Salinity Studies in Rice-97


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Project Leader and Principal UC Investigators

Stephen R. Grattan - Extension Plant-water Relations Specialist Department of Land Air and Water Resources UC Davis

Steven C. Scardaci - University of California Cooperative Extension Farm Advisor Colusa/Yolo/Gletin counties

Stacey R. Roberts - Postgraduate Researcher UC Cooperative Extension

William Y. Thomas - Postgraduate Researcher UC Cooperative Extension

James E. Hill - Extension Agronomist and Chair, Department of Agronomy and Range Science

UC scientists are continuing their investigation of irrigation practices that have helped reduce herbicide concentrations in tailwater runoff but appear to be creating salinity problems for some rice growers in the Sacramento Valley.

In a survey of 27 grower fields conducted between 1993 and 1995, researchers from the University of California and the USDA/ARS Salinity Lab gathered strong evidence that salinity is reducing rice yields in several areas of Colusa and Glenn counties. They believe that recent irrigation innovations such as static flow and recirculating systems increase the potential for field salinization by allowing salts to concentrate in lower basins.

Rice is known to be very sensitive to salinity. Current guidelines for rice indicate that crop yields can be reduced by 12 percent for every increase in unit of electrical conductivity above 3.0 deci-Siemens/meter (dS/m). Electrical conductivity is a direct reflection of salt concentration in water. However, current guidelines may be inadequate. Information gathered from the earlier survey showed that yields were affected by soil salinity level in excess of only 2.0 dS/m and seedling establishment was adversely affected at even lower levels. Since climate and environmental factors are known to affect salt tolerance, researchers felt it necessary to conduct field salinity experiments in the Sacramento Valley to modify guidelines for the area.

Researchers conducted a second year of testing in a salinity experiment at the same location in Colusa County. They established 28 salinity plots with five-foot diameter aluminum rings. Small plots such as this are necessary not only because salinity plots require numerous measurements and intense management but also because the amount of salt needed to establish and maintain large-scale plots would be prohibitive.

The time-averaged electrical conductivity ranged from 0.4 to 11.9 dS/m. Small increases in salinity had a profound influence on stand establishment and overall plant density. Moderate levels of salinity delayed tillering. However, the number of tillers per plant increased with increasing salinity up to 7 dS/m. This helped to offset the devastating effect salinity had on stand establishment.

Salinity also reduced shoot and root biomass, as well as grain yield. Salinity reduced grain yield primarily by reducing the number of panicles per area, as well as by reducing individual grain size. Researchers also found that salinity delayed heading but did not appreciably increase the percent of sterile florets - as it did in 1996.

A statistical analysis of observations recorded in 1996 and 1997 indicates that threshold salinity guidelines should be lower than they are currently. However, scientists feel an additional year of research is necessary to increase confidence in a firm recommended guideline. In the interim, they suggest a tentative threshold of 2 dS/m be used in water policy decisions regarding salinity standards or for water allocations.

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