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United States Department of Agriculture

Agricultural Research Service

Research Project: Impact of Degraded Waters on Soil Physical and Chemical Properties
2013 Annual Report


1a.Objectives (from AD-416):
To develop information on the impact on soil physical and chemical properties when using degraded and saline waters for irrigation and determine predictive relationships based on statistical analysis of lab and field experiments.


1b.Approach (from AD-416):
To conduct laboratory and field research as needed to determine the impact of degraded and saline waters on physical and chemical properties of California soils. Documents SCA with University of California-Riverside.


3.Progress Report:

The project is also related to objective 2 of the parent project, "Improve our ability to predict the impact of degraded waters on infiltration into soils and plant response to irrigation with these waters by a) determining the impact of using degraded waters for irrigation, including the effect of solution chemistry, high dissolved organic matter, and application of organic wastes, on soil physical and chemical properties". We completed an experiment to evaluate the changes in infiltration rates of a soil with smectite clay from the Central Coast when irrigated with waters of increased SAR and pH. We examined a range of sodium adsorption ratios between 0-10, and pH between 6 and 9. We utilized a wetting and drying sequence to simulate field conditions, including rain via a rain simulator. Previous infiltration experiments examining these variables have been with non swelling clays. The patterns of sensitivity to increased sodium adsorption ratio (SAR) were comparable to the other soils tested with decreases in infiltration observed even at sodium adsorption ratios as low as 2. We initiated an additional infiltration study utilizing the same experimental facility, setup and experimental design, only in this instance with a low pH soil, also a swelling clay from the Central Coast area near Paso Robles. Despite the fact that the soil pH remained low even after the one year experiment, there was an adverse effect of SAR, as expected and also elevated pH of the irrigation water. Infiltration is limited by the surface crust, that responds rapidly to the chemical conditions of the irrigation water.

We conducted an experiment to evaluate the changes in unsaturated hydraulic conductivity related to solution chemistry. We are measuring water content as related to soil matric stress and well as sorptivity and then calculating the unsaturated hydraulic conductivity. Direct measurement of unsaturated hydraulic conductivity at low water contents is very time consuming, difficult and subject to large experimental error. The limited literature available on this subject was based on experiments that did not consider the effect of pH on hydraulic conductivity nor adequately characterize the initial chemical conditions. We have established that elevated pH results in increased water content at low matric pressures, as does elevated SAR, confirming that elevated pH results in a decrease in the number of large water conducting pores and an increase in smaller pores, thus likely adversely impacting infiltration and unsaturated hydraulic conductivity. These results compliment the infiltration studies and the known literature on saturated hydraulic conductivity.


Last Modified: 7/30/2014
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