Dr Jonathan McLachlan1, Dr Sajanee Gunadasa1, 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 species are often grown in a range of soils that are below their critical phosphorus (P) requirements. However, little is known about how key soil traits such as pH and PBI influence the critical P requirements of these species. Two controlled-environment experiments were conducted to investigate the effect of pH and PBI on the shoot yield and P acquisition of Digit and Desmanthus. In the first experiment, the two species were grown in low-P soil that was amended to achieve five soil pH treatments (4, 5, 6, 7 and 8). In the second experiment, the two species were grown in a low-P soil mix that contained varying combinations of a low PBI soil and a high PBI soil to achieve five soil PBI treatments (65, 145, 225, 305 and 385). Ten soil P treatments (0–120 mg P kg–1) were then prepared by adding KH2PO4 solutions to the soil surface. The shoot yields of Digit and Desmanthus increased in response to the higher application rates of P in both experiments. In the soil pH experiment, both species were most productive in the pH 5–8 treatments. Critical external P requirements were lowest in the pH 7 treatment and increased at lower and higher pH levels. In the soil PBI experiment, critical external P requirements increased significantly with PBI. Nevertheless, critical internal P requirements remained relatively constant. Tissue P tests may therefore be a useful way to determine likely responses of tropical pasture species to P fertiliser application across a range of soil types.