Soil organic carbon storage in a sandy Cerrado Ultisol from low to high crop diversity, assessed using innovative laser-based spectroscopic techniques

Sandy soils represent a challenge for soil organic carbon (SOC) storage due to their limited clay content, which can constrain SOC stabilization. We evaluated a field experiment established in 2017 at the Mato Grosso State Cotton Institute (IMAmt), Brazil, within the Brazilian Cerrado biome, on a sandy-loam Ultisol (82.3% sand, 14.5% clay, and 0.32% silt). Five production systems with increasing crop diversity were assessed. Systems with soybean or cotton in the first season followed by fallow represented the lowest diversity, whereas the inclusion of cover crops, grasses, and animal grazing in an integrated crop–livestock system (ICLS) represented the highest diversity plot. Using laser-induced breakdown spectroscopy (LIBS) to determine soil C content, a strong linear relationship (R²= 0.85) was obtained with CHN analyzer, even for sandy samples with very low C content (0.3 to 1.3 %). Laser-induced fluorescence spectroscopy revealed a reduction in the humification index (H_LIFS) across all agricultural systems compared with native vegetation, indicating the input of newly SOC. Overall, laser-based spectroscopic techniques proved effective for quantifying SOC in sandy soils and for tracking the incorporation of new organic inputs. SOC stock showed that the highest crop diversity system (ICLS) exceeded 11 Mg C ha^-1 compared with lower-diversity systems. Additionally, SOC stocks under ICLS were more than 30 Mg C ha^-1 greater than those under native Cerrado vegetation, demonstrating that high crop diversity can substantially enhance SOC storage in sandy soils. Beyond carbon storage, three years of ICLS increased cotton and soybean productivity by 251% and 82%, respectively.