Environmental impact of outdoor pig production: soil P forms evolution spatial distribution and P losses in drainage waters

when compared with intensive indoor production, outdoor pig production is considered by consumers as the production system that causes the least negative environmental effects and contributes to animal welfare. nevertheless, the continuous input of nutrients in food or pig excretions, increases soil nutrients levels, as is the case with phosphorus (p). this continuous soil p input may exceed soil retention capacity for phosphate and could lead to loss/transfer of p from soil to drainage or runoff waters, contributing to non point source pollution of superficial waters. the main objective of this work was to evaluate the impact of outdoor pig production on soil p levels, its spatial and temporal distribution and also p loss from this area to drainage waters. experimental outdoor pig production area has 2.8 ha, slope between 5 and 30%, with an animal charge of 9 adults/ha. an increase in soil p, evaluated by the olsen procedure (p-ol), and in p inorganic (pi) and organic (po) can be observed. in winter there are important p losses by rainfall but it was observed also a global increase in soil p levels with time. p lost in drainage waters is correlated with soil p-olsen or pi. levels of soil p-olsen above 20 mg kg-1 exceed soil p adsorbing capacity causing a significant increase in p transfer to drainage waters. better management practices and a better choice of an area with less erosion risk are important, in order to prevent eutrophication of water bodies.