Date of Award:

5-1975

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Department name when degree awarded

Soil Science and Biometeorology

Committee Chair(s)

D. W. James

Committee

D. W. James

Committee

R. L. Smith

Committee

H. B. Peterson

Abstract

In the Zapotitan Valley near San Andres, El Salvador, Central America, an experiment was conducted to determine the availability of residual soil N to corn grown during the rainy season. This was an extension of an experiment conducted during the preceding dry season. The variables of the dry season experiment were irrigation method, crop, and rate of fertilizer N application. Soil NO3-N and NH4-N were determined by soil sample analysis to a soil depth of 120 cm by 30 cm depth increments. The samples were taken at the end of the dry season experiment and again at harvest time of the wet season experiment. Yield of corn grown during the rainy season was measured. The results indicate the following: (1) soil NO3-N alone was an efficient indicator of residual soil N; (2) there was a linear increase of soil NO3-N with N applied four months previously at the beginning of the dry season crops; (3) soil sampled to the 30 cm depth was sufficient to estimate availability of the residual N; (4) corn yields increased linearly with the increase of soil NO3-N; (5) the measurement of residual soil NO3-N can be used as a soil text index in connection with N prediction equations for estimating fertilizer N requirements. The measurements of soil NO3-N can, therefore, increase the efficiency of fertilizer use in a wet-dry tropical climate.

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