b'Effects of manure type and soil properties on phosphorusbioavailability and environmental riskHebert R1,2,3, Jordan P3, McDonald NT4, Vero S5, Mellander P-E1 , 2 and Wall DP21Agricultural Catchments Programme, Teagasc, Johnstown Castle Environmental Research Centre, Wexford, Co. Wexford, Ireland2Crops, Environment and Land Use Programme, Teagasc, Johnstown Castle EnvironmentResearch Centre, Wexford, Co. Wexford, Ireland3School of Geography and Environmental Sciences, Ulster University, Coleraine, Northern Ireland, United Kingdom4Department of Food, Agriculture and the Marine, Agriculture House, Dublin5Agri-Food and Bioscience Institute (AFBI), Newforge Lane, Belfast BT9 5PXThe application of phosphorus in organic manures can maintain soil fertility but a challenge is to avoid over application and risk of nutrient losses, potentially decreasing water quality.To evaluate the effects of soil properties, time after application and fertiliser/manure type on soil P pools, a soil microcosm incubation study was undertaken using four soil types, each at low and high initial soil P concentrations. Five treatments, chemical P, cattle slurry, pig slurry and hen manure, applied at a rate of 100 kg P ha-1, and a zero P control were investigated. The soils were sampled at three time points (0, 70 and 140 days) and analysed for Morgans P (P bioavailability), water extractable P (WEP - mobility) and P saturation ratio (PSR - buffering). All treatmentsequilibrated within 70 days but different soil P pool responses were shown between treatments and between initial soil P concentrations. Pig slurry and hen manure induced the greatestincreases in bioavailable P from all initial soil P concentrations providing good opportunity for immediate and longer term soil fertility. All manures also increased WEP following equilibrium but this was often significantly lower than chemical P, indicating lower longer term P loss risk,especially cattle and pig slurry. However, WEP increased significantly more for pig slurry andhen manure in the time before equilibrium and further work is required to determine the extent of environmental risk following application of these treatments. These findings should beconsidered in policy reviews that try to balance soil P fertility and crop requirements withenvironmental risk. These results can also underpin soil analysis and nutrient managementadvice for farmers to help decisions on the right manure choice, applied at the right rate,at the time in the right place. Keywords:soil test phosphorus; water extractable phosphorus; organic manures; soil type;Morgans P; environmental risk.4'