Organic phosphorus fertilizers outperform mineral fertilization in a Mediterranean crop rotation

Phosphorus (P) scarcity is forcing a shift from mineral-based fertilization to a circular economy-based strategy. However, replacing P mineral fertilizer with organic fertilizers requires further research under field conditions, given the complexity of the P forms present in these fertilizers. To assess the efficiency of organic P fertilizers, a field study was conducted in southern Spain, comparing olive husk compost and two vermicomposts with superphosphate. The experiment was replicated twice between 2018 and 2022, involving each one a 3-year crop rotation (durum wheat-sunflower-pea), where fertilization was only applied before the first crop. The apparent P recovery (APR) in the first crop was not significantly different between the fertilizers. However, in the entire rotation, APR was significantly higher with all organic fertilizers than with superphosphate, reaching values of 18–30 %, and without differences in Olsen P. Overall, organic fertilizers tended to increase the harvest index, the P harvest index, and the P use efficiency when compared with superphosphate. The moderately labile mineral P in the organic fertilizers (20–72 % of total P) cannot explain their increased efficiency, which was attributed to less precipitation of insoluble phosphates due to the progressive mineralization of organic P and the effect of organic matter in the fertilizers. In some cases, greater soil phosphatase activity contributes to improved P supply to crops. The results reveal that organic fertilizers can effectively replace mineral fertilizers in rainfed Mediterranean crop rotations, with a significant residual effect when fertilization is not applied annually. • Organic fertilizers can substitute the use of mineral fertilizers. • Organic fertilizers increase the apparent P recovery relative to mineral fertilizers. • Outperformance of the organic fertilizer is highlighted in the full crop rotation.