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' FLOOD IRRIGATION OF ALFALFA: HOW DOES IT BEHAVE? <br />Blaine Hanson and Dan Putnam' <br />ABSTRACT <br />E ' <br />Flood irrigation is commonly used for alfalfa irrigation in the Central Valley of California, This <br />' irrigation method uses the soil surface to flow water down the field. Thus, its performance is <br />highly dependent on soil properties such as infiltration rate and surface roughness. Because these <br />properties are not known for a given field, a trial-and-error approach is used for managing these <br />systems. Discussed herein are some options for improving the system design and its <br />' management. The effect of surface runoff from flood-irrigated alfalfa fields <br />on water duality is also discussed along with measures to help reduce adverse water quality <br />effects from the runoff. <br />Key Words: alfalfa, irrigation, flood irrigation, border irrigation, water quality, pesticide <br />' runoff' <br />INTRODUCTION <br />' Alfalfa is a major crop grown in California, with about 1 million acres in production. Alfalfa is <br />primarily used for dairy feed, however some alfalfa is used by the horse industry. Because of the <br />climate in California, alfalfa must be irrigated to obtain maximum production. The main <br />' irrigation method in California is flood irrigation, which flows water.across the soil from the <br />upper end of the field to the lower end. Fields are divided into checks separated by borders. <br />Sprinkler irrigation is used to a lesser degree, although in the intermauntan region of northern <br />California, it is the primary irrigation method. <br />IRRIGATION SYSTEM CHARACTERISTICS <br />' Border or flood irrigation flows a sheet of water across the field. The advantage of this method is <br />that it is inexpensive, both in terms of system costs and energy costs. The disadvantage is that its <br />performance depends strongly on soil properties such as the infiltration rate. It is the most <br />' difficult irrigation method to manage efficiently because of its dependence on soil properties and <br />its performance characteristics, and thus, a trial-and-error approach is normally used in its <br />management. <br />' Border or flood irrigation designs have several common features. They usually have slopes <br />from 0.1% to 0.2%, include small `border checks' (or small levies) 6-20" high, which confine <br />water to an area from 10 to 100 feet wide so that water moves down the field. Field length in the <br />direction of flow varies, but is usually determined by field constraints and soil characteristics. <br />' 113. Hanson, Irrigation and Drainage Specialist, Dept. of Land, Air and Water Resources, University of California, <br />Davis, One Shields Ave., LAWR, Davis, CA 95616; D. Putnam, Associate Agronomist, Dept of Agronomy and <br />Range Sciences, One Shields Ave, Davis, CA 95616; Email: brhanson(a3ucdavis.edu; dhputnamQucdavis.edu. 1n: <br />Proceedings, National Alfalfa Symposium, 13-15 December, 2004, San Diego, CA, UC Cooperative Extension, <br />¦ University of California, Davis 95616. (See http://at(aifa.ucdavis_edu for this and other proceedings). <br />88