PHOSPHORUS AND BEEF-PRODUCTION IN NORTHERN AUSTRALIA - .1. PHOSPHORUS AND PASTURE PRODUCTIVITY - A REVIEW

Phosphorus is a major limiting factor to pasture production in the tropics. Sown legume based pastures respond to added P fertilizer, responses varying with the initial soil P status, the species used and the rainfall. Native pastures are generally unresponsive to P since N is normally the major limiting factor. Differences between legume and grass species in their ability to utilize P have been exploited to reduce the need for expensive inputs of fertilizer P. The genus Stylosanthes is outstanding in its ability to grow well under conditions of low soil P. The perennial stylos have proven to be more stable under grazing than the annual stylos and are more efficient in utilizing P for growth. However, the P concentration of the forage may be too low for good animal production. Fertilization with P in conjunction with grazing management can dramatically alter botanical composition of the pasture. With stylo/grass pastures, grasses tend to dominate at high soil P, whereas at low P and increased grazing pressure stylo dominates. The combination of persistent legumes and the use of superphosphate fertilizer has been the key to improved pasture development. However, the high cost of superphosphate is now focusing attention on P efficient legumes, lower rates of fertilizer use and direct P supplementation of cattle.