Degree Type


Date of Award


Degree Name

Doctor of Philosophy




The objectives of this research were: (1) to test different approaches to characterize the relationship between weather and corn yields and (2) to develop yield models to simulate corn yields and optimal nitrogen rates for two soil groups using historic weather data;Yield data used in this study came from 77 simple fertilizer trials which were carried out with unirrigated corn in farmers' fields in the El Bajio area of central Mexico during the period of 1962-1965;Weather characterization of the light-textured and clay-textured soil areas, into which the region of study was divided, was made according to (1) a soil moisture simulation model by which moisture stress and excess moisture were computed, (2) the amount of rainfall during critical phenological periods for both deficit and excess moisture, and (3) a plant wilting index. Several modifications were made to the soil-moisture-simulation model to adapt it to the area of study in central Mexico;The best approach to characterize weather in the light-textured soils was a plant wilting index, which is a visual method to estimate the degree of wilting in corn plants, followed by the use of rainfall and then the moisture stress index. In the clay-soils area, the weather approaches to characterize excess moisture were very similar. In both approaches, the critical period of excess moisture was found to be early during the vegetative stage of corn;Corn-yield-predicting models developed in this study were evaluated using independent yield data. Corn-yield predicting errors were 374 kg/ha and 539 kg/ha for the best models developed for the light-textured and clay-soils areas, respectively;A weighting procedure which made use of rainfall probabilities was used to determine optimum N fertilizer rates for several locations in the area of study;Corn-yield simulations for varying rooting depths and several locations using historic weather records are discussed.



Digital Repository @ Iowa State University,

Copyright Owner

Jose Francisco Villalpando-Ibarra



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201 pages