Carbon stocks and microbial activity in a consolidated no tillage system in Southern Brazil

Abstract

The analysis of soil quality is an important tool to evaluate ecosystems, and to plan and adopt practices of sustainable agricultural management. Thus, the objective of this study was to evaluate the carbon stocks and microbial activity under different management practices in a long-term experiment with disturbed and undisturbed soil samples. The experiment is installed in a Ultisol, in a no tillage system for 11 years with variable inputs of crop residues during winter (0, 2, 4, 6 and 8 Mg ha^-1) and in the summer with crop rotation (corn/soybeans or beans). The soil organic carbon stocks (SOC), and the coefficients of humification (k₁) and decomposition (k₂) of the soil organic matter were determined. The microbial basal respiration (CO₂-C) in disturbed and undisturbed soil samples, and the levels of microbial biomass carbon (MBC) and metabolic quotient (qCO₂) were also quantified. The SOC ranged from 21.3 to 27.3 Mg ha^-1 , whereas the addition of less than 6 Mg ha^-1 of crop above ground maintained the SOC below the original condition (24.4 Mg ha^-1). The k₁ and k₂ values were higher than those found in the literature for the same soil. The MBC exhibited higher value to inputs of 8 Mg ha^-1 of residues, whereas the qCO , although it was significant higher value for the lowest supply of residue. The CO₂-C was not significantly different between disturbed and undisturbed samples in each treatment. However, significant differences between treatments were showed in the undisturbed samples. While our results of microbial activity showed that the use of undisturbed samples can be used for this determination, more studies are needed to improve this technique.