ESTIMATION OF YIELD AND NITROGEN REMOVAL BY CORN

A wide variety of mathematical models have been used to relate crop production to management factors such as applied Ei and water availability These include power functions and exponential functions. The objective of this analysis was to use an extended logistic model to relate dry matter yields and plant N removal to applied N for corn (Zea mays L.) for three soils in North Carolina. In this model, response of both dry matter yield and plant N removal to applied N were described by logistic equations. Plant N concentration was then related to applied N by the ratio of these logistic equations. Model parameters were estimated by nonlinear regression. Analysis of variance showed that the N response coefficient c was common for dry matter yield and plant N removal for each soil. Overall correlation coefficients of yield and plant N removal with applied N were very high for all three soils (R > 0.99). It was shown that approximate to 50% of the total dry matter and 80% of total plant N were contained in the grain at all applied N levels. Maximum potential grain yield of 25.9 Mg ha(-1) agreed closely with an estimate in the literature of 26.5 Mg ha(-1) (500 bushels acre(-1)). Dependence of plant N concentration on plant N removal was shown to follow a Linear relationship. The present model provides a rational basis for coupling of dry matter yield and plant N removal in response to applied N. It can be used in design and management decisions related to agricultural production and environmental quality.