|Soppe, Richard - UC DAVIS|
Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 19, 2002
Publication Date: October 4, 2002
Interpretive Summary: Increased ground water use will reduce the irrigation demand for fresh water, and will result in less production of drainage water from tile drained fields. Salinization of the root zone is often associated with an increase in shallow, saline ground water use. Crop use of shallow ground water depends on many factors, including the depth to the water table, soil hydraulic characteristics like water holding capacity and hydraulic conductivity, evapotranspiration demand, the root growth and distribution of a crop, and salinity and toxicity levels in both soil water and the ground water. A study was conducted to measure the volume of ground water that a safflower crop can use. The study measured soil water content at multiple depths in the root zone to determine at what depth ground water and salts move into the root zone. Results from the study are that once the safflower crop is fully developed ground water use can be up to 40% of daily crop water needs. Over the complete growing season, 25% of crop water need can be provided by saline ground water. Ground water is used at the bottom of the root zone, thus creating deposition of salts at the bottom of the root zone, but minimizing transport of salts into the root zone.
Technical Abstract: Two weighing lysimeters with and without shallow saline ground water were used to measure crop evapotranspiration of surface drip irrigated safflower. A saline water table (14 dS/m) was maintained in one of the lysimeters. Ground water use as part of crop evapotranspiration was characterized using hourly measurements of the water level in a ground water supply tank (Mariotte bottle). Ground water contribution of up to 40% of daily crop water use was measured. On a seasonal basis, 25% of the total crop water use originated from the ground water. The largest ground water contribution was shown to occur at the end of the growing season, when roots are fully developed and stored soil water in the root zone is depleted.