Dr Jonathan McLachlan1, Dr Richard Flavel1, A/Prof Christopher Guppy1
1University Of New England, Armidale, Australia
Biography:
Dr Jonathan McLachlan is a Lecturer in Pasture Science and Grazing Management at the University of New England. Jonathan’s research focuses on optimising the feedbase of temperate and tropical grazing systems. He has a particular interest in legume establishment and persistence, by understanding the agronomy and nutrition of mixed pasture swards.
Abstract:
Tropical pasture legumes are expected to improve pasture productivity and forage quality in the extensive grazing systems of northern Australia. However, highly productive C4 grasses often outcompete these legumes, particularly if they are established in nutrient-deficient soils. A controlled-environment experiment was conducted to investigate the value of starter fertiliser for tropical legume growth across a range of soil P supplies. A low-P soil was amended with basal nutrients and six rates of P fertiliser (0–80 mg P kg–1, as KH2PO4 in the basal solution). The amended soils were then incubated for five weeks to prepare contrasting ‘native’ P treatments. Following incubation, micro-swards of Centro and Desmanthus were established in the six native P treatments, with or without an application of starter fertiliser (6 kg P ha–1 equivalent, as KH2PO4 solution). The seed and fertiliser were applied together in a shallow row. The shoot yield and tissue P concentrations of both legumes increased in response to native soil P supply. The application of starter fertiliser generally increased shoot yields and reduced the critical external P requirements of both legumes (by 38% for Centro and 74% for Desmanthus). It is likely that the localised application of P fertiliser enabled the legumes to develop more root length so that the soil volume could be exploited earlier. This would benefit early legume growth and establishment. These results suggest that starter fertiliser applications are likely to be appropriate for tropical pasture legumes, even in soil that has a moderate level of native P.