Crop yield response models and fertilizer applicators' efficiency.

摘要

The objective of the first essay is to explain the source of increases in yield and improvements in the efficiency of nitrogen use in Cotton ( Gossypium hirsutum L.) production. Cotton yield has gone up while the nitrogen recommendation per bale has trended down. Sources of increased yield have mostly been credited to improved genetics and pest management. The linear stochastic plateau response function was estimated for each of five variety groups and the economically optimal rate of nitrogen was determined for each group. The results show an increasing slope, which indicates an increased efficiency in nitrogen utilization, and an increasing plateau, which implies improvements in yield potential.;In the second essay, the Bayesian method is used to estimate a wheat yield response function using a stochastic plateau model. The objective is to extend the stochastic plateau functions by relaxing the normality assumption for the plateau random effect. The beta distribution was chosen so that the plateau can exhibit either right or left skewness. The economically optimal rate of nitrogen is determined using the plug-in approach, which is commonly used in the literature and the Monte Carlo optimization technique. The plug-in method ignores the parameter uncertainty, which might affect the accuracy of the nitrogen recommendation. The results indicate that the normal plateau model fits the wheat data better than the beta distribution. In addition, the plug-in method results on average in 0.6% lower nitrogen recommendation than the Monte Carlo approach.;The objective of the third essay is to examine the profitability of the fertilizer application activities at farm supply cooperatives and to examine how profitability is affected by equipment utilization, size of trading territory, and competition in the trade area. The results indicate that profitability increases with the number of applicators, but did not show any clear pattern relative to applicator utilization. Profitability increases with number of branches but then fell for the cooperatives with the highest number of branches.