Optimising land and fertiliser N usage in grassland systems where grazing and conservation areas are separate

Abstract

In grassland systems where grazing and conservation areas are separate, the farmer must decide on the N rates to use in the two areas and on the proportion of the total area to devote to conservation. Quantified relationships between N supply and herbage yields, and estimates of DM requirements, were used to determine the optimum split of total area for cutting and grazing and the N rates to be used to maximise stocking rate for a fixed total fertiliser N usage, or to minimise N usage for a fixed stocking rate. Results indicated that the optimum split of area was around 70% grazed, 30% cut for conservation, with higher N rates on the cut area than on the grazed area. The method also allowed estimates to be made of the economic optimum fertiliser N usage and stocking rate.