Crop rotation and sequence effects on temporal variation of CO2 emissions after long-term no-till application.

Production, transport, and emission of CO2 from soil to the atmosphere are directly influenced by soil temperature and moisture conditions, exhibiting a high variability over time due to the influence of climate events and soil management practices. Thus, this study aimed to investigate the effect of summer and off-season crop residues on the temporal variation of soil CO2 emission (FCO2), soil temperature (Tsoil), and soil moisture (Msoil) under a no-till system that has been managed with the same crop arrangement for >16 years. The experiment was conducted in strips with three replications. Treatments consisted of summer crop sequences maize monoculture, soybean monoculture, and soybean-maize rotation, as well as off-season crops maize, millet, pigeon pea, grain sorghum, and crotalaria. Sixteen assessments of FCO2, Tsoil, and Msoil were carried out over 51 days. A significant effect of the interaction between time and summer crop sequences (F = 1.44; p = 0.02) and between time and off-season crops (F = 2.26; p < 0.01) was observed for FCO2. Moreover, a triple interaction was observed between summer crop sequences, off-season crops, and time for Msoil (F = 1.83; p < 0.01) and Tsoil (F = 1.32; p = 0.01). The values of FCO2 and Msoil were high on days 229 and 230 due to precipitations in the study area. The relationship between FCO2 and Msoil was positive in all the assessed management, and about 60% of FCO2 variation over the study period could be explained by soil water content variation.

Effects of long-term no-tillage systems with different succession cropping strategies on the variation of soil CO2 emission.

The optimization of conservationist production systems, whose goal is to increase carbon stocks and reduce greenhouse gas emissions, is considered one of the greatest challenges faced by agriculture nowadays. Therefore, this study aimed to assess the variation of soil CO2 emission (FCO2) and its relationship with soil attributes under long-term no-tillage systems with different successions of summer and winter crop sequences. Treatments consisted of combinations of three summer and two winter crop sequences. Summer sequences were maize monocrop (MM), soybean monocrop (SS), and soybean-maize intercrop (SM), while winter crops were crotalaria and maize. FCO2 showed no difference among summer sequences (p > 0.05). For winter crops, however, the soil under crotalaria crop residues presented higher FCO2 values (1.03 ±â€¯0.027 µmol m-2 s-1) when compared to that under maize crop residues (0.94 ±â€¯0.027 µmol m-2 s-1). Soil moisture presented the greatest influence on the temporal variation of FCO2, being correlated in the summer sequences MM (r = 0.79; p < 0.0001) and SS (r = 0.70; p = 0.002), as well as in the winter crops crotalaria (r = 0.78; p < 0.0001) and maize (r = 0.66; p = 0.005). In the Oxisol under no-tillage for >14 years, the spatial variation of FCO2 was explained by the soil physical attributes total porosity, macroporosity, microporosity, and soil temperature. The soil under crotalaria crop residues as a winter crop had an improvement in soil physical attributes, leading to a more aerated environment and hence a higher CO2 production process. However, the winter crops crotalaria (38.65 ±â€¯0.08 Mg ha-1) and maize (38.14 ±â€¯0.09 Mg ha-1) also provided a higher carbon stock on this tropical soil. Maize monocrop (41.13 ±â€¯0.11 Mg ha-1) as a summer crop under no-tillage system also promoted higher carbon stocks on this tropical soil. A strategy to optimize no-tillage systems in terms of FCO2 reduction and increase in soil carbon stock is related to the adoption of crop cultivation that includes legumes and grasses under intercropping and succession. Therefore, our results suggested that the summer sequences used in this study might contribute to reducing FCO2 and that both winter crops influenced the increased soil carbon stock.

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.