Experimental evaluation of a crop growth simulation model. A case study with rhodes grass

The crop growth simulation model BACROS describing production under optimum conditions of water and nutrient supply, is tested with data collected in field experiments with Rhodes grass (Chloris gayana Kunth). The choice of specific parameters for the plant species is discussed and special attention is paid to stomatal behaviour. It was concluded that in all situations examined (climate room, greenhouse and field), stomatal aperture was determined by the CO₂ concentration inside the stomatal cavity and hence by the rate of assimilation. Measured and calculated rates of assimilation, respiration and transpiration of an artificial sward showed good agreement. In the field situation the maximum rate of dry matter accumulation was predicted with reasonable accuracy as was the rate of water use. Initial growth rates and the rate of growth towards the end of the growing period showed deviations. The former inaccuracies were associated with the death of tillers, the latter with the formation of flowering stems.