COUPLING OF DRY-MATTER AND NUTRIENT ACCUMULATION IN FORAGE GRASS

The logistic model has proven very useful in relating dry matter produ ction of forage grasses to applied nitrogen. A recent extension of the model coupled dry matter and plant N accumulation through a common re sponse coefficient c. The objective of this analysis was to establish the validity of the extended model for each of the three major nutrien ts (N, P, K), with a common coefficient c between dry matter and each applied nutrient. Analysis of variance established the validity of thi s hypothesis. The model accurately described response of dry matter, p lant nutrient removal, and plant nutrient concentration to applied nut rient, with overall correlation coefficients of 0.9928, 0.9972, and 0. 9975 for applied N, P, and K, respectively. Furthermore, the model clo sely described the relationship between yield and plant nutrient remov al, as well as between plant nutrient concentration and plant nutrient removal, for each nutrient. This work confirmed earlier results for a pplied N with various grasses and established the validity of the mode l for applied P and K for the first time. The logistic equation is wel l-behaved and simple to use on a pocket calculator. It can be used to describe yields and nutrient removal in evaluation of agricultural pro duction and environmental quality.