Forage production and nitrogen dynamics in silvopastoral systems with Leucaena diversifolia in Urochloa grass-based pastures

In tropical regions, cattle production often relies on grass monocrops (GMC), which limit productivity and land-use efficiency. Sustainable intensification of pastures is needed to meet rising demand for animal-source foods. Silvopastoral systems (SPS) with nitrogen-fixing legume trees, such as Leucaena diversifolia, offer a potential solution but may increase nitrous oxide (N₂O) emissions due to higher nitrogen (N) inputs. We conducted a one-year study comparing Urochloa GMC versus SPS with L. diversifolia on a fertile Pachic Haplustoll in Valle del Cauca, Colombia. Two grass cultivars were evaluated: Urochloa hybrid cv. Cayman and U. brizantha cv. Toledo. In SPS, tree rows created two zones: grass-only (SPS/GO) and under-tree (SPS/UT). We measured forage biomass, grass N uptake, N₂ fixation by L. diversifolia, and soil N₂O emissions under two conditions: no additional N input (+water) and after urine deposition (+urine). SPS produced 30% more forage dry matter than GMC. Leucaena diversifolia obtained 54% of its N from atmospheric fixation. The grass in SPS absorbed 8 kg N ha⁻¹ more per grazing cycle than GMC. Under no additional N inputs, soil N₂O emissions were higher in SPS/UT, likely due to greater N recycling. With urine addition, emissions were variable, with higher values in SPS/GO, but no statistical difference was found between SPS/UT and GMC, possibly due to inappropriate urine-N overdosing in GMC. Although SPS showed higher N₂O emissions under specific conditions, their greater forage yield and quality, plus potential co-benefits like lower enteric methane emissions and higher carbon capture, indicate a favorable production-environment trade-off.