New insights into the role of agroforestry for controlling nitrate leaching from farrowing sow paddocks

Summary

Agroforestry brings benefits to outdoor animal husbandry but knowledge on its role in reducing nitrogen (N) surplus remains elusive. A field experiment was conducted on a commercial farm in Denmark with lactating sows and their piglets housed in 4 paddocks with grass-clover ley flanking a central poplar zone either managed (TM; cut down with biomass as coarse-sized wood chips used for surface mulching in the tree area) or unmanaged (TU), each with resources (feed and hut) on same (RS) or opposite side (RO). Spatial variation of soil water N in each paddock was depicted by suction cups at 1 m depth. Nitrate leaching estimated with support of a model varied seasonally and spatially from 7 to 860 kg N ha⁻¹ year⁻¹. Although RO changed soil N distribution, no clear leaching effect occurred. Lower leaching in the tree zone of intact trees indicated that cutting poplar reduces N-uptake. On average, nitrate leaching in the experimental year was in the order TM-RO > TM-RS > TU-RO > TM-RS, i.e., 231a > 214ab > 170b > 163b kg N ha⁻¹ across zones. These results highlight the role of trees and resource position for distributing nitrate leaching in outdoor pig systems.