MODELING WEATHER EFFECTS ON NUTRITIONAL-VALUE OF GRASS-CLOVER LEYS .2. ESTIMATION AND VALIDATION OF PARAMETERS IN A MODEL FOR CHANGES IN CRUDE PROTEIN-CONTENT

Three parameters were optimized in a simulation model for weather affected change in protein content (CP) of grass and red clover. Two parameters determine the shape of the change rate function and one sets the protein content at the onset of growth. The parameters were optimized from field experiment data obtained during 1985-1988 at six sites in central and southern Sweden. The model was validated on data from mixed Jeys. The results of the optimization and validation show that the model gave more reliable results than time regressions, but individual values of the starting value of protein content (max) must be derived for each situation because of the nitrogen dynamics in the soil. Therefore, CP prediction in a particular field cannot be made without calibration sampling.