Grazing and Soil Fertility Effect on Naturalized Annual Clover Species in New Zealand High Country

With a view to increasing rangeland pasture legume abundance, the herbage biomass and seedling recruitment of four New Zealand naturalized annual clover species (haresfoot clover Trifolium arvense L., suckling clover T. dubium Sibth, cluster clover T. glomeratum L., and striated clover T. striatum L.) were measured in relation to spring grazing deferment versus continuous grazing and low versus high superphosphate fertilizer application (5 vs. 9 kg P · ha-1) at a midaltitude (700-m) hill site. Naturalized species were dominant over periodically sown white (T. repens L.) and subterranean clover (T. subterraneum L.), contributing > 90% to sward legume composition. Rainfall in spring-early summer varied greatly between years, driving the large variation in sward legume content (28% in the moist first year; 2% in the very dry second year). Grazing deferment in spring did not influence autumn seedling recruitment or the following spring herbage biomass of naturalized species. However, autumn recruitment of naturalized clovers was greater under low fertilizer (563 seedlings · m-2) compared with high fertilizer application (271 seedlings · m-2) in the second year of the study, suggesting a niche for these species under conditions of low soil P and S. Management efforts should focus on strategies to enhance naturalized species spread within NZ rangeland.