Intensificação do uso da terra com sistemas integrados de produção agropecuária: efeito das modalidades e dos arranjos na ciclagem de nutrientes e estoques de carbono do solo

Abstract

Diversity of possible components and arrangements for the implementation of agrosilvopastoral systems enhances the storage of carbon (C) in the plant biomass of pastures, of the annual crops and trees, which can mitigate greenhouse gas emissions and increase C stocks in the soil. The present study aimed to evaluate the contents and stocks of carbon and nitrogen, the dynamics of litter and soil fertility, after the conversion of low-productivity pasture into implemented agrosilvopastoral systems, in three mesoregions of the State of Minas Gerais. It was evaluated an experiment located in the municipality of Francisco Sá, in Eutrophic Haplic Cambisol, composed of a silvopastoral system, with marandu grass and Eucalyptus urograndis, nine years old, nominal pasture and native vegetation (reference area). In Curvelo, an experiment was evaluated in Red Latosol, consisting of a seven-year-old agrosilvopastoral system, nominal pasture, managed pasture and native vegetation (reference area). In Sete Lagoas, an experiment was evaluated in Red Latosol, consisting of three agrosilvopastoral systems with thirteen, eleven and nine years of implementation, an agropastoral system with thirteen years, managed pasture and native vegetation (reference area). For sampling in systems with arboreal components, three points were selected according to the distance between the eucalyptus rows, the first being in the eucalyptus tree planting line (P1), the second 3.0 m away from the tree (P2) and the third in the center of the alley (P3). The dynamics of eucalyptus litter in the integrated agricultural production system was evaluated in the Francisco Sá area through monthly collections of produced and decomposed litter over the course of a year. Soil samples were collected up to 100 cm, with the exception of the Francisco Sá area, where collection in the Haplic Cambisol was only possible to a depth of 50 cm. They were evaluated the soil density, fertility, and C and nitrogen (N) contents and stocks. In Francisco Sá (Article 1), the litter decomposition rates differed according to the distance from the eucalyptus tree lines. The CO2 efflux was influenced by the evaluation season. Higher values occurred among the months of November and February, during the rainy season, for all treatments, and P1 was statistically equal to native vegetation (VN), which had a direct correlation with the decomposition of the litter, accelerating the process by increasing humidity with greater microbial activity near the eucalyptus trees. The higher light intensities resulted in greater decomposition of eucalyptus litter and higher CO2 effluxes. Regarding nutrient contents, VN presented higher values of Ca, Mg, effective CTC and V%, a result attributed to the lack of nutrient replacement in cultivated environments and the greater efficiency in nutrient cycling in VN. The C and N stocks in the 0-50 cm depth layer were higher in VN and they did not differ between the silvopastoral system and nominal pasture. In Curvelo (Article 2), VN presented higher values for the attributes K, Ca, Mg, SB, CTC, V% and C, while, in the agrosilvopastoral system, intermediate values were observed for K, Ca, Mg, SB, CTC, V% and C. The C stocks of the different land uses did not differ from each other, in all the depths evaluated, and VN was higher than the others. In Sete Lagoas (Article 2), the highest values of pH, K, Ca, Mg, SB, CTC and V were observed in the managed pasture and P and Ds (soil density) presented higher values in the agropastoral system, intermediate values in the agrosilvopastoral and managed pasture systems and low values in VN. The managed pasture presented C stocks equal to VN and the agrosilvopastoral system at thirteen years, differing from the other uses up to 30 cm. Already in the 0-50 and 0-100 cm profiles, the managed pasture and the agrosilvopastoral systems with thirteen years presented higher C stocks than VN. The agropastoral system obtained the lowest stocks in the 0-30, 0-50 and 0-100 cm depth profiles. The N stocks did not differ between the managed pasture and VN uses, and these systems presented the highest values in relation to the other systems evaluated. Agrosilvopastoral systems are promising in storing carbon in the soil profile, and may exceed the C and N stocks of native vegetation. Therefore, they are indicated for the recovery of degraded areas, under the studied edafoclimatics conditions, as long as they are well managed throughout the production cycle.