GRAZING SIMULATION-MODEL - GRASIM .B. FIELD TESTING

A comprehensive grazing simulation model, GRASIM, that links all compo nents of the pasture system was developed. The model predicts growth r ate, water drainage, nitrogen leaching, and factors affecting animal i ntake. In order to ensure validity of the simulation field testing of GRASIM was conducted using local experimental data. These tests were a lso performed for better parameter estimation. Field testing and evalu ation of GRASIM components, grass growth, nitrogen, and water budget t o central Pennsylvania conditions is presented. The model was tested f or 1993 and 1994 and two fertilizer treatments-with and without animal manure. Statistical tests indicated a good fit between predicted and observed data for accumulated biomass, nitrate leaching and amount of water drained. Because of the mechanistic nature of the GRASIM, the mo del did not require any calibration. The model can be used in its pres ent form by researchers, extension personnel, and trained farmers to i ncrease the efficiency of pasture use.