CARBON STOCKS AND MICROBIAL BIOMASS OF AN OXISOL CULTIVATED WITH SOYBEAN UNDER FUNGAL INOCULATION

Abstract

Soil organic matter is essential for the stability of natural ecosystems and the sustainability of agroecosystems. However, successive practices of plowing and harrowing, advocated in Conventional Tillage (CT) have shown reductions in organic matter, carbon stocks, and soil microbial biomass. This work aimed to evaluate the effect of different fungi on soil carbon stocks (Cs), soil microbial biomass (SMB), total organic carbon (TOC), and microbial quotient (qMic) of an Oxisol cultivated with soybean (Glycine max (L.) Merrill) under CT in the last five years. For this purpose, an experiment was conducted in the municipality of São Desidério, in Bahia, Brazil, with treatments: T1: Trichoderma asperellum + Purpurocillium lilacinus + Pochonia chlamydosporia; T2: T. asperellum isolates, and T3: without soybean seed inoculation. In the experimental plots under CT, as well as in an area of Native Cerrado (NC), adjacent to the experiment and used as a reference, undisturbed and deformed samples were collected in layers from 0.00 to 0.10 and 0.10 to 0.20 m of a Oxisol of sandy texture. In the laboratory, these samples were previously prepared and used for the quantification of Cs, SMB, TOC and qMic. Data were subjected to analysis of variance (ANOVA) and means compared by Duncan's test at a 5% probability level (p < 0.05). The results obtained showed that the fungal inoculation (T1) was not able to promote the values of Cs, SMB, TOC and qMic, probably due to alterations in the soil resulting from the time of use of the CT, when compared with the NC. The averages of the parameters in the treatments were drastically lower than in the NC, evidencing the importance of management practices that, in contrast to the CT, favor soil cover, the contribution of organic material, and promote improvements in soil quality. It is concluded, therefore, that the inoculation of soybeans with different microorganisms in the sandy Oxisol evaluated under CT was not able to increase the values of Cs, SMB, TOC and qMic.