The effects of stocking rate and nitrogen fertilizer on a perennial ryegrass‐white clover sward

Abstract

Abstract Four stocking rates (25–55 sheep ha −1 ) and two N fertilizer treatments (nil or 200 kg N ha −1 ) were imposed on swards containing perennial ryegrass ( Lolium perenne ) and white clover ( Trifolium repens ) which were continuously stocked throughout one grazing season. These treatments gave swards that varied greatly in their content of white clover. The effects of these treatments on pasture and animal performance in the following season were examined when all plots were continuously‐stocked with 25 yearling sheep ha −1 and received no N fertilizer. There was slight regeneration of clover in the second year. Herbage growth ranged from 5.4 to 11.0 t dry matter (DM) ha −1 , was closely correlated with the clover content of the swards and was higher on swards that had previously received 0 rather than 200 kg Nha −1 . The liveweight gain and wool production of sheep in the second grazing season closely reflected the herbage growth and clover content of the swards. As a result, animal production was greatest from swards which had previously been stocked at the lowest rate and had received no N fertilizer and least from swards which had been stocked at the lowest rate but had received N fertilizer. The results show that the adverse effects of over‐grazing and N fertilizer application in one season may be partially rectified by lower stocking rates and by withholding N fertilizer in the following season.