Phosphorus response and efficiency of four adventive annual clovers grown in a New Zealand high country soil under glasshouse conditions

Maintaining and increasing legume abundance is a critical component of pastoral intensification, increasing nitrogen inputs to nitrogen deficient New Zealand high and hill country pastures and improving feed quality. Establishment and persistence of traditionally sown legume species white clover (Trifolium repens) and subterranean clover (T. subterraneum) is often limited in summer-dry high country. In contrast, naturalized, adventive annual pasture legume species such as cluster clover (T. glomeratum), haresfoot clover (T. arvense), striated clover (T. striatum) and suckling clover (T. dubium) persist on low fertility, summer-dry high and hill country slopes, although little is known about the edaphic requirements of these species. A glasshouse study was conducted to determine the response and efficiency of these four pasture legume species to increasing levels of available phosphorus (P) in a typical, low fertility, acidic New Zealand high country soil, comparing against white clover and subterranean clover as ‘reference’ species. Trifolium subterraneum was the most productive species (4.4 g dry matter [DM]/pot) and T. striatum yielded the least (0.8 g DM/pot). The order of greatest yield DM response was T. subterraneum > T. arvense > T. repens > T. dubium ≥ T. glomeratum > T. striatum, while the P application rates at which maximum yield occurred varied between species. Mean shoot P uptake was highest for T. subterraneum and lowest for T. striatum (24.1 and 3.8 mg P/pot, respectively). P-response efficiency by species was in the order of T. subterraneum > T. arvense > T. glomeratum > T. repens > T. dubium > T. striatum. Implications for low input, extensive grazing systems in high and hill country are discussed. Trifolium arvense and T. glomeratum show potential for further P response investigation under field conditions