Sward species diversity impacts on pasture productivity and botanical composition under grazing
Abstract
As part of the management of intensive grazing, the focus on simple and productive forage systems has led to a limited range of plants being used in grazing swards supported by high levels of chemical fertilisers. This study investigated three different combinations of plant diversity and N fertiliser level (perennial ryegrass monoculture (PRG), 250 kg N ha–1; two-species perennial ryegrass-white clover (PRG-WC), 125 kg N ha–1; eight-species containing grasses, clovers and herbs (MSS), 125 kg N ha–1). Each sward type had its own farmlet of 20 paddocks and comprised 50 dairy cows on 20 ha which were rotationally grazed. Over two years, botanical composition of the PRG-WC was composed of 836, 163 and 1 g (kg DM)–1 of grasses, white clover and unsown species, respectively; MSS had 673, 151, 171 and 5 g (kg DM)–1 of grasses, clovers, herbs and unsown species respectively. Total net herbage production (13 022 kg ha–1 year–1 of DM forage) and nutritive values were unaffected by sward type during the 2 years. These results suggest that increasing sward diversity while reducing the use of chemical N fertiliser can maintain herbage production and nutritive value.