Initial guidelines and constraints for integrated systems to promote soil carbon sequestration in Brazil's semi-arid region

Different regions in Brazil have recommended integrated crop-livestock-forest systems (ICLF) as an efficient strategy for soil organic carbon (SOC) sequestration. In the Brazilian semi-arid region, the climate and soil management conditions suggest that enhancing SOC storage via ICLF systems will be more challenging than in other regions. The study aimed to evaluate different integrated systems to identify which arrangements, crops, and soil management practices support the sustainability of integrated systems for enhancing SOC sequestration in the Brazilian semi-arid region. We assessed integrated livestock-forest (ILF) systems in Ceará and Sergipe states, Brazil. In Ceará, the treatments consisted of sorghum, forage cactus, massai grass, and buffel grass, all with 6 years of duration, arranged at varying spacings of 7, 14, and 28 meters between native tree strips that were 6 meters wide, alongside an area of native vegetation (NV). We conducted the sorghum treatment using conventional tillage (CT), while the others used no tillage (NT). In Sergipe, NV, an ILF with 8 years comprising gliricidia+urochloa under NT (ILFug), an ILF with 10 years consisting of gliricidia+forage cactus under CT (ILFcg), an improved and a degraded pasture, both with 15 years, were selected. In Ceará, the main findings were: i) In the 0-30 cm layer, systems with massai (28 m) and buffel grasses (14 m) had higher SOC stocks by 9.6% and 10.4%, respectively, compared to the 7 m spacing; ii) massai and buffel grasses had the least SOC losses compared to NV; and iii) CT clearly limited the potential carbon gain in the sorghum treatment. The Sergipe experiment demonstrated that NT alters the accumulation of SOC. ILFug, managed under NT, showed a 77.3% increase relative to ILFcg under CT and a 16.6% increase compared to NV in the 0–30 cm layer. It is noteworthy that in both tests, the use of fodder cactus yielded the least favorable outcomes regarding SOC buildup. Consequently, these are preliminary findings that suggest factors that may restrict or augment the impact of ILF systems on SOC sequestration in the Brazilian semi-arid region. The results indicate that the spacing of tree components affects SOC dynamics; crops with high biomass production should be prioritized; palm cultivation should be intercropped with crops that yield greater biomass; and soil management must be conducted under a no-tillage system. These outcomes are directly associated with a sustainable use of soil in the semi-arid region, as well as with SDGs 13, 2, and 1.