Indicadores microbiológicos em sistema silvipastoril com leguminosas em ambiente tropical subúmido

Abstract

Cattle raising in Brazil is mostly based on extensive pasture usage, and frequently lead to their degradation. Silvopastoral systems are a sustainable management alternative, used to reduce environmental impacts related to cattle raising introduction, while at the same time increasing its productivity. Tree presence in this system, besides promoting heterogeneity in forage quality and offer, increases soil microbiological quality and nutrient cycling. Due to this, this work aims to understand how the introduction of legume trees in pasture systems affects soil microbiological quality indicators in a sub-humid tropical environment. Data was collected from an experiment with three treatments: i) pure signal grass (Brachiaria decumbens Stapf.), ii) signal grass with gliricidia (Gliricidia sepium Jacq. Steud) and iii) signal grass with sabiá (Mimosa caesalpiniifolia Benth). Soil samples were collected at the dry and rainy seasons, at the 0-20 cm depth layer at 0, 4 and 8 m from the legume rows, and as a random sample in the single signal grass and used to determine microbial biomass P content, easily extractable and total glomalina contents, enzymatic activity of acid and alkaline phosphatases, urease and arylsulfatase, as well as real time PCR quantification of genes for microbial atmospheric carbon fixation, total and mycorrhizal fungi, and linked to phosphorus mineralization. The rainy season presented higher microbial activity in the silvopastoral systems, increasing microbial biomass P content, acid and alkaline phosphatases and arylsulfatase activities, while urease activity was higher for single signal grass in both seasons. Higher copy number abundance was also found for CO2 fixers, total and mycorrhizal fungi and phosphorus mineralizers in the rainy season for the silvopastoral system, except at both legume rows. No effect of the silvopastoral system was found for glomalin concentrations. Legume silvopastoral systems increased soil biological quality, and potential atmospheric CO2 drain through carbon microbial fixation. Gliricidia established the best conditions for maintaining signal grass. Rain affected enzymatic activity and microbial community abundance, being an important parameter for the evaluation of silvopastoral system quality.