Phosphorus management and requirements of tropical legume pasture swards

Tropical pasture legumes often lack persistence in the extensive grazing systems of northern Australia. However, their inclusion in these systems is expected to improve productivity through atmospheric nitrogen (N) fixation and increased pasture quality. Because the soils of northern Australia are often low in available phosphorus (P), it is expected that a greater understanding of legume P requirements and fertiliser application strategies will lead to better legume productivity and persistence. Numerous controlled-environment growth experiments were conducted to examine the P requirements of a range of tropical grasses and legumes. Subsequent experimentation focused on understanding the mechanisms behind P acquisition and identifying appropriate fertiliser application strategies for better legume growth. The results demonstrated that there are significant differences in yield potential and critical P requirements among tropical pasture species (including between grasses and legumes, and between different legume species). This indicates there is potential to select and use P-efficient species in soil that has inherently low P levels. The results also demonstrated that banded applications of P fertiliser can improve legume productivity in mixed pasture swards. These results have direct implications for the management of legumes and soil fertility in the extensive grazing systems of northern Australia.