Comunidade microbiana do solo e atividade enzimática em um latossolo subtropical sob plantio direto de longa duração e rotação de culturas

Abstract

The development and selection of agricultural practices are one of the main challenges for the sustainability of agroecosystems in response to the increased demand for food. Thus, mediate agricultural practices based on conservation agriculture, characterized by minimal soil disturbance (e.g., no-till - NT), permanent soil cover, and crop rotation can promote an improvement in the soil microbial community in comparison with tilled soils. However, NT is often used without the other principles of conservation agriculture in South America. Thus, the combination of NT and increasing crop rotation diversity may enhance the soil microbial community and enzymes activity. In this way, we hypothesized that no-till adoption without crop diversification, a practice used in large scale in South America, won’t be able to increase the soil microbial biomass and activity. The long-term experiment was established at the CCGL-TEC in Cruz Alta, state of Rio Grande do Sul, Southern Brazil, in a Typic Hapludox. The climate was classified as humid subtropical (Cfa) with average annual precipitation of 1774 mm and the average temperature of 25ºC. The experiment consisted of two soil management systems: no-tillage (NT) and conventional tillage (CT), and three crop rotation systems. Soil samples were taken at 0 to 5, 5 to 10, and 10 to 30 cm. The soil microbial community was accessed by phospholipid fatty acid analysis (PLFA). We used a fluorometric method to evaluate β-glucosidase, acid phosphatase, and N-acetyl-glucosaminidase activity as biomarkers of C, N and P cycling. The highest microbial biomass was reported at 0 to 5 cm layer under NT (40.19 nmol PLFA g-1 soil), whereas CT was 25.41 nmol PLFA g-1 soil. On another hand, soil microbial biomass was augmented in deeper soil layers (10 to 30 cm) of the CT soil. The higher abundance of microbial groups in the 0 to 5 cm and 10 to 30 cm layers of respective NT and CT soils were correlated with increased C and nutrient levels (N, Ca2+, Mg2+) and decreased Al3+ concentrations, as a result of plant residue and nutrient retention on the surface of NT soils and incorporation within the plow layer in CT soils. Moreover, the association of NT and increased crop rotation augmented the activity of β-glucosidase, acid phosphatase, and N-acetyl-glucosaminidase in the topsoil. Nevertheless, differences among cropping systems decreased with soil depth and were discrete under CT. Our results suggest that the increase in crop diversity favored the abundance of both microbial communities and extracellular enzymes activity in the surface of NT soils.