O efluxo de CO₂ do solo e seus componentes autotrófico e heterotrófico em áreas sob cultivo de cana-de-açúcar

Abstract

Most studies on soil respiration focus on natural ecosystems such as forests and pastures, leaving a gap in research on agricultural environments, particularly sugarcane fields. This study aimed to fractionate soil respiration (Rsoil) in sugarcane crops, quantify its microbial fraction (Rmicrobial), and identify the main factors influencing it. The research was conducted in medium- and loamy-textured areas with different cropping ages (1st and 4th cuts), structured around two main objectives: (i) evaluating the variability and methodological control of CO₂ efflux measurements (ECO₂) and (ii) fractionating Rsoil using root exclusion methods (entrenchment and sieving) and regression. The results indicated that using support rings in the closed chamber (SRC-1) significantly improved measurement accuracy and repeatability, reducing the coefficient of variation (%CV) and increasing the average ECO₂ intensity. Soil compaction between rows reduced ECO₂ by an average of 41%, compromising the accuracy of estimates. Spatial variability was low at short distances (0.10-1.0 m) but increased to %CV > 12% at longer distances. Simulated precipitation and the addition of vinasse during the dry season triggered a CO₂ emission pulse, with levels returning to baseline only after 48 hours. The entrenchment technique effectively fractionated Rsoil, especially during the rainy season and at the sugarcane maturation stage. However, sieving overestimated Rmicrobial, preventing accurate estimation of root respiration. Both Rsoil and Rmicrobial exhibited seasonal variation, with higher values observed during the rainy season, particularly in medium-textured soils and 1st-cut sugarcane fields. Regression-based microbial R estimation was feasible only in the rainy season, when sample variability was low, but requires further validation. Correlation analysis and PCA revealed that factors such as labile carbon, organic matter, moisture, macroporosity, pH, calcium, and base saturation were the main drivers of soil and microbial respiration. Soil and microbial R measurements should be taken between rows without wheel tracks and at a maximum distance of 1 meter, as compaction reduces ECO₂ values.