Legume integration or N fertilisation enhances the N cycling in the soil-plant-animal system

Grassland degradation is exacerbated due to lack of grazing management practices and limited cycling of N. Nitrogen input via fertiliser or biological fixation is critical for achieving productive and sustainable grassland systems. This two-year study assessed the N cycling of three pasture types (PTs): (1) mixed Marandu palisadegrass (C4; Urochloa brizantha) and perennial horse gram (C3; Macrotyloma axillare) without N fertiliser (Mixed); (2) monoculture Marandu palisadegrass fertilised with 138 kg N ha⁻¹ yr⁻¹ (N-fertilised); and (3) monoculture Marandu palisadegrass without N fertiliser (Unfertilised). Litter responses, forage, and N intake, N livestock excretion and N cycling were evaluated. There were no differences between treatments for the existing litter (an average of 3,485 kg ha⁻¹; P = 0.204). More N was cycled via litter in the Mixed pasture than in the N-fertilised and Unfertilised pastures (95.7 vs. 63.6 and 51.8 kg N ha⁻¹ season⁻¹; P < 0.001). There was no difference between PTs for the total N excretion per animal (an average of 79.5 g animal d⁻¹; P = 0.727). However, the higher stocking rate on the N-fertilized pasture increased total N excretion per hectare by 20.4 and 22.5% compared to Mixed and Unfertilized pastures, respectively (P = 0.010). In the N-fertilised and Mixed pastures, there was a positive overall change of N in the soil–plant-animal system of 83.5 and 28 kg N ha⁻¹ year⁻¹, respectively. In the Unfertilised pasture, there was an overall negative change of N in the soil–plant-animal system of −27 kg N ha⁻¹ year⁻¹. Nitrogen application or perennial horse gram integration in a grass pasture increased the N cycling in the soil–plant-animal system.