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Title: FIELD DETERMINATION OF SOIL HYDRAULIC AND CHEMICAL TRANSPORT PROPERTIES

Author
item AL-JABRI, SALEM - IOWA STATE UNIVERSITY
item HORTON, ROBERT - IOWA STATE UNIVERSITY
item Jaynes, Dan
item GAUR, ANJU - IOWA STATE UNIVERSITY

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2002
Publication Date: 6/14/2002
Citation: AL-JABRI, S.A., HORTON, R., JAYNES, D.B., GAUR, A. FIELD DETERMINATION OF SOIL HYDRAULIC AND CHEMICAL TRANSPORT PROPERTIES. SOIL SCIENCE. 2002. V. 167(2). P. 353-367.

Interpretive Summary: To determine the fate and transport of water, nutrients, and other agricultural chemicals applied to fields, scientists need basic information about the hydraulic and chemical properties of soils. However, current methods for measuring these soil properties are costly and slow, which prevents the routine collection of this valuable data and limits its availability. We developed and tested a new approach for simultaneously measuring both soil hydraulic and chemical transport properties with a simple, rapid measurement system that is adaptable for use in the field. Our findings showed that the new method is easy to use, reproducible, and provides measurements that are equal in accuracy to current, more expensive and time consuming techniques. The new method will be of interest to other soil scientists and technicians and should lead to greater availability of critical soil information for scientists, regulators, and others.

Technical Abstract: Hydraulic and chemical transport properties are the major inputs in predictive models that simulate the movement of water and chemicals through the vadose zone. However, there is a lack of field measurements of such properties to verify models describing water and chemical movement through the soil. One of the objectives of this study was to use a point source method to determine simultaneously the hydraulic and chemical transport properties at multiple field locations. A second objective was to determine the spatial distribution of such properties across a field. A total of 50 field locations within a 7 x 15-m area were rapidly and simultaneously evaluated for such properties. The hydraulic properties were the saturated hydraulic conductivity (K) and the macroscopic capillary length (L). The chemical transport properties were the immobile water fraction and the mass exchange coefficient alpha. The hydraulic properties were determined by applying three discharge rates from irrigation dripper lines and measuring the resultant steady-state flux densities at the soil surface beneath each emitter. The chemical transport properties were determined by applying a sequence of three conservative tracers at a steady-state infiltration rate and measuring their resident concentration in the soil. The K values ranged from 7.5 to 79.0 cm hr**-1, with a median of 27.4 cm hr**-1. The L values ranged from 0.03 to 13.1 cm, with a median of 2.6 cm. The immobile water fraction values ranged from 0.36 to 0.88, with a median of 0.57. The alpha values ranged from 0.002 to 0.12 hr**-1, with a median of 0.034 hr**-1. The values of the hydraulic and chemical transport parameters were found to be comparable with values reported by studies conducted on nearby field locations on similar soil. Based on semivariogram analysis, the measured properties were not spatially correlated. Because the method required only 2 days to collect data it should prove useful for future studies that require extensive field measurement of hydraulic and chemical transport properties.