled back with the mixture Crop is sown normally and is allowed to grow as usual with the rest of the field. • plants growing on the sand mixed plot show wilting symptoms earlier than in the rest of the field.

17. C. PLANT POPULATION Increase in plant population by 1.5 to 2.0 times that of optimum in some representative spots of (1 m x 1m area in the cropped field more plants per unit area, the available water within that zone is depleted rapidly as compared to other area wherein optimum number of plants is maintained. This result in drooping or wilting of plants earlier, which can be taken as an indication of water deficits and accordingly irrigations are scheduled to crops.

18. D. RATE OF GROWTH Growth of a plant is dependent on turgor, which in turn is dependent on a favourable soil water balance. So fluctuations in the water balance are reflected by parallel fluctuations in the growth rate of expanding organs. Stem elongation is markedly reduced when the available soil moisture level at critical, but accelerates again after irrigation.

19. E. RELATIVE WATER CONTENT It is the actual water content of the leaf or plant when sampled is expressed as relative water content (RWC) It depends on the lag between evaporative demand of the atmosphere and the rate of water absorption by the roots. The critical RWC level (below which reduction in growth occurs) for cotton and sesame was 72% and 75% respectively. Whenever the plant exhibits these values, irrigations can be scheduled. Tedious and time consuming.

20. F. PLANT WATER POTENTIAL Plant / leaf water potential can be measured either by a pressure bomb or pressure chamber apparatus in situ or by the dye method in the laboratory. The critical plant water potential values for cotton below which yield reductions are expected were 1.2 to 1.25 MPa throughout the crop life. While for sunflower they were 1.0,1.2 and 1.4 MPa at vegetative, pollination and seed formation, respectively.

21. LEAF WATER POTENTIAL Leaf water potential indicates the plants need for water. Leaf water potential is measured by removing a leaf and placing it in a pressure chamber. The pressure in the chamber is slowly increased until fluid is forced from the leaf. The pressure used is a measure of the leaf's moisture potential. Lower potentials indicate a greater need for water. The leaf age, leaf exposure to solar radiation and time of day when leaf is sampled all significantly influence the results. This method is not extensively used since considerable time, care and training are required to obtain reliable results.

22. G. CANOPY TEMPERATURE Plant or canopy temperature adequately reflects the internal water balance of the plant, and can be used as a potential indicator for scheduling irrigation. Measured by several instruments viz., Porometer , Infrared thermometer etc. For maize - canopy temperature rises to more than 0.7 °C over ambient temperature during 13.30 to 14.00 hrs irrigations need to be scheduled. However, tomato showed no sensitivity to water stress with respect to temperature variations.

23. H. INDICATOR PLANTS Some workers have suggested the use of indicator plants as a guide for scheduling irrigations. In wheat, scheduling irrigations on the basis of wilting symptoms in maize and sunflower gave the highest grain yields.

24. I. CRITICAL GROWTH STAGES  The most critical stage of crop growth is the one at which a high degree of water stress would cause maximum loss in yield. Scheduling of irrigations on the basis of critical growth stages is simple and easy for the farmers. However, it does not take into account of the available soil water in the crop root zone depth. The criterion may not hold well in long duration crops like sugarcane, cotton Crops requiring frequent irrigation's viz., potato or Standing/nearly standing water (rice) and Where there is interference by rainfall of different amounts.

25. Crop Critical growth period for water supply Rice Primordial development, Heading & Flowering Sorghum Booting, Blooming, Milky & Dough stages Ragi Primordial initiation & Flowering Maize Tasseling, Silking & Pollination Bajra Heading & Flowering Wheat Crown root initiation, Shooting & Earing Groundnut Flowering, Peg penetration & Pod development Sesame Flowering to Maturity Sunflower Star formation, Flowering & Seed development Safflower Rosette, flowering and Seed development Soybean Flowering & Seed formation Cotton Flowering & Boll development Sugarcane Formative & Stem elongation Tobacco Rapid growth & Topping stage

26. CROP COEFFICIENTS (K C ) Refers to the ratio between crop ET and reference crop ET. Crop Coefficient curve is constructed by dividing crop growing period into four as follows: Initial period - planting to 10% ground cover Crop development - 10% ground cover to effective cover i.e., flowering Mid-season - Effective cover to start of maturity i.e., senescence of leaves Late season - Start of maturity to harvest.

27. IN ANNUAL CROPS Kc is low at seedling, emergence and establishment stage, increases with increase in ground cover and attains maximum at mid-season stage and thereafter decreases towards ripening and maturity stage For most crops the value for total growing period is between 0.85 to 0.90 with the exception of a higher value for rice and banana. In general Kc is higher in hot, windy and dry climates than in cool, calm and humid climates. The Kc values vary among crops due to differences in reflectivity, crop height and roughness, degree of ground cover and canopy resistance to transpiration.

28. CROP COEFFICIENT CURVE

29. WATER MANAGEMENT OF CROPS UNDER CLIMATE CHANGE SCENARIO Efficient Irrigation Techniques: Adopting drip irrigation, sprinkler systems, or moisture sensors to optimize water use. Crop Selection: Choosing drought-resistant or tolerant crop varieties can mitigate water stress. Soil Health: Improving soil structure and organic matter content enhances water retention and reduces runoff. Rainwater Harvesting: Collecting and storing rainwater for irrigation during dry periods. Cover Crops: Planting cover crops helps retain soil moisture and prevent erosion

30. CONTD ., Agroforestry: Introducing trees or shrubs into crop systems can help regulate soil moisture and microclimate. Water Recycling: Reusing treated wastewater for irrigation to supplement freshwater sources. Adaptive Management: Regularly monitoring weather patterns and adjusting irrigation schedules accordingly. Policy Support: Implementing policies that promote sustainable water use and support farmers in adopting water-saving technologies.