|Salinity Studies in Rice -
Project Leader and Principal UC Investigators
Stephen R. Grattan, extension plant-water relations specialist, Department of Land, Air and Water Resources, University of California, Davis
Steven C. Scardaci, University of
California Cooperative Extension farm advisor, Colusa/Yolo/
Stacey R. Roberts, postgraduate researcher, UC Cooperative Extension
James E. Hill, extension agronomist and chair, Department of Agronomy and Range Science
William K. Thomas, postgraduate researcher, UC Cooperative Extension
|UC scientists completed a three-year
study of salinity problems in the Sacramento Valley and, as a result, are recommending a
lowering of the thresholds used to predict damage.
Reports of reduced rice yields due to salinity was verified by a survey of 27 grower fields in Colusa and Glenn counties conducted between 1993 and 1995. The problem stems from irrigation practices, such as static flow and recirculating systems, intended to reduce herbicide concentrations in tailwater runoff. Unfortunately, these irrigations methods appear to be concentrating salts as well.
Rice is extremely sensitive to salinity during seedling and early development. Yields are reduced by a decrease in seedling stand and poorer plant growth. Current salinity guidelines are based on limited research and indicate that crop yields are reduced 12 percent for every unit of electrical conductivity above 3.0 deci-Siemens/meter (dS/m). The electrical conductivity of water is an indicator of the salinity hazard. However, preliminary data gathered in the survey suggested that yields were affected by salinity at even lower levels. Climate and environmental factors are known to affect salt tolerance, so field salinity experiments were begun in 1996 to modify the guidelines for the Sacramento Valley.
The salinity experiments were conducted at a site in Colusa County. Researchers used five-foot-diameter aluminum rings in 28 salinity plots. Small plots 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 in these plots ranged from 0.3 (grower field) to 11.9 dS/m., increasing in direct proportion to salt content in field water.
El Ni±o injected an element of variability in test results. Unlike the first two years of the experiment, last yearÆs data did not show a profound influence from increasing levels of salinity on the number of tillers per plant or the number of plants and tillers in a given area. Similarly, salinityÆs effect on grain yield was not as great as it had been the previous years. However, 1998Æs unusual weather had an enormous influence on stand establishment, growth and how salinity affected rice performance. For example, late spring rain left standing water up to four inches deep in the plots, not only diluting salinity but also reducing stand densityin all treatments. Cool early season and hot late summer weather also affected rice development. On the other hand, salinity consistently reduced biomass and yield by delaying tillering and reducing individual grain weight.
Results from all three years of the study strongly suggest that a salinity threshold of 1.9 dS/m would be more appropriate for the Sacramento Valley. This is consistent with the results of the earlier survey and a greenhouse study conducted by the U.S. Salinity Laboratory.