Project Number: 5310-61000-014-00
Project Type: Appropriated

Start Date: Jan 09, 2007
End Date: Jan 08, 2012

Objective:
Objective 1. Develop improved understanding and quantitative descriptions of the effects of degraded irrigation waters on root water uptake and soil hydraulic properties. Objective 2. Develop improved knowledge and predictive capabilities of unsaturated flow and transport processes affecting retention, transformation, and transport of pesticides, pathogens, pharmaceuticals and other contaminants.

Approach:
Measurements of compensatory uptake are needed to formulate improved models of root water uptake. We will conduct greenhouse studies aimed at observing compensatory uptake in cotton for different stress conditions. Cotton is deep rooted, has high salt tolerance, and is an agronomically important crop in San Joaquin Valley, CA. In the past cotton has been observed to exhibit some compensatory behaviors, e.g. utilizing shallow groundwater to varying degrees depending upon root zone conditions. Current guidelines for degraded water use are based on the effects of sodium and salinity on the soil saturated conductivity, and do not consider the impact on unsaturated hydraulic properties. Experimental data for the unsaturated properties is sparse and contradictory. To aid in the formulation of improved guidelines for irrigating with degraded waters, we propose experiments aimed at elucidating the effects of saline-sodic irrigation water on unsaturated soil hydraulic properties. The HYDRUS software will be expanded to include features that enhance its suitability as an advanced simulation model and decision support tool for testing and implementing site-specific soil, water and crop management practices. Among the features to be added are modules to account for the transport of pesticides, pathogenic microorganisms, colloids, pharmaceuticals, and related constituents in unsaturated soils. Planned modifications include improved representations of straining processes, colloid aggregation, colloid transport in unsaturated soil, size exclusion in structured soils, colloid-facilitated transport, and chemical reaction, sorption, and degradation processes. Formerly 5310-61000-009-00D (5/07).