The influence of tropical pasture improvement on animal performance, nitrogen cycling, and greenhouse gas emissions in the Brazilian Atlantic Forest

Abstract

This study evaluated beef cattle performance, nitrogen (N) dynamics, and potential greenhouse gas emissions (GHG) in tropical pastures receiving N fertilization or mixed with legumes. During the cool season, 54 Nellore heifers were randomly allotted to continuous grazing in three plots of each pasture type: T1 (Marandu grass with 150 kg N/ha), T2 (Marandu grass with 120 kg N/ha), T3 (Marandu grass with Arachis pintoi), T4 (Marandu grass with Desmodium heterocarpo), T5 (Marandu grass without N fertilization), and T6 (degraded pasture). The stocking rate was periodically adjusted to achieve the target canopy height of 20–25 cm. Animal performance and N livestock excretion were estimated by variation in live weight and spot samples of urine and feces, respectively. GHG emissions were calculated using the methodology of the Intergovernmental Panel on Climate Change. Animal performance was higher in fertilized and mixed pastures (e.g., T1 to T4) than in T5 and T6 pastures. Heifers grazing on T1, T2, T3, and T4 excreted lower amounts of urine with higher N concentrations than heifers grazing on T5 and T6. Heifers grazing in T2 and T4 pastures had a lower concentration of fecal N than those grazing on other pastures, reflecting lower N excretion in this form. The potential for direct nitrous oxide emissions per unit area in pastures mixed with legumes was approximately four times lower than that in pastures with mineral N fertilization. The recovery of degraded pastures and the inclusion of forage legumes contributed to maintaining the sustainability of animal production in pastures