Denitrification losses from outdoor piglet production: spatial and temporal variability

Animal welfare considerations have stimulated the development of outdoor piglet (Sus scrofa) production systems, but the high levels of nutrients excreted suggest that nutrient losses from this system may be high. This study first described the spatial distribution of denitrification activity in a 5- x 5-m grid within and outside a paddock immediately after the sows (32 sows ha(-1) for 6 mo) were removed in October 1997, and again the following March. Denitrification rates averaged 0.01 kg N ha(-1) d(-1) outside, and 0.5 kg N ha(-1) d(-1) inside the paddock in October, while the corresponding figures in March were 0.01 and 0.1 kg N ha(-1) d(-1). The highest denitrification rates were observed around the feeder, and this was also the case for concentrations of dissolved organic C and inorganic N in the soil. A statistical model that included both soil parameters and distance to feeder and huts gave the best description of the variability, but there was no significant autocorrelation between sampling points. In a second phase, seasonal variation of denitrification activity within a paddock (12 sows ha(-1) yr(-1)) was quantified; 10 soil cores were sampled along a transect 11 times between March 1998 and February 1999. There was a significant positive effect of dissolved organic carbon (DOC) on denitrification at <25% gravimetric soil moisture (i.e., to November in this study). Both climate and management (position of huts and feeder) appeared to influence denitrification, which was estimated to be 69 kg N ha(-1) yr(-1), or 11% of the N surplus of this production system.