Agronomic research on crop response to nitrogen fertilizer suggests that a plateau function may be appropriate, but the plateau varies across fields and years. Available models that treat the plateau as a stochastic variable are not readily extendable to handle field or year random effects as seems to be appropriate based on the agronomic data. This article develops a method of estimating a response function with a stochastic plateau that can capture random effects. The method is then used to determine economically optimal levels of nitrogen fertilizer for wheat (Triticum aestivum). Copyright 2008, Oxford University Press.

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Few farmers use futures markets in spite of theoretical research that says they should and educational efforts to get them to do so. This paper sought to determine the factors that explain why a sample of Indiana farmers use futures markets. Survey results showed that on average futures markets were perceived to both reduce risk and increase income. The most important factors explaining the use of futures markets were the individual's perception of the ability of futures markets to reduce risk and the individual's debt position.

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Background: Plasma a-melanocyte-stimulating hormone (a-MSH) and adrenocorticotropin (ACTH) concentrations in horses vary with season, confounding diagnostic testing for pituitary pars intermedia dysfunction (PPID).Hypothesis: The goals of this study were to determine whether seasonal variation in plasma a-MSH and ACTH concentrations in horses is influenced by geographic location, breed, or PPID.Animals: Healthy light breed horses residing in Florida, Massachusetts, and Finland (n 5 12 per group); healthy Morgan horses (n 5 13); healthy ponies (n 5 9) and horses with PPID (n 5 8).Methods: Monthly plasma a-MSH and ACTH concentrations were measured by radioimmunoassay. Nonlinear regression analysis was used to estimate the time of peak hormone concentrations. Mean hormone concentrations in fall and nonfall months were compared.Results: The fall peak plasma a-MSH concentration occurred earlier in horses residing at more northern locations. Mean seasonal a-MSH concentrations were similar in all healthy groups at all locations, but in the fall, plasma ACTH concentrations were higher in horses living in more southern locations. Plasma ACTH but not a-MSH concentrations were higher in Morgan horses compared with light breed horses from the same location. Hormone concentrations of ponies did not differ from those of horses during either season. Concentrations of both hormones were high in the fall compared with the spring in horses with PPID.Conclusions and Clinical Importance: These findings suggest geographic location of residence and breed may affect the onset, amplitude, or both of the seasonal peak of pars intermedia (PI) hormones and should be considered when performing diagnostic testing for PPID. Horses with PPID maintain seasonal regulation of PI hormone output.

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