Tuesday, November 14, 2006

Maximizing Root Water Uptake from a Shallow Saline Groundwater Resource.

Peter Shouse, USDA-ARS U.S. Salinity Lab., 450 W Big Springs Rd., Riverside, CA 92507-4617, James Ayars, USDA-ARS, 9611 S. Riverbend Ave., Parlier, CA 93648-9757, and Richard Schoneman, USDA ARS Water Management Research, 9611 S. Riverbend Ave, Parlier, CA 93648.

Irrigated agriculture uses between 60 and 80% of the fresh water resource, and the competition of this resource is becoming acute.  It is evident, that agriculture will be forced to use increasing quantities of degraded water, in part to offset reductions in fresh water allocation and in part to reduce waste water disposal impacts.  As an alternative water source for crop production, saline shallow groundwater use would reduce both fresh water requirements and drainage water disposal.  Our purpose for this research is to determine optimum irrigation strategies for maximizing water use from the shallow groundwater, and to determine the effects of major system variables to shallow groundwater uptake.  We installed 27 0.3 m dia. by 1.8 m long  weighable soil columns with TDR for measuring water content, and Marriott bottles for controlling and measuring water table depth.  We planted alfalfa (medicago?).  Once established, we irrigated the columns with good quality water at the measured ET rate and varied the depth to groundwater and the groundwater quality.  We found that there were large differences in alfalfa productivity do to water table depth and increased salinity of the groundwater above a threshold limit.  We also found that significant amounts of water uptake occurred from the shallow groundwater between irrigations.  This implies that bey controlling irrigation frequencies we may be able to optimize the groundwater contribution to crop water requirements.