cientists from the U.S. Department of Agriculture, California Department of Water Resources, University of California and other agencies are working side by side with a Fresno State researcher in the study of drainage water reuse on the west side of California’s San Joaquin Valley.

Of the many specialists involved in the work, Fresno State plant science professor Sharon Benes is in her third year tracking the growth and water use (ET) of highly salt-tolerant plants called halophytes. She is completing a report on specific research funded by the California Agricultural Technology Institute (CATI) in 1998-99. Her study focused on the growth of saltgrass (Distichlis spicata) irrigated with saline drainage water, also containing high levels of boron and selenium.

The West Side San Joaquin Valley has been for years an agriculturally rich area. However, soil salinity and drainage problems are common. West-side soils tend to be saline, and salinity problems are exacerbated by slowly-permeable soils and a high water table which often prevents successful leaching of salts. The shallow saline groundwater contributes salts to the root zone because as the soil dries at the surface, water and salts move upward via capillary flow. Only freshwater is evaporated and the salts stay behind. Boron can also accumulate in this manner. Over time, both the salts and boron can accumulate to concentrations that are inhibitory, or even toxic, to crop growth.

An environmentally responsible system for drainage water management is to use the water for irrigation in a sequential reuse system that applies the saline drainage to progressively more salt tolerant crops and finally to halophytes as the drainage becomes progressively concentrated in salinity through reuse.

Benes’ study has focused on the saline water use of saltgrass and other halophytes; and there is some good news: The saltgrass appears to be thriving under irrigation with drainage water about two-thirds the salt content of sea water and high in boron. The research is focused specifically on the amount of water the saltgrass is using daily, which is about 60 percent of the water use of a common fescue grass irrigated with high quality (nonsaline water). "That’s pretty good water usage, in our opinion," Benes stated in regard to the figures.

The saltgrass water use was determined by growing it in lysimeters, custom-made from the bottom of a 55-gallon drums are fitted with a leak-proof drainage line, filled with sand and buried so the plants growing in the lysimeter are level with the surrounding soil surface. The lysimeters are irrigated from a tank and all drainage is returned to the source tank. Water use of the saltgrass is obtained by measuring the volume of water required to re-fill the source tank each day. That water volume is compared to the reference ET (ETo) published by the California Irrigation Management Information System (CIMIS) which represents the water use of a well-watered, turfgrass (fescue) under non-saline conditions.

There is much work to be done in the area of drainage water reuse, Benes said. Additional salt tolerant forages and halophytes need to be evaluated for growth and water use under irrigation with the Westside drainage water. Research results will be used to guide the selection of the most appropriate crop and plant species for on-farm, drainage water reuse and management. Soil management methods must also be developed because over the long-term, applications of high sodium drainage water will degrade the physical structure of the soil and reduce water infiltration in the reuse areas. Proper use of soil amendments such as gypsum will be critical to maintain soil quality in these fields.

Benes and her colleagues provided details of their work at a series of workshops around the valley during May and June. Complete details also may be obtained from her report to be published by CATI this fall. It will be made available on the CATI Internet web site at cati.csufresno.edu. Single hard copies also may be requested by using the publications available form on Page 7.