Organic Carbon Compartments and Chemical Attributes of Sandy Soil in Response to Crop Succession Under Conventional Management and Fallow Long-term in the Semi-arid Region

This study aimed to evaluate the effects of crop succession, under both conventional cultivation and fallow management, on soil organic carbon (SOC) compartments, enzyme activity, and chemical properties of a sandy-textured soil in the Brazilian semi-arid region. The sequence of cultivation, crop succession, and fallows was as follows: 2014-Crotalaria (Crotalaria juncea L.); 2015-Corn (Zea mays L.); 2016-Cowpea (Vigna unguiculata L.); 2017-First fallow; 2018-Melon (Cucumis melo L.); 2018-Sorghum (Sorghum bicolor [L.] Moench); 2019-Second fallow; 2020-Sorghum; 2020–2022-Third fallow (COVID-19 pandemic); 2023-Melon; 2024-Corn; 2024-Cowpea. Soil samples were collected at depths of 0–10 and 10–20 cm and analyzed for total SOC, labile carbon (LC), microbial biomass carbon (MBC), particulate organic carbon (POC), humic fractions (fulvic acid, humic acid, humin), β-glucosidase activity, and chemical attributes. Multivariate statistical analyses were conducted to integrate and distinguish the responses. Results indicated that systems cultivated with corn and sorghum significantly increased SOC stocks (over 40%) and boosted LC, MBC, POC, and enzyme activity, compared to systems with melon and fallow, which experienced SOC losses exceeding 70% and suppressed enzyme activity. The Carbon Management Index (CMI) confirmed the superiority of grass-based systems in terms of sustainability. These findings emphasize the potential of diversified, residue-rich cropping systems to restore biological functionality and improve organic matter quality in degraded sandy soils under semi-arid conditions.