The fate of nitrogen in outdoor pig production

There may be a conflict between animal welfare and nitrogen pollution in outdoor pig production. In response to concern about nitrogen being lost to the atmosphere and ground water we quantified spatial variation and temporal dynamics of mineral N, ammonia volatilization, denitrification and nitrate leaching from outdoor pig production at three commercial farms in Denmark. From paddocks containing farrowing sows substantial nitrogen losses were observed, particularly around the feeding areas. Gross ammonia emission rates varied between 0.08 and 1.26 kg N.ha(-1).d(-1) and increased with animal density and N intake. The mean annual loss of ammonia per sow was 4.8 kg N. Denitrification rates averaged 0.52 kg N.ha(-1).d(-1) in autumn following summer grazing with lactating sows, and 0.10 kg N.ha(-1).d(-1) in the following spring. Denitrification losses up to 69 to 114 kg N.ha(-1) were estimated. Cumulated nitrate leaching during sow grazing and in the following year was 126-276 kg N.ha(-1). Of the N input in feed to the paddock 44% could be accounted for in piglets, 13% as ammonia volatilization, 8% as denitrification and 16 to 35% as nitrate leaching. The necessary development towards increasing N-use efficiency in outdoor pig production may include changes in management, such as lowering the stock density and reducing the level of dietary N. Also, a more uniform distribution of nutrients in the field may be achieved by manipulating the excretory behavior of the animals.