Phosphorus response and optimum pH ranges of twelve pasture legumes grown in an acid upland New Zealand soil under glasshouse conditions

摘要

Pasture legumes provide critical nitrogen inputs but fail to persist in typical acidic low P fertility upland soils. Alternative legume species for these environments are urgently sought. Twelve novel legume species were grown for 42 weeks under glasshouse conditions in an acidic upland New Zealand soil. Phosphorus (P) was applied at eight rates (0, 10, 30, 60, 100, 250, 500, 1500 mg kg-1 soil) or lime (100% CaCO3) at five rates (0, 2, 5, 8, 15 t ha-1 equivalent). Annual species grew on average for 25 weeks, while perennial species grew for 42 weeks. Yield was measured and herbage was analysed for macro and micro elements and soils analysed for pH, exchangeable Al and Olsen P. P responses differed substantially between legume species which were likely driven by genetic adaptations to low phosphorus environments. Critical shoot P concentrations for optimum yield were identified and ranged from 0.23 (tagasaste) to 0.39 % P (falcata lucerne). Arrow leaf, subterranean and balansa clovers had the greatest yield increase at low P inputs (100 mg P kg-1) and show promise as alternatives to white clover. Lime treatments increased the yield of all species to a point beyond which yield decreased with further additions. Increased yield was primarily driven by decreased soil exchangeable aluminium (Al) concentrations and to a lesser extent by increased soil P and molybdenum (Mo) availability, while decreases were driven by lower soil P and boron (B) availability at high pH. Thresholds for soil exchangeable Al differed between legume species. Species with higher Al thresholds (7 - 8 mg Al kg-1) were tagasaste, lotus, persian and gland clovers and falcata lucerne. These species show promise for acid soil environments with soil Al issues and should now be investigated further in field experiments. For many of these legume species this represents new and critical information.