Estoque de carbono e atividade microbiana em sistemas silvipastoris na zona da mata de Pernambuco

Abstract

The conversion of native vegetation áreas into pastures may contribute to the emission of greenhouse effect gases, due to the soil use change. The use of silvopastoral systems, which integrate legume tree species and grasses, may be a viable option to mitigate these emissions and increase soil carbon and nitrogen stocks. This work aimed to evaluate carbon stock (EC) and microbial activity in silvopastoral systems in the Forest Zone of Pernambuco. To this end, soil samplings were done at the dry and rainy seasons in an experiment evaluating signal grass (Brachiaria decumbens Stapf) with sabiá (Mimosa caesalpiniifolia Benth) or gliricidia (Gliricidia sepium (Jacq.) Steud.). Soil samples were taken up to 100 cm depth at 0, ,4 and 8 m from the legume strip, and up to 20 cm at 0,2,4,6 e 8 m from the legume strip for biological analysis. Total organic carbon (COT), total nitrogen (NT), soil organic matter chemical fractioning (fractions fulvic acid – AF; humic acid – AH and humin –HUM), soil density, microbial biomass carbon (Cmic), soil basal respiration (RBS) were determined and metabolic quocient (qCO2) and carbon stock (EC) were calculated. There was no significant difference (p>0.10) for Cmic for the distances from the legume strip at the rainy season. Significant difference was found for RBS at the rainy season for legume strip distances and soil depth layers. There was no significant difference (p >0.10) for Cmic between legume strips distances for the rainy season, while there was significant differences (p<0.10) for RBS between legume strip distances and soil layers. At the dry season, the highest qCO2 was at the 0-10 cm layer, 2 m away from the legum strip. There was significant difference between systems and legume strip distances for COT at the dry season, with the highest contents at 8 and 4 m for gliricidia and sabiá, respectively. EC had significant differences (p<0.10) between soil layers at the dry season, with higher values at the 20-60 layers, while at the rainy season there was only a significant difference at the 0-10 layer at 8 m from the legume strips, when sabiá values were 33% higher than gliricidia ones. Significant difference (p<0.10) was found for NT between layers on both seasons, with higher values going from the upper to the deeper layers. In general the AF fraction was the smallest, with higher values for all three fractions (AF, AH and HUM) for sabiá. Biological activity, as represented by Cmic and RBS, confirmed the silvopastoral systems capability of maintaining soil microbiota. The the higher C content in more stable fractions in sabiá indicates it to be more efficient in carbon sequestration. The silvopastoral system had EC similar to other cropping systems, but it might increase in a longer term of evaluation.