Long-term goals of reducing environmental impacts associated with agricultural activities must include economic sustainability as well as production feasibility. This study compared the potential economic and environmental impact of two specific cropping systems [wheat/soybeans (w/s) vs. selected vegetable crops with wheat/soybeans (veg/w/s)]. Profitability of w/s was lower than the veg/w/s system but demanded a smaller, less extensive resource base of labor and machinery with fewer conflicts in resource utilization rates. The PLANETOR computer program (Univ. of Minnesota) was used to analyze the potential negative environmental effects of growing a particular crop mix within these two systems. Although some of the vegetable crops exceeded the targeted soil loss tolerance value (T-value) of 3 t/ha, the weighted average of the veg/w/s system was below the target T-value for soil erosion. Analyses suggest that the profits from vegetables in the veg/w/s production more than offset the negative impacts on soil erosion and the veg/w/s system would be more economically feasible than w/s. Potential impact of pesticide leaching and runoff from vegetable production as calculated by PLANETOR was less than that from w/s. Specific cultural practices, including soil/tissue testing to manage nutrient applications, could reduce nitrogen/phosphorus movement. The veg/w/s system may offer the necessary profit margins to allow adoption of more environmentally friendly production alternative.

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A procedure to test whether or not significant differences exist in fertilizer response functions is important in the statistical analysis of experimental data. Analysis of covariance is often used in the analysis of linear functions. This paper extends the analysis of covariance procedures to quadratic and higher order least squares regression functions by applying the statistical techniques to the results of an actual experiment.