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f <br /> De artment ®f Water ter Res'.)rces <br /> California Irrigati®n Management Information System <br /> Crop Coefficients (Kc) Explained <br /> Crop coefficients (Kc)are used with ETo to estimate specific crop evapotranspiration rates. The <br /> crop coefficient is a dimensionless number(usually between ,1 and 1.2)that is multiplied by the <br /> ETo value to arrive at a crop ET(ETc)estimate. The resulting ETc can be used to help an irrigation <br /> manager schedule when an irrigation should occur and how much water should be put back into <br /> the soil.An example calculation follows: <br /> If, ETo = 0.25 inches/day (for July 15, 1985) and, Kc = 0.55for-an orange tree in <br /> then, ETc = ETo x Kc = 0.25 inches/day x 0.55 = 0.1375 or 0.14 inches/dayF- July) <br /> 1 <br /> Crop coefficients vary by crop, stage of growth of the crop,and by some cultural practices. Citrus <br /> trees have smaller coefficients than peach trees (when the peach tree is at full cover). Coefficients <br /> for annual crops (row crops)will vary widely through the season,with a small coefficient in the early <br /> stages of the crop(when the crop is just a seedling)to a large coefficient when the crop is at full <br /> cover(the soil completely shaded). Almond orchards with cover crops between tree rows will have <br /> larger coefficients than almond orchards without cover crops. <br /> t <br /> It is very important to understand that the crop coefficients that should be used with CIMIS ETo <br /> (with grass as the reference crop)are those that were developed specifically for use with <br /> grass-referenced ETo. <br /> , <br /> The University of California Cooperative Extension has prepared two leaflets on crop coefficients: <br /> Leaflet#21427- "Using Reference Evapotranspiration (ETo) and Crop Coefficients to Estimate <br /> Crop Evapotranspiration (ETc) for Agronomic Crops, Grasses, and Vegetable Crops" and Leaflet <br /> #21428- "Using Reference Evapotranspiration (ETo) and Crop Coefficients to Estimate Crop <br /> Evapotranspiration (ETc)for Trees and Vines".-These crop coefficients are designed for use with <br /> CIMIS'ETo information. These leaflets are available by contacting <br /> CIMIS Help Line <br /> (800) 922-4647 <br /> Department of Water Resources <br /> WaterEfficiency Office <br /> P.O. Box 942836 I <br /> Sacramento, CA 94236-0001 <br /> l <br />�I <br /> I � <br /> ' Notice last modified on March 24,2001 <br /> For more information,visit www.cimis.water-ca.gov <br /> J ' <br /> y <br />