Phosphorus (P) in animal manures represents approximately 17 Tg P year-1, which is slightly more than the amount of P contained in mineral fertilizers used worldwide (14 Tg P year-1). Manures are generally spread on agricultural soils, so that it can be considered that P (and other elements) contained in these materials are recycled. However, there are several factors limiting an optimal recycling of this P resource. The aim of this communication is to discuss these barriers. Manures are effective sources of P to compensate P exports over a crop rotation, provided background soil test P is adequate. When soil P availability is critical, the short-term P availability of any organic material applied as a fertilizer becomes an issue. Questions remain about the short-term bioavailability of P supplied by organic products, depending on the overall composition of the biosolid (C/N/P ratio especially) and onP chemical forms. Because of this uncertainty, the amount of P supplied by organic products is often underestimated by farmers, and the need for additional mineral P fertilizers is overestimated. The N to P ratio of many organic products is lower than the N to P ratio characterizing crop requirements, so that a N based fertilization strategy results in an over-application of P and a low efficiency of manure P utilization. Last but not least, an optimal recycling of P and other nutrients contained in manures is increasingly constrained by the current trend towards specialization and geographical segregation of arable and livestock farms. The technical and organizational innovations that could overcome these barriers will be presented.< Leer menos