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United States Department of Agriculture

Agricultural Research Service

Title: Irrigating Forage Crops with Saline Waters 2. Modeling Root Uptake and Drainage

Authors
item Skaggs, Todd
item Shouse, Peter
item Poss, James

Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 10, 2006
Publication Date: June 21, 2006
Citation: Skaggs, T.H., Shouse, P.J., Poss, J.A. 2006. Irrigating forage crops with saline waters 2. modeling root uptake and drainage. Vadose Zone Journal. 5:824-837.

Interpretive Summary: The disposal of agricultural drainage waters into surface waters or onto lands leads to salinization and degraded soil and water quality. The recycling of agricultural drainage water for irrigation is increasingly viewed as a desirable management practice in areas with limited options for drainage disposal. Modeling is potentially a cost-effective approach to examining design and management options for drainage reuse systems, but questions exist about the accuracy of simulated root water uptake in dynamic, highly saline conditions such as encountered in reuse operations. This study compared HYDRUS-1D simulations of root water uptake and drainage with lysimeter data collected during an experiment in which forage crops (alfalfa and tall wheatgrass) were irrigated with synthetic drainage waters. The results will benefit scientists and engineers interested in crop growth and water use under saline soil conditions, as well as scientists and engineers working on the design and management of agricultural drainage reuse systems.

Technical Abstract: The recycling of agricultural drainage water for irrigation is increasingly viewed as a desirable management practice in areas with limited options for drainage disposal. Modeling is potentially a cost-effective approach to examining design and management options for drainage reuse systems, but questions exist about the accuracy of simulated root water uptake in dynamic, highly saline conditions such as encountered in reuse operations. This study compares HYDRUS-1D simulations of root water uptake and drainage with lysimeter data collected during an experiment in which forage crops (alfalfa and tall wheatgrass) were irrigated with synthetic drainage waters. A trial-and-error fitting procedure was used to determine uptake reduction parameters for each crop. Good agreement between the model simulations and data was achieved, a noteworthy result given the broad range of experimental conditions considered: irrigation waters with salinities ranging from 2.5 to 28 dS/m and irrigation rates ranging from deficit to luxurious. It does not seem possible at this time to derive uptake reduction parameters from published salt tolerance data, meaning the near term prospects for using this model in a purely predictive capacity (i.e., without crop- and site-specific calibration) are limited. Nevertheless, it is clear the modeling approach captures many essential features of root water uptake under stressed conditions and it may be useful in designing and analyzing reuse operations.

Last Modified: 12/19/2014
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