Consórcios de gramínea e leguminosas em pastagens tropicais: respostas produtivas, desempenho animal e emissão de metano entérico

Abstract

Brazilian beef cattle production is predominantly based on pasture systems, whose productivity depends on forage availability and quality. However, pasture degradation and growing concerns regarding greenhouse gas (GHG) emissions have reinforced the need for strategies that improve both the productive and environmental efficiency of these systems. In this context, grass–legume intercropping has emerged as a promising strategy by promoting biological nitrogen fixation, improving forage nutritive value, and reducing the dependence on nitrogen fertilizers. This study aimed to determine the effects of including forage legumes in Urochloa brizantha cv. Marandu pastures on forage productivity, Nellore heifer performance, and greenhouse gas emissions. The experiment was conducted at the experimental area of the Department of Animal Science, Federal University of Lavras, Lavras, Minas Gerais, Brazil. Five pasture systems were evaluated: marandu grass monoculture without nitrogen fertilization (B), marandu grass fertilized with 150 kg N ha⁻¹ year⁻¹ (B+N), marandu grass intercropped with forage peanut (B+A), marandu grass intercropped with pigeon pea (B+G), and marandu grass intercropped with forage peanut and pigeon pea (B+A+G). Pastures were managed under intermittent stocking with a variable stocking rate using Nellore heifers. Forage mass, botanical composition, forage nutritive value, animal performance, and enteric methane emissions were evaluated. During the pre-grazing period, the greatest grass forage mass was observed in B+N, whereas the greatest herbaceous forage mass occurred in B+A, B+N, and B+A+G, and the greatest total forage mass was recorded in B+G. The highest crude protein concentrations of the grass were observed in B+A (12.6%), B+N (11.6%), and B+A+G (10.7%). The B+A treatment showed the highest stocking rate (1.9 AU ha⁻¹), indicating greater pasture carrying capacity, whereas the highest average daily gain (ADG) was observed in B+A+G and B+A during the rainy season (0.771 and 0.553 kg day⁻¹, respectively). Furthermore, B+A presented the lowest enteric methane emission intensity during the rainy season. Nitrogen input, either through forage legumes or nitrogen fertilization, improves forage quality and increases pasture carrying capacity, representing a sustainable alternative to the exclusive use of nitrogen fertilization in tropical pasture systems.