Soil pH and phosphorus (P) fertiliser can interact to make soil phosphorus more available. This can happen when:
- there are no other major nutrient deficiencies.
- recent lime application has produced a large change in soil pH (>0.5 pH units).
The soil pH and P interaction is driven by changes to root growth in the subsoil rather than pH-induced changes to soil P. Soil pH in 10-20 cm appears to be an important factor. Shifting from below ~ pH 4.5 to above this level increases yield potential and uptake of soil P.
Field experiments across four sites in Western Australia have established this link between pH change and P fertiliser. A significant grain yield response to P fertiliser was observed even where soil P (Colwell P) in the 0-10 cm layer was above critical ranges.
Soil pH through the profile appears to be an important factor in the difference between predicted and observed grain yield responses to P fertiliser. At low soil pH the difference between predicted grain yield response to P fertiliser and the actual response is greater.