The use of different coverages crop manegement in sugarcane field reform on humic substances contents and chemical attributes of a sandy soil

Sugarcane cultivation, a major activity in the Brazilian sugar-energy sector, is commonly established on low-fertility sandy soils. Improving soil organic carbon stocks and humic substances is essential to enhance soil quality and sustainability. This study evaluated the effects of different cover crop managements during sugarcane field reform on organic carbon, humic substances, and chemical attributes of a sandy Ultisol. The experiment was conducted in a commercial area using a completely randomized design with four treatments—conventional planting, soybean cover crop, Crotalaria spectabilis cover crop, and native forest as reference—and three replicates. Soil samples were collected 12 months after sugarcane planting (0–10 cm) and analyzed for organic carbon, fulvic and humic acids, and chemical attributes. Data were subjected to analysis of variance (ANOVA), Tukey’s test (p ≤ 0.05), and Pearson correlation analysis. The use of Crotalaria spectabilis significantly increased organic carbon and humic substance contents, reaching levels similar to the native forest, while soybean cover showed no improvement compared to conventional management. Increases in organic carbon and humic substances were positively correlated with potassium availability and negatively correlated with soil pH and phosphorus availability. The results demonstrate that Crotalaria spectabilis is an effective cover crop during sugarcane field reform, promoting improvements in soil organic fractions and chemical attributes, contributing to more sustainable sugarcane production in sandy soils.