Estimating a Two Nutrient Yield Response Surface From University Extension Information.

Most university Extension recommendations for nutrients treat each nutrient separately. Such an approach has historically been acceptable because nutrient prices have been low relative to other inputs. However, in recent years, prices of some nutrients have escalated to levels not historically seen. Current recommendations do not provide the necessary decision-making process to help farmers allocate their fertilizer dollars across nutrients to maximize net returns. In an attempt to begin moving nutrient recommendations in this direction, a mathematical approach was developed for estimating the coefficients of a quadratic yield response surface. Input data came from university Extension publications. Key pieces of information were: rates recommended from a sufficiency approach, soil test calibration data, and state/regional average maize yield responses to nitrogen rates. Economically optimum combinations of two nutrients were calculated for various nutrient price combinations using the estimated response surface.