Crop rotation and succession in a no-tillage system: Implications for CO2 emission and soil attributes.

This study aimed to quantify and characterize the relationship between soil CO2 emission (FCO2) and soil physical, chemical, and microbiological attributes at the end of the agricultural season in an area under a no-tillage system with crop rotation for more than 16 years. Summer crop sequences consisted of corn and soybean monoculture and corn-soybean rotation. Winter crops were corn, millet, pigeon pea, grain sorghum, and crotalaria. Treatments consisted of combinations of three summer crop sequences with five winter crops. Sixteen assessments of FCO2, soil temperature, and soil moisture were carried out under the remaining straw from the combination of summer sequences and winter crops over a 51-day period. Subsequently, soil physical, chemical, and microbiological attributes were assessed at depths of 0-0.10 and 0.10-0.20 m. The experiment was conducted in strips in a randomized block design with three replications. The multivariate analysis showed that the characterization of the pattern of FCO2 and other soil attributes as a function of the management with summer and winter crop residues differed according to the soil layer. In the 0.10-0.20 m layer, no difference was observed between treatments. However, the contents of clay, organic matter, sum of bases, microbial biomass carbon, dehydrogenase and amylase enzyme activity, and humification index of organic matter in the most superficial soil layer (up to 0.10 m) contributed to characterize differences in FCO2. Therefore, FCO2 variation is more influenced by soil microorganisms and the management in the most superficial layer. Soil attributes such as organic matter, enzyme activity, and biomass carbon had a higher influence on FCO2 dynamics in the 0-0.10 m layer, while soil density became a significant factor in FCO2 variation in the subsurface layer (0.10-0.20 m). Strategies such as soil management under no-tillage systems can be considered very efficient because, regardless of the residues generated by different crops, it contributes significantly to reduce FCO2, assisting in mitigating greenhouse gases in agriculture. Further studies on soil metagenomic analyses with quantification of functional genes related to carbon cycle will allow establishing direct relationships between FCO2 and microbiota dynamics and soil management since microbiota is the most sensitive bioindicator to changes in the environment.