ESTIMATING REGIONAL CROP YIELDS IN SWEDEN WITH A SIMULATION-MODEL ANDFIELD OBSERVATIONS

Yields of barley were predicted for four agricultural districts in cen tral and southern Sweden during the years 1988-92. An observed time tr end was corrected for yearly weather effects as predicted by the Europ ean multicrop model WOFOST. Effects of pest damage estimated from smal l plot experiments with pesticides, and from general large-scale area surveys, were included. Original model parameters were used to predict barley emergence and phenological development, but a parameter for th e relative growth rate of leaf area in the model was reduced. Predicti ons of yields for SKO-areas (approximately 30 x 30 km, Statistics Swed en) with the same soil- and plant model parameters, were overestimated in central and underestimated in southern Sweden. Compiling all yield data correlation coefficients, I, for predicted versus observed yield s ranged from 0.62 to 0.71, with no conclusive differences between are a definition, method for calculation or method for estimating pest dam age. Regressions as measured by r were improved when both weather and pest damage were considered. The root mean error of prediction (RMSEP) was also reduced, when both weather and pest damage were considered.