Does modelling of spatial heterogeneity matter?
The presence of grazing animals contributes to a much greater spatial heterogeneity in the cycling of C and N within grasslands, compared to arable land. This is primarily due to the deposition of excreta in patches rather than evenly over the field. However, an additional source of heterogeneity is introduced because grazing animals do not evenly utilise the grassland. Herbage contaminated by their faeces will tend to be rejected, as will poor quality (low digestibility) vegetation. There is therefore good reason to expect that C and N cycling will be highly spatially variable in grazed grassland. Hitherto, grassland models have assumed C and N dynamics to be uniform within a field. In this paper, modelling is used to investigate the potential effect of spatial heterogeneity on the estimated C sequestration and N emissions in grazed grassland. The FASSET farm model (www.fasset.dk) was modified to describe the dynamics of spatial heterogeneity in grassland. For each day that the grassl
