Grazing intensity and seasonality regulate N cycling via litter and excreta in tropical grass–legume pastures

Abstract Integrating forage legumes into grasslands reduces the need for N fertilization, but its effectiveness depends on grazing management. This 2 years study evaluated N cycling in Urochloa brizantha and Arachis pintoi pasture under severe (10 cm stubble height), moderate (15 cm stubble height), and light (20 cm stubble height) grazing intensities. Nitrogen cycling from litter and livestock excreta were assessed. Moderate grazing decreased in 243 kg ha⁻ 1 existing litter, but increased legume proportion in the litter (13.4%) compared to severe (7.8%). Pre-grazing legume mass was lower under moderate grazing than under light grazing by 785 kg ha⁻ 1 , and post-grazing legume mass under light grazing was 57% greater than the mean value observed under moderate and severe grazing. Moderate grazing led to a lower litter deposition rate but reduced C/N ratios in both existing and deposited litter compared to light grazing. Nitrogen intake was 73% greater in the rainy season than in the dry season. Furthermore, severe grazing increased N intake and excretion by 47.7 kg ha⁻ 1 season⁻ 1 due to the higher stocking rate associated with this treatment. Nitrogen cycled from litter was greatest under light grazing during the dry season but peaked under severe grazing in the rainy season (+ 41 kg ha⁻ 1 season⁻ 1 ). Mixed pastures should be managed with a pre-grazing height of 24–30 cm and a stubble height of approximately 15 cm to improve N cycled via litter with lower C:N ratio and greater fecal over urinary N excretion, potentially reducing N losses and improving nutrient recycling efficiency.