Estoque de carbono e qualidade da matéria orgânica do solo em diferentes sistemas agropecuários em Belterra, Amazônia Oriental

Abstract

The aim of this work was to investigate the carbon stock and soil organic matter (MOS) quality after the conversion from forest-pasture and forest-soybean in Belterra-PA. The climate there is hot and humid, and the annual average temperature is 25.3 °C, while rainfall averages are 1943 mm, concentrated between January and June. The soil of the region is classified as very clayey yellow Latosol. In this research we investigated: (i) a soybean areas in minimum tillage with similar managements-18 years old; (ii) a soybean areas in minimum tillage with similar managements-8 years old; (iii) a nominal pasture (implanted four years ago, managed with fire, without soil fertility correction and managed with extensive livestock) and an improved pasture (implanted six years ago, managed with crop rotation and soil fertility correction by a period of three years. Subsequently, it only remained homogeneous pasture, where the beef cattle herd is managed in a rotational system); (iv) an area of dense ombrophylous forest, used as the reference. Soil samples were collected at six different equidistant points every 50 m. Deformed samples were collected from 0-10, 10-20, 20-30, 30-50, 50-80, 80-100 cm depths and undisturbed samples were collect until 50 cm depth. We estimated the carbon content, soil density, carbon stocks and the C:N ratio. Natural abundance of 13C:12C was used to estimate the amount of carbon from grasses incorporated into the soil. The quality of the MOS was evaluated by humification index and by its physical fractionation. The same soil layers from different areas were compared by analysis of variance and Tukey test (5%). Both pastures were compared between them and in relation to forest area and soybean crops were also compared between them and the forest area. Soil bulk density increased significantly after forest to pasture conversion and forest to soybean conversion. The carbon stock accumulated in the 0-50 cm layer and the degree of humification of the MOS did not differ between the areas. This similarity may be the result of the high clay content presented in this soil, which leads to organic matter slow decomposition, even after changes in vegetation cover. On the soybean areas, the carbon management index was lower in the longer cultivated area, indicating a loss of carbon in this soil. On pasture areas, improved pasture incorporated more carbon from C4 plants in the soil in relation to the nominal pasture, reflecting a positive effect of the rational management on this production system.

Ciclo do carbono e sistemas agroflorestais na sustentabilidade da produção agrícolas: revisão de literatura

“…Através dos resultados, concluiu-se que a maior quantidade de C armazenada no SAF se encontra na biomassa epígea, quando comparado a sistemas tradicionais de uso da terra e áreas nativas de cerrado, enquanto o solo superficial desse SAF não apresentou maiores quantidades de C quando comparados a sistemas tradicionais de uso da terra, assim como de áreas de cerrado nativo. Muchavisoy (2013), objetivando quantificar e comparar os estoques de C em diferentes usos do solo na Amazônia Oriental, estimou o C total (biomassa viva e morta acima do solo e C do solo) em formações vegetais de floresta ombrófila densa, floresta de restinga, sistemas agroflorestais multiestratificados complexos, comerciais, quintais, capoeiras e pastagens.…”