Stocking density determines nitrogen distribution in a farming production that combines free-range pigs and energy crops

Free-range pig farming is typically associated with a high risk of nitrogen leaching as the pigs’ excrement help create nitrogen’s hotspots. In addition, the pigs’ rooting behaviors destroy the grass-covered soil. The following study, which was published in the journal Agroforestry Systems, aimed to determine the role of stocking density in determining nitrogen distribution and balance in a farming production that combines free-range pigs and energy crops.

• The researchers hypothesize that combined production of free-range pigs and perennial energy crops such as silvergrass (Miscanthus), willow (Salix) and poplar (Populus) may benefit the environment because these crops may likely persist despite pig rooting, take up nutrients and thereby minimize nitrogen (N) losses.
• For each of two seasons, 36 growing pigs with an initial mean live weight of 55 kg (spring) and 48 kg (autumn) respectively were separated into six paddocks of two stocking densities (117 and 367 m² pig^-1), respectively.
• The team then measured soil mineral N in 0-25 and 25-75 cm depth at three occasions and found that N inputs exceeded N outputs at 626 and 185 kg N ha^-1 for high and low stocking density.
• The findings revealed that the pigs caused an uneven distribution of mineral N across the paddocks, with the highest content in zones with willow and poplar. They observed that stocking density significantly affects the content of soil mineral N.
• Immediately after the second batch of pigs, average mineral N in the 0-75 cm soil layer was on average 227 and 83 kg N ha^-1 at high and low stocking density, respectively.
• During winter period with no pigs, mineral N content in the 0-75 cm soil layer was reduced by almost 100 kg N ha^-1 in paddocks with high stocking density against only 4 kg in paddocks with low stocking density.

The researchers conclude that there was a low risk of elevated nitrogen leaching in the low stocking density, which means combining free-range pigs and energy crops in farming production may be a promising way to reduce the loss of soil mineral nitrogen.

Journal Reference:

Jørgensen U, Thuesen J, Eriksen J, Horsted K, Hermansen JE, Kristensen K, Kongsted AG. NITROGEN DISTRIBUTION AS AFFECTED BY STOCKING DENSITY IN A COMBINED PRODUCTION SYSTEM OF ENERGY CROPS AND FREE-RANGE PIGS. Agroforestry Systems. 2018 Jan 25. DOI: 10.1007/s10457-018-0200-3