Rice Irrigation Systems for Tailwater Management (1/7)
J.E. Hill, S.C. Scardaci, S.R. Roberts, J. Tiedeman, J.F. Williams
Introduction
Rice in California is grown using a continuous flood system. Pest management in this system often includes the use of pesticides that may subsequently contaminate drain water for downstream use. Since 1983, state regulations have required rice growers to hold pesticide treated waters within their fields to allow the pesticides to break down into nontoxic products. The length of this holding period has increased greatly since 1983 and will continue to increase, as performance goals become more stringent. Such mandatory holding periods have made it difficult for rice growers with conventional irrigation systems to operate flexibly. For example, holding water for long periods with no spillage can be a problem because water tends to build up at the bottom of the field, causing stress on the rice.
 Recent innovations in irrigation systems make it possible for rice growers to operate with greater flexibility. Three useful strategies for managing tailwater and maintaining drain water quality are: 1) recirculating systems, in which tailwater is recovered and reused for irrigation on farm or among several farms; 2) static water systems, designed for individual fields to maintain a desired water depth with no outflow of pesticide treated waters; and 3) a gravity tailwater recapture system that utilizes pipes to divert drain water to adjacent fields and bypass drains that lead to public waterways.
Dozens of recirculating, static, and gravity recapture water systems are currently in use on California rice farms. Information on the advantages and disadvantages of each system and its potential impact on water quality will allow individual growers to choose the system or combination of systems best suited to their own rice production operation.
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Comments to jayoung@ucdavis.edu