Water Conservation, Reuse, and Recycling Proceedings of an Iranian-American Workshop (2005) / Chapter Skim
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Pages 79-93
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From page 81... ...
81 Optimal Irrigation: Considerations for Semiarid Regions John Letey Irrigation is required for high crop productivity when precipitation is inadequate to meet the crop evapotranspiration (ET) demand.
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From page 82... ...
82 WATER CONSERVATION, REUSE, AND RECYCLING causing yield reduction in those underirrigated areas. Conversely, if irrigation is programmed to recharge the storage capacity for those zones that have the lowest infiltration rate, the other parts of the field will be excessively irrigated leading to unrecoverable water lost to deep percolation.
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From page 83... ...
OPTIMAL IRRIGATION: CONSIDERATIONS FOR SEMIARID REGIONS 83 the optimal management scheme for a given irrigation system. Unfortunately, measurement of uniformity is complex.
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From page 84... ...
84 WATER CONSERVATION, REUSE, AND RECYCLING extract water from the soil and transfer it to the leaf surfaces at a rate equal to the transpiration rate, the plant can grow at its potentially highest rate. If the rate of transfer of water from the soil through plant tissue to the leaf surface is less than the plant's loss of water by transpiration, the plant responds by closing stomata to reduce the water loss.
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From page 85... ...
OPTIMAL IRRIGATION: CONSIDERATIONS FOR SEMIARID REGIONS 85 farmer can grow a crop and apply a small amount of water resulting in very low crop production. Farmers can also grow a crop for high production and either eliminate runoff or capture runoff and use it as part of the irrigation supply.
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From page 86... ...
86 WATER CONSERVATION, REUSE, AND RECYCLING FIGURE 1 The relationships between relative yield of cotton lint and the amount of deep percolation to the amount of infiltrated water for different irrigation uniformities as depicted by Christiansen uniformity coefficient (CUC) values.
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From page 87... ...
OPTIMAL IRRIGATION: CONSIDERATIONS FOR SEMIARID REGIONS 87 from the root zone must be applied. The amount of water to be applied, however, depends on the salinity level of the irrigation water and the crop sensitivity to salinity.
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From page 88... ...
88 WATER CONSERVATION, REUSE, AND RECYCLING FIGURE 2 Relationships between relative yield of corn and cotton and the amount of infiltrated waters of different salinities. Numbers on curves refer to electrical conductivity (EC)
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From page 89... ...
OPTIMAL IRRIGATION: CONSIDERATIONS FOR SEMIARID REGIONS 89 FIGURE 3 The total benefit (TB) and average benefit (AB)
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From page 90... ...
90 WATER CONSERVATION, REUSE, AND RECYCLING benefits or costs associated with deep percolation are borne by the farmer, they become externalities. With externalities, the economically optimal management from the perspective of the farmer may not be economically optimal from a social perspective.
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From page 91... ...
OPTIMAL IRRIGATION: CONSIDERATIONS FOR SEMIARID REGIONS 91 (ha cm) of IW and is not affected by the cost of water.
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From page 92... ...
92 WATER CONSERVATION, REUSE, AND RECYCLING out the state to form a California Irrigation Management Information System (CIMIS)
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From page 93... ...
OPTIMAL IRRIGATION: CONSIDERATIONS FOR SEMIARID REGIONS 93 CONCLUSIONS Many factors contribute to the selection of the irrigation system and management. The scientific and economic principles are well established and can be used to select the optimal set of options.
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