Investigation of the soil properties that affect Olsen P critical values in different soil types and impact on P fertiliser recommendations

Summary

This pot experiment examined how soil properties influence the critical Olsen P values used to guide phosphorus fertiliser recommendations across 10 contrasting soils. Although phosphorus availability was clearly affected by soil pH and metal (hydr)oxide contents, the critical Olsen P values for optimum ryegrass yield varied between soils in ways that could not be explained by measured soil properties, suggesting that current blanket fertiliser recommendations based on Olsen P are inappropriate and soil-specific guidance is needed.

UK applicability

Given the UK-based authorship and likely UK study soils, these findings directly inform phosphorus fertiliser advice for UK farmers. The results suggest that current blanket Olsen P critical values may lead to suboptimal or excessive fertiliser use in UK soils, with implications for both farm economics and water quality management.

Key measures

Olsen P values, added phosphorus fertiliser rates, ryegrass yield response, soil pH, manganese oxide content, crystalline aluminium oxide content, amorphous iron oxide content

Outcomes reported

The study investigated how soil properties affect critical Olsen P values and phosphorus fertiliser availability across 10 different low-P soils using ryegrass yield response in a pot experiment. Results showed that the relationship between added phosphorus and Olsen P values varies substantially between soils and is influenced by pH, manganese oxide, crystalline aluminium oxide, and amorphous iron oxide contents.

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