Adaptation and evaluation of the integrated farm system model to simulate temperate multiple-species pastures

Whole-farm simulation provides a tool for predicting the effects of farm management strategies on farm productivity and profitability. One such model, the Integrated Farm System Model (IFSM), was modified to allow representation of up to four forage species coexisting in a pasture mixture. The model was calibrated to simulate net herbage accumulation (NHA) observed during six periods of a 2002 experiment in a 3-species pasture in Pennsylvania, USA, composed of orchardgrass (Dactylis glomerata L.), white clover (Trifolium repens L.), and chicory (Cichorium intybus L.). The model also predicted sward botanical composition, total annual NHA, crude protein (CP), and neutral detergent fiber (NDF). Sensitivity analysis showed that predictions of NHA were most sensitive to both chicory and orchardgrass specific leaf area and partitioning of photosynthate to the shoot, as well as chicory photosynthetic efficiency. The model was evaluated against data from the same 3-species pasture in 2003 as well as a 2-species pasture (lacking chicory) from the same experiment in 2002 and 2003. Predictions of total annual NHA in 2- and 3-species pastures were within ±18% of observed values, though predictions of within-season NHA were less accurate. Predictions of botanical composition tended to remain within ±15% of observed values by species. Predictions of within-season CP and NDF concentrations in the whole sward tended to remain within ±22% and ±15%, respectively. Given the generality and realism required of IFSM, the degree of precision in the modified pasture submodel is acceptable for achieving IFSM's primary goal of comparing the effects of different management scenarios on forage productivity and the long-term profitability and environmental impact of farms.