Doctoral Dissertations

Date of Award

8-2003

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Biosystems Engineering

Major Professor

Ronald E. Yoder

Committee Members

John B. Wilkerson, Daniel C. Yoder, James A. Larson

Abstract

Variability of soil properties in many fields is too great for a whole field to be effectively managed with a uniform application of irrigation water. Consequently, a decision must be made for irrigation management about which areas in the field should be treated differently or grouped. A decision-making framework was developed to determine whether site-specific irrigation management would be cost effective for selected fields. The framework is designed to find the best field layout in terms of water management, and tests the hypothesis that there is a particular field management layout that maximizes net return. As part of the framework, a merging algorithm recursively combines adjacent sub-areas with differing soil units until the whole field is merged into one management unit. The decision-making procedure creates different field layouts; the selection of the best layout is then based on an economic analysis. There is a trade off between increased yield and gross returns with the increased costs associated with the site-specific irrigation. There may exist a layout somewhere between the maximum number of divisions (completely site-specific irrigation) and complete grouping (uniform irrigation) that maximizes profit. The general framework was applied to a field in Cocke County, Tennessee that had been intensively soil mapped. Five different soil types in the field made up six different potential soil-management units. From the soil mapping information, six different management layouts were created. A site-specific irrigation schedule based on 31 years of climate data and a yield response equation were used in the analysis. A yield estimation function was used with the assumption of maximum yield; water stress was the only yield-reducing factor that was considered. Average tomato prices for the years of v the analysis were corrected for the price base of 2001, the last year of the analysis. The water applied in each layout was dependent on the year of analysis. The average water applied was not significantly different for the layouts (P>0.73). However, the expected average tomato production was dependent on the layout, and was significantly different for site-specific irrigation as compared to uniform irrigation of the entire field (P<0.0001). The decision-making framework with the merging algorithm identified the layout (layout 4, net annual average return = $282,282) that maximized profit, as compared to uniform irrigation (layout 6, net annual average return = $238,433). In the completely site-specific management layout (layout 1), the yield increase compared to layout 4 was negligible, and the increased costs to treat each management unit individually decreased the return (net annual average return = $281,352).

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