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United States Department of Agriculture

Agricultural Research Service

Title: Field Soil Hydraulic and Solute Transport Measurements As a Function of Water Pressure Head

Authors
item Casey, Francis - IOWA STATE UNIVERSITY
item Logsdon, Sally
item Horton, Robert - IOWA STATE UNIVERSITY
item Jaynes, Dan

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 5, 1998
Publication Date: N/A

Interpretive Summary: Concerns with the presence of agricultural chemicals in groundwater have drawn attention toward the processes of chemical movement in field soil. We used field methods to help us understand how water and chemicals move in soil. These methods specifically measure how water and chemicals move rapidly through certain regions of the soil, and how chemicals are retained in other regions of the soil. This study combined characterization of water movement with characterization of chemical movement through soil. Knowledge of these processes is essential to understand contamination of groundwater by chemicals moving through the soil. These results will be of interest to soil hydrologists active in research, modeling, and regulatory activities.

Technical Abstract: Concerns with the presence of agricultural chemicals in groundwater have drawn attention toward the processes of chemical transport in field soil. The hydraulic and preferential flow properties of a soil play an active role in the transport of chemicals to groundwater. In this study the hydraulic conductivity (K) and preferential flow parameters (immobile water content and mass exchange coefficient) and the mobile/immobile domain model were investigated by using a recently described in situ technique. Forty field measurements were made within a no-till field mapped as a Harps series soil, a fine-loamy, mixed mesic Typic Calciaquoll. The immobile water contents and immobile water fractions were not significantly different at the head (h) values of -150, -60, and -30 mm. The median immobile water fraction values were 0.40, 0.28, 0.25, and 0.40 for the respective water heads of 10, -30, -60, and -150 mm. The mass exchange coefficient values were positively correlated to h and K. The median mass exchange coefficient values were 0.59, 0.015, 0.0028, and 0.0030/hour for h values of 10, -30, -60, and -150 mm, respectively. Also some correlations were found between macroscopic capillary length and immobile water fraction, which may suggest some break between the macropore and mesopore solute transport domains. The values for immobile water content and mass exchange coefficient were similar to previously reported values.

Last Modified: 4/23/2014
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