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<br />," <br /> <br />COO'lG? <br /> <br />. <br /> <br />Field Irrigation Efficiency <br /> <br />Field irrigation efficiency has been defined for this study as: <br /> <br />Fi Id" ff = Actual crop evapotranspiration <br />e urlg. e , f <br />Volume 0 water delivered to field <br /> <br />Several factors which affect field irrigation efficiency are discussed in <br /> <br /> <br />the following paragraphs, Some of these can be altered by management <br /> <br />and others can not. Two specific types of losses which decrease the field <br /> <br /> <br />efficiency and which may be altered by management are those of deep per- <br /> <br /> <br />colation below the root zone and surface runoff from the field. <br /> <br />Soil type <br /> <br />Perhaps the most influential factor affecting the field irrigation <br /> <br /> <br />efficiency, and which is generally only slightly alterable by management, <br /> <br /> <br />is the soil type. Two very important soil properities are involved. <br /> <br />. <br /> <br />Soil water-holding capacity, The ability of the soil to hold water <br /> <br /> <br />available for plant uptake is determined by the texture and the soil <br /> <br /> <br />depth. In general, sandy soils have low, loam soils high, and clay soils <br /> <br />intermediate available water-holding capacities. Typical values expressed <br /> <br /> <br />as inches of available water per foot of soil are given in Figure 1. When <br /> <br /> <br />the soil has a low capacity for holding water, due either to texture or <br /> <br /> <br />depth, there is a much greater potential for loss of water by deep perco- <br /> <br /> <br />lation. The irrigation application requirement must necessarily be low, <br /> <br />and the ability of the irrigator to apply the correct amount without <br /> <br /> <br />excessive leaching is considerably more difficult regardless of the appli- <br /> <br /> <br />cation method used, Essentially nothing can be done to alter the water- <br /> <br /> <br />holding capacity of a soil. <br /> <br />. <br /> <br />-5- <br />