ABSTRACT Climate-smart agriculture (CSA) practices, mainly no-tillage (NT), cover cropping (CC), soil fertilization with organic amendments (OA), and crop-livestock (CL) and crop-livestock-forestry (CLF) systems, has been widely adopted in areas from Brazilian Cerrado. The CSA may partly offset former soil C losses and contribute to climate change mitigation. However, contradictory findings brought uncertainties about the effect of CSA on soil C. Here, by a systematic review of 87 papers and using 621 data pairs, we provided a pervasive biome-scale analysis of soil C stock changes associated with the adoption of CSA across Brazilian Cerrado. All CSA practices evaluated showed average positive rates of C stock change, indicating a general tendency of soil C accretion after its adoption. In areas under NT, CC and CLF, greater rates were estimated for the deeper soil profile evaluated (0.00-1.00 m) (1.24 ± 0.85, 0.54 ± 0.54 and 1.00 ± 1.47 Mg ha–1 yr–1, respectively), while OA and CL showed more soil C accretion when the assessment was limited down to 0.10 m depth (0.82 ± 0.60 and 0.59 ± 0.66 Mg ha–1 yr–1, respectively). Unfortunately, the lack of basic information precluded any attempt to statically compare our estimations. In this sense, we must be cautious in stating that soil C sequestration occurs at those rates after the adoption of CSA practices. Despite these limitations, the results clearly show that the diversification and intensification of agricultural areas in the Cerrado by the adoption of CSA is a promising pathway to increase soil C stocks, and consequently, contribute to climate change mitigation and adaptation. Finally, our findings emphasize the importance of efforts that stimulate farmers to adopt these practices on large scale, such as Brazil’s Low-Carbon Agriculture Plan, besides providing sound empirical evidence about the role of soil C sequestration in Brazil achieving its Nationally Determined Contributions commitments.

ABSTRACT To meet the growing demand for bioenergy such as ethanol, the area cultivated with sugarcane has expanded, especially in areas currently occupied by extensive pastures with low productivity. However, land-use change (LUC) from pasture to sugarcane implies changes in soil structure and variations in organic matter (SOM) stored in the soil. This study aimed to quantify the impact of LUC on organic matter fractions – particulate organic matter (POM) and mineral-associated organic matter (MAOM) – in soils with contrasting textures, and to explore the correlations between possible alterations in soil aggregation and the effects on carbon (C) stocks and SOM fractions. The study was conducted in two areas in Central-Southern Brazil, one with clayey soil and the other with sandy soil. In each area, a LUC chronosequence was evaluated: native vegetation (NV), pasture (PA), short-term sugarcane (SC1), the area analyzed during the sugarcane plant cycle; long-term sugarcane (SC2), area analyzed during the ratoon sugarcane cycle. In each use, undisturbed and disturbed samples were collected and macroaggregates and microaggregates were obtained by wet sieving and soil samples. In these samples, the physical fractionation of the SOM and the calculation of the C contained in each fraction of the SOM and C total stock of each use were performed. The conversion of NV to PA increased C stocks by more than 50 %, mainly in the MAOM fraction, and maintenance of macroaggregates (more than 80 %) in sandy site; and reduction of C stocks by more than 30 %, mainly MAOM in the clayey area. These benefits acquired from grazing on sandy area were lost with the expansion of sugarcane, a reduction of more than 20 % in macroagregation and C stocks. The sugarcane expansion into pasture with clayey site resulted in C accumulation (more than 2 Mg C ha-1 yr-1) and recovery of stocks on a SC2 basis. Expanding sugarcane areas into low-productivity pasture areas can be considered a sustainable strategy, especially in clayey soils, in which multiple gains occur through C sequestration and improved soil quality, as well as the reduction of CO2 emissions through the diversification of the energy matrix with the production of ethanol.

ABSTRACT Based on previous reports, our study aimed to obtain the first estimate on the contribution of termite mounds to CH4 emissions in Brazilian Cerrado pastures. We estimated that termite mounds occupy an area larger than 200,000 ha in degraded pastures, an important loss of grazing area considering the current scenario of land-use change of pastures to other crops in Brazil. Moreover, mound-building termites in degraded pastures may be responsible for CH4 emissions greater than 11 Mt CO2 eq. yr−1, which would notably affect the greenhouse gases (GHG) balance of grass-fed cattle production in Brazil. In this sense, it is urgent to conduct field-scale studies about the CH4 emissions by mound-building termites in pastures and its contribution to the C footprint of Brazilian beef.

ABSTRACT: The use of crop residues as a bioenergy feedstock is considered a potential strategy to mitigate greenhouse gas (GHG) emissions. However, indiscriminate harvesting of crop residues can induce deleterious effects on soil functioning, plant growth and other ecosystem services. Here, we have summarized the information available in the literature to identify and discuss the main trade-offs and synergisms involved in crop residue management for bioenergy production. The data consistently showed that crop residue harvest and the consequent lower input of organic matter into the soil led to C storage depletions over time, reducing cycling, supply and availability of soil nutrients, directly affecting the soil biota. Although the biota regulates key functions in the soil, crop residue can also cause proliferation of some important agricultural pests. In addition, crop residues act as physical barriers that protect the soil against raindrop impact and temperature variations. Therefore, intensive crop residue harvest can cause soil structure degradation, leading to soil compaction and increased risks of erosion. With regard to GHG emissions, there is no consensus about the potential impact of management of crop residue harvest. In general, residue harvest decreases CO2 and N2O emissions from the decomposition process, but it has no significant effect on CH4 emissions. Plant growth responses to soil and microclimate changes due to crop residue harvest are site and crop specific. Adoption of the best management practices can mitigate the adverse impacts of crop residue harvest. Longterm experiments within strategic production regions are essential to understand and monitor the impact of integrated agricultural systems and propose customized solutions for sustainable crop residue management in each region or landscape. Furthermore, private and public investments/cooperations are necessary for a better understanding of the potential environmental, economic and social implications of crop residue use for bioenergy production.