N-fertiliser application or legume integration enhances N cycling in tropical pastures

Abstract

Understanding the effects of N application or the introduction of a legume on N cycling is critical for achieving productive and sustainable grassland systems. This 2-year study assessed the N cycling of three pasture treatments: (1) mixed Marandu palisadegrass (Brachiaria brizantha) and forage peanut (Arachis pintoi) without N fertiliser (GRASS + LEGUME); (2) monoculture Marandu palisadegrass fertilised with 150 kg N ha⁻¹ year⁻¹ (GRASS + N); and (3) monoculture Marandu palisadegrass without N fertiliser (GRASS). Continuous stocking was used with a target canopy height of 0.20 to 0.25 m. Litter responses, forage and N intake, N livestock excretion and N cycling were measured. Existing litter and litter deposition rate were greatest in GRASS pasture (3030 and 84.3 vs. 2140 kg ha⁻¹ and 64.8 kg OM ha⁻¹ d⁻¹; average of GRASS + N and GRASS + LEGUME pastures, respectively; P < 0.10). Litter decomposition rate in GRASS pasture was smaller 30.4 and 36.0% compared to GRASS + N and GRASS + LEGUME pastures, respectively (P < 0.10). The GRASS + N obtained greatest (P < 0.10) faecal N excretion (21.7 vs. 13.8 kg N ha⁻¹ season⁻¹), and urinary N excretion (32.0 vs. 14.2 kg N ha⁻¹ season⁻¹). In the GRASS + N and GRASS + LEGUME pastures, there was a positive overall change of N in the soil–plant–animal system of 13 and 33 kg N ha⁻¹ year⁻¹, respectively. In the GRASS pasture, there was an overall negative change of N in the soil–plant–animal system of − 41 kg N ha⁻¹ year⁻¹. Nitrogen application or the integration of forage peanut in a grass pasture increased the conservation of soil N reserves.