Impact of diverse pastures and reduced nitrogen inputs on dairy pasture yields, botanical composition and soil health across three regions

Abstract

Pastoral farmers can enhance productivity and minimise environmental impacts by utilising a range of management practices on farm. Different pasture management options being explored for their potential benefit to the farm and wider ecosystem include the use of diverse pasture species and targeted fertiliser nitrogen (N) inputs. On each of nine dairy farms across Waikato, Canterbury and Otago, one paddock was sown with a pasture mix containing perennial ryegrass/white clover/plantain (simple) and an adjacent paddock sown with an additional 12 species (diverse). Half of each paddock received either standard or low N fertiliser inputs. Herbage yields were determined for three years, with pasture species composition assessed seasonally. Soil health was assessed annually using measures of soil fertility, organic matter, physical condition and biological abundance. Total annual pasture yields were no different between the simple and diverse pastures. Pasture growth tended to be reduced in response to lower N fertiliser inputs, although results were not significant. The most consistent pasture responses to N were seen in Canterbury under irrigation. Under low N inputs there was a small increase in white clover (>1%), and although non-significant still created the potential for
increased biological N2 fixation. Plantain declined during the study from 20±2.7% to 2±0.8% in both pasture types. Grass contributed over half of the pasture sward. Although ryegrass was the dominant species in both pasture types, diversity remained higher within the diverse sward in the final year of study, with other grass species contributing up to 20±1.8% of the pasture sward. There was no effect of pasture type, N rate, or their interaction on any measured soil health property.