Seedling recruitment response of New Zealand-naturalised annual clovers to superphosphate fertiliser in summer dry high country grassland

Abstract

Pasture legume presence in low-input, extensively-grazed grassland areas is vitally important for provision of nitrogen inputs and quality herbage. Traditionally sown legume species such as Trifolium repens lack longevity in summer dry (<800 mm annual rainfall) environments. Greater abundance and persistence of less-researched naturalised annual clover species Trifolium dubium, Trifolium glomeratum, Trifolium arvense, and Trifolium striatum has been observed in New Zealand dry hill country and upland grasslands. At a mid-altitude (~700 m a.s.l.), sunny-facing, moderately steep, high country grassland site in summer dry Central Otago, NZ, naturalised annual clover species contributed the largest proportion of legume sward content (>90%) while sown species, Trifolium repens and Trifolium subterraneum, contributed the least (<10%) over two years. Autumn seedling recruitment of naturalised annual clover species was measured in response to low (75 kg ha⁻¹) and high (200 kg ha⁻¹) superphosphate application. The most prevalent naturalised annual clover species Trifolium striatum, T. dubium, and T. glomeratum showed greater mean seedling recruitment in response to low superphosphate application with 996, 978, and 227 seedlings m⁻² respectively compared to high superphosphate application with 635, 466, and 123 seedlings m⁻² respectively (P<0.001), suggesting an affinity for lower sulphur and phosphorus fertility by these naturalised species.