Spatial variability of soil phosphorus in grazing systems

Phosphorus (P) use efficiency has been identified as a key issue for Australian grazing systems. This project examined the spatial variability in soil P concentration from two separate surveys of grazed pasture fields. A field on the central tablelands of NSW had a range in Bray P of 1.2 to 140 mg/kg and a COV of 107%. The other field on the northern tablelands of NSW reported a range in Colwell P from 13.0 to 121.1 mg/kg and a COV of 59%. Maps of the spatial variability of soil P demonstrated that there is a relationship with field elevation. Application of critical P values to both fields enabled an estimation of the value of site specific fertiliser management. For one field, fertiliser inputs could potentially be isolated to 37% and the other 56% if nutrient additions were targeted at responsive areas. The opportunity for increased fertiliser use efficiency through site specific management (SSM) warrants further investigation. Research is required into both the value of SSM and the techniques that might enable the development of this strategy.