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PRINCIPLES OF IRRIGATION

PRINCIPLES OF IRRIGATION. Irrigation is the supplying of water to crops by the growers. Irrigation is needed when the water requirement of a crop exceeds the natural supply. Natural supply of water to crops (rainfall, soil and water storage). Why water is essential for crops. Water is

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PRINCIPLES OF IRRIGATION

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  1. PRINCIPLES OF IRRIGATION • Irrigation is the supplying of water to crops by the growers. Irrigation is needed when the water requirement of a crop exceeds the natural supply. • Natural supply of water to crops (rainfall, soil and water storage)

  2. Why water is essential for crops Water is 1. essential for proper internal functioning in plant cells. 2. essential for absorption of plant nutrient from the soil 3. required to facilitate field operations. • Land preparation, Weed control 4. required for soil applied agrochemicals to be effective.

  3. Determination of Crop Water Requirement • Total crop water required by a crop for its whole duration to grow and produce yield. • The water requirement is equal to the sum of Transpiration from the plant Evapotranspiration (ET) Evaporation from the soil

  4. Factors that determine the ET

  5. Crop water requirement = Actual Evapotranspiration Actual Evapotranspiration = kc x Potential Evapotranspiration

  6. Potential Evapo-transpiration (ETp) • ETp is define as the maximum possible ET rate when there is (1) Unlimited supply of water to a crop (2) Canopy covers the ground surface completely

  7. Estimation of ETp • For practical purpose ETp is determine by measuring the pan evaporation (PE) • PE is the amount of water evaporated within a day from an evaporation pan. An evaporation pan is just a container of water made to standard specification.

  8. Cont……. • PE is usually expressed as a depth of water evaporated in mm per day.

  9. Cont….. ETp = kp x PE • Where kp is termed the pan coefficient. The value of kp is specific to each pan. • It is already determine and given to the user. Therefore ETp can be estimated by measuring PE.

  10. Cont…… • After we have define the maximum possible ET rate (i.e. ETp) the next step is to define the actual ET rate (ETa) ETa =< ETp • The next step is to define a relationship between ETa and Etp. This can be given as follows; ETa = ETp x kc • Where kc is called crop coefficient. The value of kc can vary between o (when ETa is zero) and 1 (when ETa=ETp)

  11. Cont…. The value of kc of a crop determined by • Crop Species Different crop species can have different kc values because of inherent differences in their canopy characteristics.

  12. 2. Growth stage if the crop • Kc varies at different growth stages of a crop largely because of the variation in its ground cover as measured by its Leaf Area Index (LAI).

  13. Kc maturity Initial growth stage DAS

  14. Determination of Irrigation requirements • Irrigation requirement refers to the amount of water that should be provided to the crop through irrigation. • Part of the crop water requirement is fulfilled by the natural supply of water which include,

  15. 1. Soil water storage (S) • This refers to the amount of available water stored in the soil profile at the beginning of the season. Available water refers to the part of soil water that could be absorbed by crop root systems. 2. Rainfall (RF) • This refers to any rainfall which occurs after crop establishment.

  16. Cont….. • If the total natural supplies water (S + RF) exceeds the crop water requirement (ETa) there is no need of irrigation. • However if (S+ RF) < ETa then irrigation requirement can be calculated as: Irrigation Requirement = ETa – (S + RF) + L • Where L refers to water loss during application (i.e. irrigation), because no irrigation method is completely efficient.

  17. Cont.. • Therefore we can summarize the factors that have to be considered in estimating the irrigation requirement of a crop as follows. (a) Crop coefficient (kc) and its variation with the age of the crop (b) Potential ET and its controlling factors Climatic factors Crop factors (c) Rainfall Amount Distribution of rainfall over the time

  18. Cont….. (d) Available water in the soil It depends on soil characteristics which will determine the water holding capacity of the soil. (e) Wastage of water during application It depends on the method of water application.

  19. IRRIGATION METHODS Flood irrigation Surface irrigation Basin irrigation Furrow irrigation Irrigation methods Trench irrigation Sub surface irrigation Perforated pipes Sprinkler irrigation Improved systems Drip irrigation

  20. Flood irrigation Water is allowed from the channel into the entire field. Advantages- Labor requirement is minimum. Disadvantages Uneven distribution of water Low water application efficiency

  21. Basin irrigation • Field is divided into small plots surrounded by bunds on all four sides. • Water from the head channel is supplied to the field channel one after the other. • Each field channel supplies water to two rows of basins and water is applied to one basin after another.

  22. Cont…… Advantages • Adopt well to flat topography • Allow high utilization of water • Easy to manage Disadvantages • More labour is required for field layout and irrigation • More land is wasted under channels and bunds • Difficult to remove excess water rapidly during rainfall.

  23. Furrow irrigation • Small furrows are formed in the field and water is diverted into furrows. • Water in the furrow moves downward and lateral directions to wet the soil.

  24. Cont….. Advantages • No partial submergence or temporary flooding • Provide good field drainage • Wets only half to one third of the land surface. Disadvantages • Erosion hazards in the steep slopes. • Concentration of the salt in the ridges • Poor lateral water spread in sand soils

  25. Sprinkler irrigation • In this method water applied as a spray or as rain drops over the crop. • Advantages • Uniform application efficiency • High application efficiency • Suitable for sandy soils • Suitable method of irrigation for rolling and step slope topography.

  26. Cont….. Disadvantages • Does not work well under high wind velocity • Areas with hot dry winds, considerable amount of water is lost as evaporation • Power requirements are high. • High initial cost.

  27. Drip irrigation • This system involves the slow application of water drop by drop to the root zone of a crop. Pipelines are consist of emitters located at selected points along water delivery line. • Advantages • water is used very economically • Fertilizer and other agrochemicals can be applied with water. • Good for water scarcity areas

  28. Cont…. • Disadvantages • High initial cost • Water must be very clean (clogging of emitters) • Requirement of higher design and management and maintenance

  29. DRAINAGE • Removal of excess water from the field/ crop root zone is termed as drainage • Importance • Facilitate ploughing and planting • Drainage lowers underground water table so as to facilitate increase root zone depth • Increase soil aeration • Avoid toxicities due to lack of air • Organic matter decomposition • Favor growth for soil organisms • Leaches excess salts

  30. Methods of drainage (1) Surface drainage • Excess surface water is removed from the cropped area by a network of surface drains • Network of drains include • Field drains • Lateral drains • Main drains (2) Subsurface drainage • In this method the soil profile water is removed by underground perforated pipe drains or tile drains Can use natural drainage lines when making drains

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