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 investigated which soil properties determine critical Olsen P values—the threshold at which phosphorus fertiliser applications achieve optimum ryegrass yield. The authors demonstrate that P availability from applied fertiliser is influenced by soil pH and metal (hydr)oxide composition, but that the critical Olsen P values for yield optimisation vary substantially between soils. The findings call for soil-specific rather than universal phosphorus fertiliser recommendations to improve fertiliser use efficiency and reduce eutrophication risk.

UK applicability

Given the UK authorship and focus on ryegrass in temperate soils, these findings are directly applicable to UK grassland management and fertiliser guidance. The research suggests that current uniform P fertiliser recommendations may be suboptimal for diverse UK soil types and could inform revision of soil testing protocols and advisory standards.

Key measures

Olsen P values, added P fertiliser rates, ryegrass dry matter yield, soil pH, manganese oxide, crystalline aluminium oxide, amorphous iron oxide contents

Outcomes reported

The study measured how soil properties affect the relationship between added phosphorus, resultant Olsen P values, and ryegrass yield response in ten low-available-P soils. It identified soil pH and metal (hydr)oxide contents as drivers of P availability, but found that critical Olsen P values varied widely between soils without clear correlation to measured soil properties.

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