Prediction of forage yield from simulated soil moisture deficits

Abstract

A simplified soil moisture budgeting model was developed. The sensitivity of the soil moisture budgeting model to the method used for the calculation of potential evapotranspiration (PET), actual evapotranspiration (AET), and soil moisture movement was evaluated. Using the soil moisture budgeting model as a basis, a forage yield prediction model was also developed. Four methods for quantifying plant water stress were used to determine soil moisture deficit factors for critical growth periods. Stepwise multiple regressions were used to produce prediction equations from these factors. Data for calibration and validation of the models were obtained from the Santa Rita Experimental Range in southeastern Arizona. The PET method employed had a negligible effect, however, the AET method selected was important to soil moisture estimation, with the more complex methods giving the most accurate results. The soil moisture budgeting inodel explained 85 percent (r=0.92) of the variation in observed values over the period of calibration and 64 percent (r=0.80) of the variation in observed values over the period of validation. The forage prediction model explained 85 percent (r=.92) of the variation in average perennial grass production over the period of calibration, but produced essentially no correlation over the period of validation.