Simulation of changes in C and N stocks with land use and cover in Amazon Forest-Cerrado transition environment

Abstract

Pastures store approximately 30% of the global terrestrial carbon (C) and are vital for the provision of several ecosystem services such as forage and climate regulation. In Brazil, sustainable management systems are being proposed to minimize environmental damage by carbon dioxide (CO2) emissions and increase soil C and nitrogen (N) stocks under pasture. Simulation models are important tools in the long-term assessment of C and N stock changes in pastures under different management practices. In this study, the Century model, version 4.0, was employed to simulate C and N stocks (0–20 cm layer) as well as forage biomass production in areas of pastures with different ages and different management practices. Carbon and N stocks simulated in the soil organic matter (SOM) equilibrium state under native vegetation were used in the adjustment of the deforestation model and subsequent establishment of pasture. Eight production scenarios for 2050 were simulated in comparison to the current situation depicted by absence of management practices (M), namely: pasture managed without periodic renewal (M1); pasture with chemical control of spontaneous plants (M2); pasture with only initial fertilization (M3); pasture with initial and maintenance fertilization (M4); pasture with initial and maintenance fertilization associated with chemical control of spontaneous plants (M5); silvopastoral system with 30% tree cover (M6); pasture managed with fire (M7); and pasture under intensive management (M8). Simulated scenarios revealed significant increases in C and N stocks, besides similar biomass production. Chemical control of spontaneous plants, initial fertilization at the time of pasture planting, and silvopastoral systems proved to be alternatives to maximize C sequestration. Simulated values of C stocks are strongly related to clay contents (SS2-18.2 t ha−1, SS3-60.0 t ha−1 and SS4-29.7 t ha−1). Similarly, N stocks also were higher in these areas (SS2-1.7 t ha−1, SS3-1.8 t ha−1 and SS4-2.1 t ha−1). Additionally, considering different scenarios, forage biomass production is conditioned by adopting management practices, such as control of spontaneous plants and initial fertilization. These results can assist national initiatives associated with management strategies which enhance pasture sustainability in Brazil. Modelling allows supply of information for the gap of data and appoint necessities of studies, especially for the Amazon region where Cerrado-forest transition areas are under strong pressure for agricultural occupation.