The effects of cover crops and organic amendments on phosphorus cycling in agricultural soils of California

Phosphorus (P) is a major limiting nutrient in agriculture because only a small fraction of soil P is typically available to plants. Mineral fertilizers are commonly used to increase P availability and yields, but low P recovery in crops, increasing costs, and eutrophication concerns highlight the need for alternative P fertilization strategies. Among these, using organic amendments (composts, manures) allows to recycle P more efficiently within farming systems but often results in P over-fertilization, whereas cover crops may help to convert soil P into plant-available forms and reduce soil P losses, but their effect might be too small to be of agronomic significance. I will present results from two long-term field experiments, two greenhouse experiments (including the use of 33P tracers), and farm-gate budgets to determine how cover crops and organic amendments affect soil P cycling and P budgets in California farming systems.