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? >N 9 t•'k.l.y, `; z Yr� f "L5t„1*E f F�� ra,�aol kt �� .,' bh a + +t z 1"4 ,.�� „� a� w e'+f,:y ,�k� ' �• sy � 'k a� i�l� �� t Ih � s�"s � t 9 S 5 a �t N �� `F r P. ✓y,", are��{,�i�. � e t�.a[U` k�'y�}y.c7, i� P � � r :.;, � t PqthC Y y Steven C. Scardaci Michael C. Shannon Stephen R. Grattan Austine U. Eke Stacey R. Roberts S. Goldman-Smith James E. Hill Water management practices in California rice production can affect salinity in the field. This is particularly important because rice Grown in flooded conditions, is one of the most sensitive crops to rice is one of the most salinity. We extensively monitored sensitive crops to salinity. salinity patterns In dozens of rice In California,rice is generally grown in a series of basins,with water running from upper to lower basins before fields in Colusa and Glenn counties, draining out.The authors found that salinity stress and yield reductions tend to increase in order to determine how salinity from upper basins,above,to bottom basins,below. varies from basin to basin and to compare salinity patterns under different irrigation systems. We feature called aerenchyma (large internal about 60%more than inflow water. By found that the fields most air spaces),which provide oxygen to the early 1990s, rice growers were hold- vulnerable to salinity damage were roots,allowing the plant to thrive un- ing water in basins for up to 30 days those with higher soil salinity and der flooded conditions.Most weed spe- (May to early June) after a pesticide ap- using irrigation water sources cies cannot survive in this environment. plication (Lee et al. 1993).These hold- initially high in salinity, particularly Unlike other crops,rice is seeded di- ing periods were the primary means of nondistrict sources that are rectly into saturated fields by aircraft, reducing pesticide residues and were combinations of well and drain providing a uniform stand.Historically, required by the state Department of most rice has been grown using a con- Pesticide Regulation to fulfill the Cen- water. Long water holding periods, ventional"flow-through" system where tral Valley Regional Water Quality while effective in reducing pesticide Irrigation water flows sequentially Control Plan,Rice growers adopted concentrations in rice fields, can through a series of basins starting at the closed systems,which recirculate water contribute to salinity increases in top and ending at the bottom.Weirs be- within basins,or constructed static wa- bottom basins. Salinity can increase tween basins control water depth and ter basins,in which water flows into a with either conventional or static flow,and excess water in the bottom ba- single basin without an outflow.They irrigation management systems, but sin spills into a drainage ditch. also developed gravity systems,in the salinity pattern in the field will Water management practices in Cali- which drainage water from the bottom be different. fornix rice production have changed basin bypasses the drain by redirecting substantially since the 1970s and early it to the top basin of another series of More than 470,000 acres of rice 1980s, when water was held in the field lower-elevation basins. were planted in California in for short periods of several days.In the During the late 1980s and early 2001,with a production value of early 1970s,water quality studies in 1990s California experienced a long- $138 million (according to the Califor- California indicated that the salinity of term drought, resulting in further tail- nia Agricultural Statistics Service). Rice rice-field outflows averaged about 30% water outflow restrictions and a is different from the state's other im- higher than inflow water in 14 fields no-spill policy,which prohibited the portant field crops in that it is grown in (Henderson et al. 1974).In five fields discharge of field water from bottom basins under continuously flooded con- from COILIsa and Glenn counties,the basins into waterways after June 30 or ditions,Rice has a unique anatomical salinity of outflow water averaged July 15 (1992 to 1994) in some rice- 184 CALIFORNIA AGRICULTURE,VOLUME 56,NUMBER 6