Coupling of dry matter and nutrient accumulation in forage grass

The logistic model has proven very useful in relating dry matter production of forage grasses to applied nitrogen. A recent extension of the model coupled dry matter and plant N accumulation through a common response coefficient c. The objective of this analysis was to establish the validity of the extended model for each of the three major nutrients (N, P, K), with a common coefficient c between dry matter and each applied nutrient. Analysis of variance established the validity of this hypothesis. The model accurately described response of dry matter, plant nutrient removal, and plant nutrient concentration to applied nutrient, with overall correlation coefficients of 0.9928, 0.9972, and 0.9975 for applied N, P, and K, respectively. Furthermore, the model closely described the relationship between yield and plant nutrient removal, as well as between plant nutrient concentration and plant nutrient removal, for each nutrient. This work confirmed earlier results for applied N with various grasses and established the validity of the model for applied P and K for the first time. The logistic equation is well-behaved and simple to use on a pocket calculator. It can be used to describe yields and nutrient removal in evaluation of agricultural production and environmental quality.