Date of Award

8-2015

Degree Type

Thesis

Degree Name

Master of Science

Major

Environmental and Soil Sciences

Major Professor

Brian G. Leib, Hubert J. Savoy

Committee Members

Donald D. Tyler

Abstract

Understanding the effect of supplemental irrigation and timing of nitrogen availability on yield of cotton is pertinent to the success of Tennessee cotton producers. Response to irrigation and nitrogen source is likely to vary across greatly differing soil types. This research indicated the need for higher amounts of water and earlier irrigation initiation to optimize yields in coarse-textured, low water holding capacity soils. Deep silt loam soils did not respond to irrigation in two wet years. Delaying nitrogen availability via use of a polymer coated urea fertilizer generally either lowered or did not affect yield. Delaying nitrogen availability was less detrimental to yield in coarse-textured soils, but was not a superior method to supply crop nitrogen demand.

Soil sampling is the foundation for addressing a field’s nutrient status and possible need for fertilization. Proper fertilization is economically and agronomically attractive, as well as environmentally responsible. To facilitate precision nutrient management, sampling methods are needed to more precisely define nutrient variability than a field average. We looked at techniques for grid sampling, delineation of management zones, and optimal intensity of cores necessary. Grid sampling is a popular method for diagnosing in-field nutrient variability, but is time consuming. We found grid-point sampling to capture more variability across a field than grid-cell sampling, agreeing with the majority of previous research. Delineation of management zones was successful in grouping nutrient variability using soil maps of varying scale and yield maps. A sampling intensity of 2-8 cores/acre was optimal.

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