Atmospheric CO2, soil carbon stock and control variables in managed and degraded pastures in central Brazil

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Brazil has 166 million hectares of pastures, 58.8% (97.6 million hectares) of which are in some degree of degradation. Besides the low animal support capacity and vegetative yield, degraded pastures also contribute significantly to soil carbon losses, through CO2 emission. This study aimed to understand the temporal dynamics of atmospheric CO2 in contrast between degraded pastures (DP) and managed pastures (MP) in the Cerrado Brazil biome. Using the Pasture Atlas and 6-year time series, the variables were collected under the pasture classes: column-average concentration of carbon dioxide in the atmosphere (xCO2), Soil Carbon Stock (SCS), as well as Solar-induced Chlorophyll Fluorescence (SIF), Normalized Difference Vegetation Index (NDVI) and Leaf Area Index (LAI) as vegetative characteristics, and Land Surface Temperature Amplitude (LST Amplitude) and Precipitation as climatic aspects. Except for xCO2, MP was significantly different from DP with higher SIF, NDVI, LAI, Precipitation, and SCS, but smaller LST Amplitude. The hypothesis test (Student t-test p < 0.05) results indicate higher Precipitation and SCS in MP when compared to DP due to its positive effect of higher vegetative values. Linear regression and Pearson's correlation analysis indicate that xCO2 negatively relates to the precipitation and vegetative variables (NDVI, LAI, and SIF), but positively with LST Amplitude and SCS. Soil carbon stock obtained a significant xCO2 relationship (p < 0.001) only in the DP, suggesting that the environmental stress experienced by degraded pastures impacts soil carbon losses as a source of CO2. Therefore, this study concludes that DP with carbon stored in the soil is the main source of CO2 for the atmosphere when compared to MP. So, if the necessary care is not taken, the organic carbon from these degraded pastures will be lost to the atmosphere as CO2. These findings may favor nature-based solutions indicating that proper pasture management is an important aspect to mitigate emissions and improving soil carbon content helping to mitigate atmospheric CO2.