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Document Type

Thesis - University Access Only

Award Date

1998

Degree Name

Master of Science (MS)

Department / School

Agricultural Engineering

First Advisor

Darrell W. DeBoer

Abstract

Demand and competition for water has increased the desire for water conservation in the world. Drip irrigation, a relatively new and popular irrigation technology, has the potential to increase conservation of valuable water resources in irrigated agriculture. A field evaluation of a Green-Ampt based, drip irrigation theory (Chu, 1994) was conducted on a Renshaw sandy loam, a Brandt silty clay loam and an Estelline clay loam soil near Brookings, South Dakota. Field data consisting of wetted radii and maximum wetted depths under surface emitter discharges of 1, 2, 3, and 4 L/h were used to define soil wetted patterns. Undisturbed soil water samples were used to estimate saturated hydraulic conductivity, bulk density and initial water contents. The field and laboratory data sets in conjunction with Chu's theory were used to obtain field estimates of two Green-Ampt soil parameters, the water content parameter (M) and the pressure potential parameter (H). Initial soil water contents were near field capacity values because of unusual rainfall prior to the tests. Thus, the field tests were conducted under soil water conditions wetter than normally associated with irrigation events. Water content parameter (M) values were not affected by emitter discharge but were influenced by soil type where the Brandt silty clay loam produced the highest value and the Renshaw sandy loam the lowest value. Likewise, pressure potential (H) values were not affected by emitter discharge but were affected by soil type where the Brandt silty clay loam and the Estelline clay loam values were similar to each other but were higher than the Renshaw sandy loam value. Soil type had minimal affect [sic] on the change of wetted radii versus time in the field. However, emitter discharge had a pronounced impact on wetted radii versus time relationships with the smallest radii associated with the smallest discharge at a given time after irrigation initiation. Ratios of maximum wetted depths and radii were not affected by emitter discharge but were affected by the soil type. The Renshaw sandy loam had the highest wetted depth to wetted radius ratio of the three soils while the Brandt silty clay loam had the lowest. A ratio of 1.38 for the Renshaw sandy loam soil indicated that the wetted depth was 1.38 times larger than the wetted radius. In contrast, a representative ratio of 0.88 for the Brandt silty clay loam indicated that the wetted depth is only 0.88 of the wetted radius value. Comparison of field and theoretical (Chu' s model) results were interesting. Chu' s model produced good agreement (5 % representative coefficient of variation, cv, value) between measured and estimated radii for the Estelline clay loam, fair agreement (10 % cv value) for the Renshaw sandy loam and poor agreement (15 % cv value) for the Brandt silty clay loam soil. The model produced estimated maximum wetted depths that were about 20% less than the field depths for the Renshaw sandy loam soil, about 5% less for the Estelline clay loam soil and about 25% more for the Brandt silty clay loam soil.

Library of Congress Subject Headings

Microirrigation
Microirrigation -- Mathematical models -- Evaluation

Format

application/pdf

Publisher

South Dakota State University

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