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

Summary

In pasture-based pig production, high soil inorganic nitrogen (N-inorg) content and uneven 16 distribution combined with low vegetation cover lead to nitrate leaching. Integrating trees in 17 the grazing area can mitigate this by maintaining a vegetation ensuring nitrogen (N) uptake, with little knowledge on how to obtain the optimal effect. An on-farm experiment was 19 conducted using 16 single sow paddocks with grass-clover ley and centrally located poplar 20 trees (Populus sp.) to investigate the effect of paddock design on elimination behaviour 21 (defaecations and urinations), faeces cover and herbaceous cover, and distribution of N-inorg. 22 Four treatments were evaluated in three consecutive sow batches, involving a total of 48 23 lactating sows, combining 1) tree management, either cutting trees with application of wood 24 chips as mulch under the trees or unmanaged trees; and 2) resource position, placing the hut 25 and feeding trough on the same side or on opposite sides of the trees. Topsoil N-inorg 26 concentrations were sampled initially, after two, and after three sow batches. Elimination 27 behaviour and faeces cover indicated higher N deposition within the tree zone compared to the 28 grass zones, with no clear effect from treatments. However, N-inorg was more evenly 29 distributed within the paddock with resource position on opposite sides of the trees by ranging 30 at 41.9–44.2 kg N ha⁻¹ instead of 23.8–76.1 kg N ha⁻¹. Higher N-inorg content was associated 31 with lower herbaceous vegetation cover. Tree management had no effect, indicating unchanged 32 poplar N demand and low N immobilisation by the large and non-incorporated wood chips.