Critical Soil Phosphorus Values for Yield Reduction in Intensive Agricultural Systems

Abstract

Phosphorus (P) is an essential element for agricultural production. Over-fertilization during decades caused an accumulation of P in soils leading to eutrophication in regions characterized by intensive agriculture. These environmental concerns together with the non-renewability of P resources have led to a more sustainable P use. Knowledge about the P need of crops is essential for a sustainable agriculture thereby minimizing P losses to the environment without lowering the yield substantially. Therefore, in this study, critical soil P values for yield reduction (P Crit) were determined based on fertilizer trials conducted between 1970 and 1988 and more recent fertilizer trials (2016-2017). At rotational level a common P Crit value of 109 mg P/kg dry soil (in an ammonium lactate and acetate extract) was determined. Crop specific P Crit values were also determined for seven crops (potato, winter wheat, barley, rye, maize, sugar beet and temporary grassland). These critical values ranged from 59 mg P/kg dry soil to 164 mg P/kg dry soil with winter wheat the least and maize the most sensitive towards P deficiency. The diversity in P Crit values among crops can mainly be explained by the root intensity but also rooting depth, exudation of organic acids and phosphatases may influence the P Crit value. The soil pH also influenced the P availability significantly. Soils with a favorable pH had a significantly higher availability (i.e., lower P Crit value) for all crops compared to soils with a suboptimal pH. Critical soil P values might help to set up new or to evaluate current soil P in target zones used for P fertilizer recommendations.