Atributos microbiológicos como indicadores de qualidade do solo em plantio de eucalipto com aplicação de biochar

Abstract

Biochar is a carbon-rich material, obtained from carbonized biomass under low oxygen atmosphere, for use as a soil conditioner. The application of biochar has the potential to change the physical, chemical and microbiological properties of the soil, increasing the availability of water and nutrients for plants. Three important strategies, however, must be associated with the concept of biochar: the recycling of organic waste, the generation of renewable energy and low-carbon agriculture. In the present work, the effect of biochar, produced from residues from the eucalyptus harvest and different doses of fertilization, on the microbial activities and enzymes of the soil of a commercial cultivation area of Eucalyptus urograndis installed in a red-yellow Latosol, in São Jerônimo da Serra, Paraná. The experiment was designed in randomized blocks with subdivided plots, varying the dose of biochar (0 or 3.23 Mg ha-1) and fertilization (0, 120 and 150 g tree-1 of the NPK formula 4: 42: 6) with four repetitions. Samples composed of soil were obtained (1) from simple samples collected near the central eucalyptus seedlings of each plot and (2) from simple samples collected randomly in zigzag in the plot. The population of bacteria involved in the nitrogen cycle was evaluated based on the determination of the Most Probable Number (NMP) of ammonifying, nitrifying and Nitrogen fixing bacteria. In addition, the activity of soil enzymes involved in the nitrogen (urease) and carbon (beta-Glucosidase) cycle was evaluated. The determination of carbon and nitrogen in the microbial biomass and the quantification of glomalin were also carried out in the first two years of eucalyptus growth and in two periods of the year. Although basal respiration did not vary between treatments at each time evaluated, it showed higher values at the beginning of eucalyptus development. Due to the greater soil stability, 2 years after planting, there was an increase in the carbon of the microbial biomass, mainly in the treatments with the application of biochar. The activity of the enzymes β-glucosidase and urease were affected by the presence of biochar, the first of which was drastically reduced over the two years of analysis, while the urease decreased its activities over the 24 months evaluated. The presence of the full dose of fertilizer did not induce an increase in urease enzyme activity. However, the urease enzyme showed a reduction in the last two sample periods, which may have influenced the soil ammonifying microorganisms, since the urease enzyme is responsible for producing ammonia from urea, thus, the decrease may be related to nitrogen availability chemical, which was applied only in the initial months of the crop.