This study investigated phosphorus (P) retention materials of sand and limestone outside houses in paddocks for organic laying hens, as a measure to retain P and reduce leaching. When manure P, accumulated in the materials during 6 months, was exposed to rain simulations in a lysimeter study, P concentrations in drainage water were high from all treatments (58-136 and 130-197 mg L-1 of PO4-P and total-P respectively). On average, 14% of the manure P, captured in the materials was leached after 100 mm of simulated rainfall. The conclusion is that these materials may efficiently retain P during the outdoor season (May to October), but in order to reduce the risk of losses to waters during the following winter they need to be removed from the paddocks, preferably to arable fields. The materials can be regarded as potential P fertilizers and may thereby combine increased P use efficiency and environmental performance of organic outdoor poultry systems
