MODELING ANIMAL AND FORAGE RESPONSE TO FERTILIZATION OF ANNUAL RANGELANDS

The response functions for forage, animal gain, and stocking rate were estimated from data obtained in a three-year fertilization experiment on California annual range. Degree-days; the interactions between degree-days and nitrogen, between degree-days and phosphorus-sulphur, and between nitrogen and phosphorus-sulphur; and the lagged forage variable were significant in explaining the variations in forage growth, animal gain, and stocking rate. The impact of PS was more important in interaction with DD or N than by itself. The correct impact of moisture was not found due to misspecification of the variable in the model. The models for the first year and the three years combined were well behaved; however, the models for the last two years combined neither explained adequately nor behaved well.Livestock Production/Industries,

Breeding resistant alfalfa holds promise for silverleaf whitefly management

Since 1991, the silverleaf whitefly has caused serious damage to alfalfa production in the southern desert region. Reports from the Imperial County Agricultural Commissioner suggest that direct and indirect effects of the whitefly have caused average forage yields to decrease by 17%. Recently developed plant-breeding procedures are proving successful in developing genetic resistance to this insect. We expect to have adapted cultivars with silverleaf whitefly resistance available to growers by 2000

MODELING ANIMAL AND FORAGE RESPONSE TO FERTILIZATION OF ANNUAL RANGELANDS

The response functions for forage, animal gain, and stocking rate were estimated from data obtained in a three-year fertilization experiment on California annual range. Degree-days; the interactions between degree-days and nitrogen, between degree-days and phosphorus-sulphur, and between nitrogen and phosphorus-sulphur; and the lagged forage variable were significant in explaining the variations in forage growth, animal gain, and stocking rate. The impact of PS was more important in interaction with DD or N than by itself. The correct impact of moisture was not found due to misspecification of the variable in the model. The models for the first year and the three years combined were well behaved; however, the models for the last two years combined neither explained adequately nor behaved well