COUPLING OF DRY-MATTER AND NITROGEN ACCUMULATION IN RYEGRASS

The logistic model has proven very useful in relating dry matter produ ction of warm season perennial forage grasses to applied nitrogen. A r ecent extension of the model coupled dry matter and plant N accumulati on through a common response coefficient c. The objective of this anal ysis was to apply the extended logistic model to cool season Gulf annu al ryegrass (Lolium multiflorum Lam.) and to establish a common respon se coefficient c between accumulation of dry matter and plant N. Analy sis of variance established the validity of this hypothesis. The model accurately described response of dry matter, plant N removal, and pla nt N concentration to applied N, with an overall correlation coefficie nt of 0.9954. Furthermore, the model closely described the relationshi p between yield and plant N removal, as well as between plant N concen tration and plant N removal. The logistic equation is well-behaved and simple to use on a pocket calculator. It can be used to estimate yiel ds and plant N removal in evaluation of agricultural production and en vironmental quality.