Losses and gains of soil organic carbon in grasslands in the Brazilian semi-arid region

Soil Carbon Stocks and Compartments of Organic Matter Under Conventional Systems in Brazilian Semi-Arid Region

“…In the Brazilian semi-arid region, land-use change occurs through deforestation and burning of native vegetation (NV) known as "Caatinga", followed by conventional soil tillage for implementing rainfed agriculture, usually by smallholders who cultivate short-cycle crops, in parallel with extensive livestock farming (MEDEIROS et al, 2020). In addition, this region has short and irregular periods of rainfall and high evapotranspiration and temperature, which limits the production of plant biomass and hampers soil organic matter (SOM) accumulation in these systems (MEDEIROS et al, 2021).…”

“…In the surface soil layer, normally there is greater supply of C by roots and litter, but also greater microbial activity and higher SOM mineralization rates compared to deeper layers (BLÉCOURT et al, 2019) and are due to the major disturbances that occur in this layer (SANTANA et al, 2019). For example, in the pasture area, these impacts are related to the pressure exerted by the animals (OLIVEIRA et al, 2016), which compacts the soil, reducing water infiltration and soil aeration and limiting root development, consequently, the input of SOM (MEDEIROS et al, 2021), and in agricultural areas these impacts are related to conventional management techniques, mainly the soil tillage and decrease of organic matter input (MEDEIROS et al, 2020). This effect has also been observed by de Blécourt et al (2019) in semi-arid southern Africa, as well as in other Brazilian regions by Kantola, Masters, Delucia (2017), andSantos et al (2011), who indicated higher losses of C in the surface layer of the soil.…”

“…However, the large increase in the POM fraction in the RRPa10 area occurred probably due to the absence of constant soil tillage, as happens in agricultural areas (SALTON et al, 2011), the release of root exudates from grasses (OLIVEIRA et al, 2016), greater production of plant residues and thin roots with easier decomposition (SANTANA et al, 2019). In addition, this increase in POM in the pasture area must be related to the amount of biomass in this system (MEDEIROS et al, 2021), since according to Sampaio and Costa (2011), native pasture in the Brazilian semi-arid region has an input of 6 Mg ha -1 year -1 of aboveground biomass, 2 Mg ha -1 year -1 of belowground biomass and fixation of 120 Tg year -1 of C in the biomass, which is greater than the aboveground (4 Mg ha -1 year -1 ) and belowground biomass input (1 Mg ha -1 year -1 ) and C fixation in the biomass (38 Tg year -1 ) in the area of annual crops. These data confirm the differences in POM results found in this study.…”

Responses of soil greenhouse gas emissions to land use conversion and reversion—A global meta‐analysis

“…There was compelling evidence that natural forest and herb were important CH 4 sink and the reversion to them could still promote CH 4 uptake, and the function of CH 4 sink became prominent as the ecosystem gradually stabilized. And soil SOC in forest and grassland grew higher than the former land uses as time went on (Figure S4e; Table S3), because the reversed vegetation protection promoted the organic carbon accumulation (Feng et al, 2022; Medeiros et al, 2020). The ascending CH 4 uptake was accompanied by relatively high SOC in the reversed land uses because its flux would decrease with the increase of organic carbon in forest soil (Gatica et al, 2020).…”

Plant biotype interacting grazing activity shapes grassland ecosystem functions

“…Livestock grazing has been identified as a primary anthropogenic factor affecting grassland ecosystem services worldwide (Donovan & Monaghan, 2021; Teutscherova et al, 2021; Venter et al, 2021). Overgrazing—grazing for extended periods without sufficient vegetation recovery—causes a reduction in net primary production (Donovan & Monaghan, 2021; Wei et al, 2022), soil compaction as a result of animal trampling (Julich et al, 2022), the depletion of topsoil fertility and the reduction of water infiltration (Panahi et al, 2021), loss of soil organic carbon (SOC) (Medeiros et al, 2021), and heightened risks of soil erosion (Donovan & Monaghan, 2021; Panahi et al, 2021). In the past decades, relevant policies with strict regulations have been implemented in many regions/countries to regulate grazing activity and restore degraded grassland ecosystem services.…”