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United States Department of Agriculture

Agricultural Research Service

Research Project: WATER MANAGEMENT TO IMPROVE PRODUCTIVITY AND PROTECT WATER QUALITY

Location: Water Management Research

Title: Shallow Groundwater Use by Alfalfa

Authors
item Ayars, James
item Shouse, Peter
item Lesch, Scott - UNIVERSITY OF CALIFORNIA

Submitted to: Alfalfa National Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: November 8, 2008
Publication Date: December 2, 2008
Citation: Ayats, J.E. 2008. Shallow Groundwater Use by Alfalfa. California Alfalfa and Forage Symposium and Western Alfalfa Seed Conference. 115-130.

Interpretive Summary: Disposal of saline drainage water is a significant problem for irrigated agriculture. One proposal is to recycle drainage water on salt tolerant crops until the volume has been reduced sufficiently to enable final disposal by evaporation. Part of this concept will require crop water reuse from shallow groundwater; and data is needed to quantify the potential use of this groundwater by alternative crops. A column lysimeter study was used to determine the in-situ crop water use from shallow groundwater by alfalfa as a function of ground water quality and depth to ground water. The results demonstrated that up to 50% of the crop water use could be met from shallow groundwater with an electrical conductivity (EC) less than 4 dS/m, and that the potential crop water use from deeper ground water increased over the years. The columns with high salinity in the shallow groundwater experienced increased salinity in the soil profile and root zone with time, which resulted in reduced crop water use from shallow groundwater. The alfalfa yields with time in columns with EC> 2dS/m was related to the EC of the groundwater. Crop water use from shallow groundwater improved the water productivity of the crop. In areas with shallow ground water at depths < 2m and salinity < 4 dS/m there is potential for significant use of ground water by alfalfa. This will help reduce drainage requirements, improve water productivity and reduce water demands for low salinity water.

Technical Abstract: One proposal for drainage water disposal is to reuse drainage water for irrigation of salt tolerant crops until the volume has been reduced sufficiently to enable final disposal by evaporation. Part of this concept of serial biological concentration requires in-situ crop water reuse from shallow groundwater; and data is needed to quantify the potential use of groundwater by alternative crops. A column lysimeter study was used to determine the potential crop water use from shallow groundwater by alfalfa as a function of ground water salinity and depth. Lysimeters made of 45 cm diameter PVC pipe with heights of 1.8 m and 2.6 m that were supported by hydraulic pillows made of rubberized fabric pipe were used in the study. Water table depths of 1.2 and 2 m were used with the shallow ground water position being maintained by a Marriotte bottle. Crop water use was determined using one set of columns without a water table. Ground water salinity was non-saline, 2, 4, 6, 8 dS/m and was based on the Maas-Hoffman threshold value for yield loss in alfalfa. Each ground water salinity treatment was tested in the short columns (1.8 m) with 4 replications. Only the 4 and 6 dS/m ground water was used in the 2.6 m columns also with 4 replications. The results demonstrated that up to 50% of the crop water use could be met from shallow groundwater (<1.2 m) with an electrical conductivity less than 4 dS/m, and that the potential crop water use from deeper ground water (2m) increased over the years. The columns with high salinity (> 4dS/m) in the shallow groundwater experienced increased salinity in the soil profile and root zone with time, resulting in reduced crop water use from shallow groundwater. Yields decreased with time as root zone salinity increased and periodic leaching will be required for in-situ use to be a sustainable practice. The yield loss increased as ground water salinity increased. Statistical analysis of crop yield demonstrated that there was significant use of ground water with an EC of 6 dS/m for a few years.

Last Modified: 4/21/2014
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