Sward Species Diversity Impacts on Pasture Productivity and Botanical Composition Under Grazing Systems

This research investigated the effect of intensive grazing on the annual and seasonal yield and botanical composition of three sward types: (1) Lolium perenne monoculture sward receiving 250 kg nitrogen (N) ha⁻¹ year⁻¹ (PRG 250 N); (2) Lolium perenne—Trifolium repens sward receiving 125 kg N ha⁻¹ year⁻¹ (PRGWC 125 N) and (3) a multispecies sward comprising eight species receiving 125 kg N ha⁻¹ year⁻¹ (MSS 125 N). Each sward type had its own farmlet of 20 paddocks and comprising 47 cows on 18.7 ha with each group of cows remaining on the same farmlet for the 2-year study. Total yield (13,015 kg ha⁻¹ year⁻¹ of dry matter forage) did not differ among the three sward types, despite a substantial difference in chemical N fertiliser between PRG 250 N and both PRGWC 125 N and MSS 125 N. Average botanical composition of PRG 250 N comprised 994 g kg⁻¹ grasses and 6 g kg⁻¹ weeds. The PRGWC 125 N sward had 864, 134 and 2 g kg⁻¹ of grasses, white clover and weeds, respectively, while the MSS 125 N had 671, 144, 180 and 5 g kg⁻¹ of grasses, legumes, forbs and weeds, respectively. Despite considerable variation in the component species, nutritive values were relatively unaffected by sward type. Lower organic matter digestibility was observed on MSS 125 N compared to PRG 250 N and PRGWC 125 N (788, 801 and 799 g kg⁻¹, respectively). These results suggest that increasing sward diversity and reducing the use of chemical N fertiliser can maintain grass yield and nutritive value.