A NITROGEN-PHOSPHORUS-POTASSIUM MODEL FOR FORAGE YIELD OF BERMUDAGRASS

A logistic equation was used to relate annual dry matter yield of Coastal bermudagrass [Cynodon dactylon (L.) Pers.] to applied N, P, and K. Yield data from a 4 X 4 X 4 (N X P X K) factorial experiment were analyzed. The second order Newton-Raphson procedure for nonlinear regression was used to estimate the seven parameters of the model. A correlation coefficient of 0.9884 was obtained with the model for the 64 data points. A response surface for yield as related to N and K at P = 100 kg ha-1 was drawn from the model. Isoquants (constant yield) were drawn for annual yield of 10 Mg ha-1. A residuals diagram showed no trends, lending further validity to the model. These results have application to agricultural production and environmental quality.