Practices and barriers for water quality improvement in California Rice

Practices and Barriers for Water Quality Improvement in California Rice

S.C. Scardaci, A.U. Eke, S.R. Goldman Smith, J.E. Hill, S.R. Roberts,
J.F. Williams, B.R. Hanson, J.D. Rhoades and M.C. Shannon 1

UC Cooperative Extension, P.O. Box 180, Colusa, CA 95932

Irrigation water must be held in rice (Oryza sativa, L.) fields for up to 30 days after a herbicide application to increase dissipation and improve public waterway water quality. Seedling establishment problems caused by salinity have been observed in some fields during the water holding period (WHP).

A field scale water quality project was established near Colusa, CA to demonstrate and assess effectiveness of recirculating, static and conventional irrigation systems for water quality improvement.

Herbicide concentration and water outflow data were collected and used to calculate molinate discharges from each system. Static and recirculating systems kept molinate discharges very low most years, while conventional systems were very low some years and higher other years depending on how water was managed.

Between 1990 and 1996 growers installed recirculating and static irrigation systems on about 75,000 ha using project assistance. From 1982 to 1996 water holding and these alternative systems reduced peak molinate concentrations in the Sacramento River by about 96%.

Rice field water salinity was highest during the water holding periods, especially in bottom basins. Salinity in some fields was high enough to cause seedling problems, while in other fields it was low and not a problem. Salinity may be a barrier to water holding in some fields.

1 UC Cooperative Extension, Colusa County; Dept. of Water Resources; Dept. of Agronomy and Range Science, UC Davis; UC Cooperative Extension, Sutter County; Dept. of Land and Water Resources, UC Davis; and U.S. Salinity Laboratory, Riverside, CA

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