Measuring phosphorus in soils when using natural phosphate fertilisers

The Olsen and Colwell soil tests are strongly correlated when using water soluble/chemical fertilisers. However, these tests will likely underestimate plant available phosphorus (P) when fertilising with RPR or BioAgPhos.

A key part to improving farm productivity is measuring soil P levels.

P is an important element for normal plant growth and is often limiting nutrient for plants. There could be different reasons in the agricultural practice, but mainly this is due to the challenges in the management of soil phosphorus.

Traditional Olsen and Colwell tests will typically underestimate plant available P when using a RPR based fertiliser. When transitioning to or having applied fertilisers containing RPR it is important to analyse soils using Bray 1, Bray 2 and PBI.

By assessing these three parameters along with the soil content of antagonists; iron, aluminium, calcium and beneficial soil components sulphur and organic carbon levels, assessments can be made on plant available P, and by performing year on year tests P accumulation or consumption can be monitored.