Validation of SPUR2.4 rangeland simulation moldel using a cow–calf field experiment

SPUR (Simulation of Production and Utilization of Rangelands) is a grassland ecosystem simulation model. SPUR2.4 output was compared with 29 years of cow–calf data from a field experiment conducted in north-central Texas, USA. Simulated primary productivity for C-4 shortgrass was good, adequate for C-4 mid-grass and live C-3 wintergrass but inadequate for total wintergrass. The productivity of C-3 annual grass predicted by the model was of the same order of magnitude as productivity measured in the field and appears to be adequate in terms of predicting secondary production. Between-season herbage standing crop and long-term persistence were simulated adequately for individual soils but not for areas containing more than one soil series. The model gave accurate simulations of weaning weight per hectare for both the purebred Hereford and Charolais-cross animals for all grazing treatments and intensities. However, the lack of ability to simulate accurately with more than one soil per grazing unit must be corrected before the model will adequately simulate secondary productivity for landscapes that contain different soil series.