Estoques de carbono, nitrogênio e emissões de gases de efeito estufa sob diferentes condições ambientais em sistemas agropecuários na Amazônia Oriental.

Abstract

Land use changes in the Amazon can affect soil carbon (C) and nitrogen (N) stocks and intensify greenhouse gas (GHG) emissions. This study aimed to evaluate the effects of land use on C and N stocks and C origin, as well as the effects of land use, nitrogen fertilization, and temperature on carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in soils from the Eastern Amazon. The study was conducted in three municipalities in the state of Pará with different Köppen climates classifications: São Miguel do Guamá (Af), Capanema (Am), and Paragominas (Aw). Soil C and N stocks and C origin were evaluated in Af and Aw climates, while GHG emissions were quantified in incubation experiments using soils from the Am climate (land use effect) and Af climate (land use, fertilization, and temperature effects), under four land use types: forest, agriculture, intensive pasture, and nominal pasture. In the Af climate, soil C stocks ranged from 27.6 to 42.4 Mg ha−1 (0–30 cm) and from 59.4 to 75.5 Mg ha−1 (0–100cm), with no differences (p > 0.05) among land uses. For N, significantly higher stocks (p< 0.05) were observed under intensive pasture (3.2 Mg ha−1 at 30 cm and 5.3 Mg ha−1 at 100 cm). In the Aw climate, C stocks ranged from 63.9 to 77.4 Mg ha−1 (0–30cm) and from 117.1 to 134.5 Mg ha−1 (0–100cm), while N stocks ranged from 5.2 to 5.8 Mg ha−1 (0–30cm) and from 9.8 to 10.8 Mg ha−1 (0–100cm), with no differences (p > 0.05) among land uses. The δ13C isotopic analysis indicated substitution of forest-derived C by C4-C up to 60 cm in Af and up to 20cm in Aw, reflecting greater incorporation in wetter soils. In the Am climate, the highest cumulative CO2 emissions (246.0mg g−1) were recorded in the nominal pasture, while the highest N2O flux (64.3ng g−1) occurred in the intensive pasture. For CH4, all land uses acted as sinks, with greater oxidation observed in pastures (–199.7 to –249.3ng g−1) and lower oxidation in forests (–49.0 ng g−1). In Af, the highest CO2 (248.6mg g−1), N2O (175.4ng g−1), and CH4 (237.0 ng g−1) fluxes were also observed in soils under intensive pasture. Application of 180kg N ha−1 increased CO2 and N2O emissions, while CH4 showed a quadratic response, decreasing at higher doses. Temperatures of 30–35°C intensified GHG fluxes, while 45°C reduced all emissions. It is concluded that soil C and N stocks vary according to soil type, climate, and land use, and that intensive use increases GHG fluxes, with effects amplified by fertilization and temperature. Sustainable strategies, tailored to climate and soil conditions, are essential to mitigate environmental impacts on the biogeochemical functioning of Amazonian soils.