Paddock design influences soil inorganic nitrogen distribution in a pasture-based sow system with poplar trees

In pasture-based pig production, high soil inorganic nitrogen (N-inorg) amount and uneven distribution combined with low vegetation cover lead to nitrate leaching. Integrating trees can mitigate this by maintaining a vegetation ensuring nitrogen (N) uptake, but there is limited knowledge on how to implement this approach. An on-farm experiment was conducted using 16 single sow paddocks with grass-clover ley and centrally located poplar trees to investigate the effect of paddock design on elimination behaviour, area covered with faeces and herbaceous vegetation, and distribution of N-inorg. Four treatments were evaluated in three consecutive sow batches, involving 48 lactating sows, combining 1) tree management—cutting trees with application of wood chips as mulch under the trees or unmanaged trees; and 2) sow resource position—placing the hut and feeding trough on the same side or opposite sides of the trees. Topsoil N-inorg concentrations were sampled initially, after two, and after three sow batches. Elimination behaviour and area covered with faeces indicated higher N deposition within the tree zone compared to the grass zones, with no clear treatment effect. However, N-inorg was more evenly distributed in paddocks with resources on opposite sides of the trees by ranging at 41.9–44.2 kg N ha⁻ 1 instead of 23.8–76.1 kg N ha⁻ 1 . Higher N-inorg amount was associated with lower herbaceous vegetation cover. Tree management had no effect. These findings suggest that a paddock system with centrally placed poplar trees and huts/feeders on either side may enhance the distribution of soil N-inorg and potentially reduce N leaching.