Phosphorus-efficient legume pasture systems - AWI Project #WP 564

Summary

​Phosphorus (P) fertiliser is a critical input for productive pasture systems in southern Australia but the cost of fertiliser has risen substantially.  There is a major opportunity to counter rising costs by improving the efficiency of P-use on farms.  

This project determined the critical soil test P requirements (i.e. soil test levels needed for near-maximum growth) of alternative pasture legumes to establish soil fertility benchmarks for pasture management.  Two species of serradella (Ornithopus sativa, O. compressus) were found to have very low critical P requirements relative to subterranean clover (Trifolium subterraneum) and it was estimated that their use in fertilised pastures could reduce P fertiliser costs by ~30% annually. 

When grown in moderately P-deficient soils the serradellas also achieved about twice the yield of subterranean clover.  Low-P pasture systems can be developed immediately in areas where serradellas are already grown.  Wider adoption hinges on understanding how widely serradellas can be grown in permanent pasture areas.  High P efficiency was associated with long, fine roots that have long root hairs.  This allows a plant to forage effectively for nutrients in soil. 

This knowledge is being used to identify more P-efficient lines of subterranean clover to improve yields in moderately fertilised paddocks and to push subterranean clover closer to the very high P efficiency of the serradella species.