ABSTRACT
Summary A simulation model for estimating yield of leys from standard meteorological observations is described. It is based on an S-shaped growth curve also accounting for phasic development and regrowth depression. Effects of temperature, radiation, and soil moisture are accounted for by a growth index. Soil moisture is simulated with a standard water budget. The parameters in the model were estimated by comparing measured with calculated growth. The model then predicted final harvest with reasonable accuracy, but with underestimate of early season growth, presumably due to mobilization of carbohydrate from storage organs. Observed ley yields from 49 Swedish parishes (1961-1978) were correlated with model calculations, showing a correlation coefficient of r = 0.9. North of lat 59°N the model underestimated the first hay cut, while south of this line, yields were overestimated. For the second cut the deviations were reversed. This geographical pattern suggests more assimilate storage and subsequent mobilization in northern regions with longer and more severe winters than in southern regions with milder winters.
