Diversidade bacteriana em solos cultivados com diferentes plantas de cobertura sob sistema plantio direto e convencional em unidade de produção orgânica

Abstract

An alternative to the Conventional Tillage (CT) for promoting higher conservation of agricultural soils is the adoption of No-tillage (NT). In this context, cover crops are fundamental in the production of straw and release nutrients in the soil, directly influencing microbial populations. Thus, the objective of this work was to evaluate the bacterial diversity in soils under CT and NT with different cover plants in an organic production unit in the municipality of Seropédica-RJ, Brazil. The experiment was conducted in a randomized block design with two plots (CT and NT) with four replications. The black oat was sown in the total area. When the cut point was reached, the black oat was incorporated or maintained on the soil surface. Then, the corn was sown in all plots. The soil was collected in the initial time, after the black oat and after corn harvesting in a depth of 0-5 cm. Experiment II was conducted in a factorial design (2 x 6) with subdivided plots, with 2 plots of CT and NT, 6 subplots with cover plants (pearl millet, sunn hemp, jack beans, cocktail 1 and cocktail 2, using 100 and 50 % of the recommended amount for each species, respectively, and spontaneous plants), with 4 repetitions. The soil was collected after the cultivation of cover plants at a depth of 0-5 cm. Chemical characterization and extraction of total soil DNA were carried out for the sequencing of the Bacteria rrs gene. In experiment I, between the initial characterization and the corn crops in CT and NT, an increase in the phosphorus content and a decrease in carbon, an increase in the alpha-diversity indexes and a change in the bacterial composition was observed, mainly in relation to the candidate for division WPS-1, which had an increased relative abundance, and the Micrococcaceae family, which showed a decrease in its relative abundance after conversion to the agricultural area. After corn, potassium was higher in CT, and Spartobacteria unclassified and Chitinophagaceae were more abundant than in NT. In experiment II, the cultivation of different cover crops did not promote changes in the soil's chemical attributes. The cultivation of spontaneous plants supported a higher bacterial alpha-diversity index concerning sunn hemp. Jack beans and cocktails 1 and 2 promoted a higher relative abundance of the Sphingomonadaceae and Bradyrhyzobiacae families. At the same time, spontaneous plants resulted in a higher relative abundance of unclassified bacteria and the Planctomycetaceae family. Therefore, the conversion from pasture area to agricultural production area led to an increase in diversity and alteration in the structure of the soil bacterial community. There was no difference in the alpha-diversity indexes between CT and NT, but the structure of the bacterial community was altered. Different cover plants promoted differences in the structure of the bacterial community, and spontaneous plants promoted a higher alpha-diversity index concerning sunn hemp.