Optimal nitrogen and choice of reduced tillage systems for wheat production in north western Oklahoma.

摘要

Scope and method of study. Simulation data from the Erosion Productivity Impact Calculator Model (EPIC) and enterprise budget elaborated from the Oklahoma State University Budget Generator were used to study the long-term onsite and offsite effects of soil erosion on wheat production in Garfield County, Oklahoma. It was assumed that the farm has six soil types, and in each, the producer would choose for each of the 100 years of the planning period, a level of nitrogen application and one of four possible tillage systems. The study estimated the functions of erosion, yield, nitrogen carryover, and nitrogen loss functions per soil type. A discrete dynamic economic model was used to determine the private and social optimum rate of nitrogen application and choice of reduced tillage systems under different assumptions of market prices of wheat and nitrogen, cost of erosion and nitrogen loss, and discount rates. Because of the complexity inherent in using dynamic programming for this problem, the study developed a branching method, which is a simpler approach to solving for the optimal solution.;Findings and conclusions. It was found that the optimal tillage system was different from private versus social choice. The optimum rates of applied nitrogen were almost identical for the sweep systems, varying from 117 kg/ha to 132 kg/ha across all soil types. The corresponding rates were slightly higher for disk chisel. They varied between 124 kg/ha and 135 kg/ha. The plow system required much higher rates of nitrogen application that vary from 136 kg/ha to 145 kg/ha. The net present value of the disk chisel was higher than the other tillage systems for private optimization, and the net present value of sweep system twice was the highest for social optimization where the farmer is responsible for offsite damage costs of soil erosion. The optimal choice of tillage systems and resulting nitrogen application was not sensitive to changes in wheat and nitrogen prices, and discount rates for either private or social optimization. However, the optimum tillage sequence was sensitive to changes in the cost of erosion and nitrogen loss. A 50% reduction in these costs would make farm shift from using sweep systems to using disk chisel. The results imply that policies aimed at reducing soil erosion are bound to be less effective without internalizing the cost of offsite damages.