2994Data and Analytical ToolsCalifornia Water Plan Update 2005Survey of Irrigation Methods in California By Morteza Orang, Richard Snyder and Scott Matyac, DWR and UC DavisCalifornia Water Plan Update 2005Volume 43004Survey of Irrigation Methods in California in 2001 Survey of Irrigation Methods in California in 2001 Morteza N. Orang1, Richard L. Snyder2, J. Scott Matyac3AbstractThis report discusses a statewide survey of irrigation methods conducted in California during 2002. The purpose of the study was to collect information on irrigation methods to determine which methods were used by growers to irrigate their crops in 2001. Reliable information on irrigation methods is an importantfactor for planning future water demand by agriculture irrigation based on trends. To conduct the survey,one-page survey form was developed to collect irrigated land (acres) by crop and irrigation method. Thena questionnaire was mailed out to 10,000 of the estimated 80,000 growers in California by the California Department of Food and Agriculture. The results from comparing earlier studies with 2001 indicated that the amount of land irrigated by drip irrigation method has increased by about 33%, while the amount of land irrigated by surface methods has decreased by about 31%. The area planted to orchards and vineyards has increased, while that planted to field crops has declined. The largest increase in sprinkler use has been in vegetable crops, an increase of 19% since 1972. The 1991 and 2001 statewide surveysexclude rice acreage.IntroductionThe application of water to soils for crop use is referred to as irrigation. Surface (gravity-driven surface irrigation), sprinkler, drip/micro, and sub-surface are types of irrigation methods that are used by growersto irrigate various crops in the state. The irrigation methods that growers use to apply water may affect the salt accumulation in the crop root zone (leaching), plant transpiration, soil evaporation, and runoff fromsoil surface. Irrigation performance is commonly measured by how much of applied water beneficiallyused for crop production. Irrigation (application) efficiency or consumed fraction is an index used to quantify the efficient use of water diverted to a field by an irrigation system and is defined as the ratio of that quantity of water stored in the root zone, which can be used in evapotranspiration to the amount ofapplied water as a percentage. Distribution uniformity (DU) is also an important element in irrigation water use efficiencies. DU is the measure of the uniformity of irrigation water distribution over a field. The most appropriate irrigation method for an area depends upon physical site conditions, the crops being grown, amount of water available, and management skill. The water management decisions stronglyinfluence how uniform water can be applied through different irrigation methods to provide optimal soil water conditions for crop growth and marketable yields. The main objectives are to avoid water stress, achieve high yields and protect water quality. Water losses from irrigation vary with the type of irrigation method. In the absence of a reliable irrigation system, the water application is often non-uniform and is generally over applied, resulting in excess runoff and deep percolation below the root zone. If part of the 1 Staff land and water use scientist, California Department of Water Resources – Division of Planning and LocalAssistance, PO Box 942836, Sacramento, CA 94236-00012 Biometeorologist, University of California, Atmospheric Science, Davis, CA 956163 Senior land and water use scientist, California Department of Water Resources – Division of Planning and LocalAssistance, PO Box 942836, Sacramento, CA 94236-00011Survey of Irrigation Methods in California3014Data and Analytical ToolsCalifornia Water Plan Update 2005 Survey of Irrigation Methods in California in 2001 field is over irrigated, the crop roots near the soil surface will be exposed to water that has salinity near that of the irrigation water rather than an average root zone soil salinity value. As a result, crop yields are generally more affected by the irrigation water salinity level than by the soil water salinity in the lower part of the root zone. However, the use of a proper irrigation method that fits the crop, water, and site conditions will ensure that losses are held to a minimum and subsequently, will result in high irrigationefficiency and distribution uniformity.Runoff and deep percolation generally are greater for gravity systems than for well managed sprinkler and drip/micro irrigation methods. The combined losses of deep percolation and runoff for poor managed gravity irrigation system will lower consumed fraction and subsequently, will pollute the surface waterand groundwater supplies. Sprinkler and drip/microsystems reduce runoff or deep percolation comparedto gravity irrigation, because these type systems provide complete control over the amount of waterapplied to the field. As a result, water is distributed more uniformly within the intended root zone.Generally, more water is used with gravity and sprinkler irrigation on an annual basis than with drip/micro. According to the “Report on Evaporation from Irrigated Agricultural Land in California” byCharles Burt of CalPoly, gravity and sprinkler irrigation tends to wet larger fractions of the soil surface (0.6-1.0, or 60%-100%, of the soil surface is wet during a typical irrigation) than drip/micro systems. In addition, it is often difficult to control the application depth of irrigation water because of uniformity and scheduling constraints. Drip/micro has typical wetted fractions ranging from almost 0, for subsurface drip, to 0.8, for some micro spray on tree crops. A typical range for trees in California is 0.3-0.6 for surface drip/micro. Drip/micro is also considered to have more flexibility for irrigation scheduling.Water resources project planning requires reliable estimates of crop and irrigation system combinations,which are important components in a variety of water budget analysis. To update California’s records onirrigation methods used within the state, a survey is conducted by the California Department of water Resources about every 10 years. The gathered survey data is analyzed and compared with earlier surveysto study how irrigation methods are changing and to make projections of future changes for long-termplanning.The purpose of this report is twofold;