Nitrogen distribution and potential nitrate leaching in a combined ...

Abstract
There is a conflict between animal welfare and nitrogen pollution in free range pig
production. In response to the concern about nitrogen being lost to the environment and the
need of sources of renewable energy, a combined production system of free range pigs and
perennial energy crops was established. The pigs caused an uneven distribution of mineral
nitrogen in the soil verified by observations of defecation behavior and soil Nmin analyses. The
investigation was carried out from March 2009 to April 2010. Areas planted with energy
crops were favoured by the pigs for excretion of faces and urine. This created nitrogen hot
spots with risk of nitrogen leaching. Stocking density had a pronounced effect on nitrogen
losses per ha. After 16 weeks with a high stocking density (372 kgN/ha) rates of nitrogen
losses to the environment were estimated for nitrate leaching (30 kgN/ha), ammonia
volatilization (37 kgN/ha) and denitrification (63 kgN/ha). In comparison reduced stocking
density (116 kgN/ha) resulted in 69 % less nitrogen removed from the paddocks with the pigs,
when they were sent to the abattoir. However, reduced stocking had generally a smaller
influence on the environment from estimated nitrate leaching (4 kgN/ha), ammonia
volatilization (12 kgN/ha) and denitrification (20 kgN/ha). Additionally around 70 % less
nitrogen was left for accumulation in soil at the low stocking density. However, the
investigated energy crops were resistant to the rooting behavior of the pigs and were
estimated to have a crop nitrogen off-take, if harvested in summer, of 87 and 60 kgN/ha at
high and low stocking densities respectively. These values are probably underestimated and
further investigations are needed. Paddocks planted with energy crops are a better alternative
to open grassland with less persistent crops and higher potentials of nitrogen leaching.
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