Nitrogen losses from outdoor pig farming systems

Nitrogen losses via nitrate leaching, ammonia volatilization and nitrous ox ide emissions were measured from contrasting outdoor pig farming systems in a two year field study Four 1-ha paddocks representing three outdoor pig m anagement systems and an arable control were established on a sandy loam so il in Berkshire, UK. The pig management systems represented: (i) current co mmercial practice (CCP) - 25 dry sows ha(-1) on arable stubble; (ii) 'impro ved' management practice (IMP) - 18 dry sows ha(-1) on stubble undersown wi th grass, and (iii) 'best' management practice (BMP) 12 dry sows ha(-1) on established grass. Nitrogen (N) inputs in the feed were measured and N offt akes in the pig meat estimated to calculate a nitrogen balance for each sys tem. In the first winter, mean nitrate-N concentrations in drainage water f rom the CCP, IMP, BMP and arable paddocks mere 28, 25, 8 and 10 mg NO3 l(-1 ), respectively. On the BMP system, leaching losses were limited by the gra ss cover, but this was destroyed by the pigs before the start of the second drainage season. In the second winter, mean concentrations increased to 11 1, 106 and 105 mg NO3-N l(-1) from the CCP, IMP and BMP systems, respective ly compared to only 32 mg NO3-N l(-1) on the arable paddock. Ammonia (NH3) volatilization measurements indicated that losses from outdoor dry sows wer e in the region of 11g NH3-N sow(-1) day(-1). Urine patches were identified as the major source of nitrous oxide (N2O) emissions, with N2O-N losses es timated at less than 1% of the total N excreted. The nitrogen balance calcu lations indicated that N inputs to all the outdoor pig systems greatly exce eded N offtakes plus N losses, with estimated N surpluses on the CCP, IMP a nd BMP systems after 2 years of stocking at 576, 398 and 264 kg N ha(-1), r espectively, compared with 27 kg N ha(-1) on the arable control. These larg e surpluses are likely to exacerbate nitrate leaching losses in following s easons and make a contribution to the N requirement of future crops.