Avaliação da degradação, composição química e dinâmica temporal de gramíneas em pastagem de várzea no município de Parintins-AM

Abstract

Cattle ranching in Amazonian floodplain ecosystems relies heavily on climate seasonality and the resilience of native pastures. This study aimed to evaluate the degradation degree, chemical composition, and botanical composition of a native floodplain pasture in the municipality of Parintins-AM, across two evaluation cycles influenced by the El Niño (2023) and La Niña (2024) phenomena. The experimental design evaluated forage biomass, canopy height, and soil cover across four sampling periods per cycle. Chemical analyses integrated the levels of dry matter (DM), crude protein (CP), and neutral detergent fiber (NDF). Botanical identification confirmed the continuous dominance of Cynodon dactylon and the seasonal presence of Paspalum repens, regulated by the river flooding pulse. Results indicated that forage cover fluctuated between 50% and 75%. The year 2023 exhibited a severe drop in biomass due to the extreme drought, whereas 2024 showed a linear recovery in dry matter production (from 132,9 to 868,5 kg/ha between months 1 and 2) driven by late rainfall accumulation. Chemical composition revealed critically high NDF levels, exceeding 70% in both years, which limits digestibility. However, CP levels demonstrated good protein potential, oscillating between 8.55% and 17.77%, with peaks associated with leaf regrowth post-water stress. In conclusion, the productive and qualitative dynamics of native pastures are strictly regulated by interannual climate fluctuations and the regional hydrological regime. Therefore, local livestock management must adjust the carrying capacity to this seasonality to optimize animal performance and mitigate degradation risks in the floodplain ecosystem.