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Improved Knowledge and Modeling of Water Flow and Chemical Transport Process in Irrigated Soils


<OL> <LI> Develop improved understanding and quantitative descriptions of the
effects of degraded irrigation waters on root water uptake and soil hydraulic
<LI>Develop improved knowledge and predictive capabilities of unsaturated
flow and transport processes affecting retention, transformation, and transport of
pesticides, pathogens, pharmaceuticals and other contaminants.

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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).

Skaggs, Todd; Shouse, Peter
USDA - Agricultural Research Service
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