MODELING TALL FESCUE CULTIVAR RESPONSE TO APPLIED NITROGEN

Models can be used to estimate yields and nutrient utilization by fora ge grasses. The objective of this study was to model response of three cultivars of tall fescue (Festuca arundinacea Schreb.) to applied N o ver a 3-yr period at Watkinsville, GA. The procedure uses analysis of variance to evaluate linear parameter A and the exponential parameters b and c for the logistic equation. It was shown that yields could be averaged across Sears and that all differences among cultivars could b e assigned to the b (intercept) parameter. 'AU-Triumph' proved to be m ore efficient at converting sail N to dry matter without applied N tha n either 'Johnstone' or 'Kentucky 31' cultivars. Endophyte (Acremonium coenophialum Morgan-Jones and Gams) infection did not affect dry matt er response relationships of Kentucky 31. Maximum incremental conversi on of applied N to dry matter occurred at N = 125 kg ha(-1), where pla nt N utilization was approximate to 80%. The logistic model provides a very useful tool for evaluating response of tall fescue cultivars to applied N.