Effect of nitrogen fertiliser applications on botanical composition

The diminishing returns associated with nitrogen (N) fertiliser use over time are well recognised, as are the detrimental effect to the environment of excess N fertiliser use (Eckard 1998). However, many Tasmanian dairy farmers apply continually high rates of N fertiliser (e.g. in excess of 500 kg/ha annually) to minimise risk associated with variable pasture dry matter (DM) yields, and this often occurs at the expense of white clover populations within the pasture (Frame 1990; Frame et al. 1998). The responses of botanical composition and perennial ryegrass DM yields to N fertiliser application rate were investigated in the current field plot study, to provide further information for farmers about the production-related effects of their N use.