Biomassa microbiana e respiração basal do solo em áreas de uso forrageiro no bioma Caatinga

Abstract

In the Caatinga, livestock is the main human activity, being able to cause changes over a long time scale. Knowledge about the effect of forage use on microbial biomass in this biome is limited, however it is fundamental for understanding the flow of C and N, as well as for the elaboration of a management plan and sustainable public policies. The objective of this work is to estimate microbial biomass activity and soil basal respiration in forage use areas in the Caatinga biome after 3 years of animal exclusion. Four permanent plots of ecological studies were analyzed, implemented in the Experimental Stations of the Instituto Agronômico de Pernambuco (IPA), in the municipalities of São Bento do Una, Arcoverde, Sertânia and Araripina. In these areas, 3 permanent plots were installed, representing the main types of land use: closed caatinga, open caatinga and herbaceous pasture. The plots were fenced to prevent the entry of animals, enabling plant regeneration. The samplings for the evaluations carried out in the present study took place after 3 years of implantation of the plots. To evaluate the microbial biomass activity of the soil, the samples were repeated in the dry and rainy seasons, being collected in six random points, in the depth of 0-20 cm, being extracted as a subsample of the collected soil, for physicochemical determinations. The carbon and nitrogen of the microbial biomass were determined by the irradiation-extraction method. Basal soil respiration was determined using the alkaline absorption method. In the dry period, RBS did not differ between closed caatinga and herbaceous pasture, however it presented an increase of 12.5% in open caatinga. Seasonality did not influence the different coverages. The C-BMS did not differ between areas of open caatinga and areas of herbaceous pasture. In the dry period, the closed caatinga areas presented C-BMS 52% higher than the others. In the rainy season, there was a decrease in the levels of C-BMS in areas of open caatinga and herbaceous pasture, by 36% and 38%, respectively. In the dry period, the closed caatinga presented C-BMS 72.7% higher than the open caatinga and herbaceous pasture. The N-BMS showed no difference between the different coverages and periods. The qCO2 was low in all coverages. In the dry period there was no difference between the coverages. In the wet period, the closed caatinga areas showed lower qCO2. Seasonality influenced only the herbaceous pasture, which showed a lower value in the dry period. Therefore, in more preserved environments (closed caatinga) the biological attributes fluctuate less between periods. After three years of animal exclusion, the microbial biomass of the herbaceous pasture soil is already behaving like that of the open caatinga, showing that the Caatinga has the potential to, in a short time, restore its microbial community.