Soil carbon fractions and aggregate stability across management zones under flood-irrigated pecan orchards in an arid region

Soil organic carbon (SOC) dynamics in arid regions are influenced by climatic and edaphic factors; however, limited research has assessed how flood irrigation affects carbon fractions and their role in stabilizing soil aggregates in pecan orchards. This study evaluated the impact of three management zones, such as tree root zone (RT), inter-row (IR), and bare land (BL), on soil physical and chemical properties in a pecan orchard in El Paso, Texas. At the 0–15 cm depth, soil organic carbon (OC) and permanganate oxidizable carbon (POXC) were significantly higher in RT by 90.2% and 50.1%, than in IR. These differences were even more impressive with depth: at 15–30 cm, OC and POXC in RT were 124.6% and 97.2% higher than IR. Water-stable aggregates across all size classes were significantly higher under RT and BL compared to IR at all depths (0–75 cm). At 0–15 and 15–30 cm, the RT zone had significantly greater >2 mm by 48.6% and 70.2%, respectively, than the IR zone. At 0–15 cm, the 0.5 and 0.25 mm aggregate fractions contained significantly higher total carbon (TC) than the 1 mm and >2 mm fractions. At 15–30 cm, OC in the RT zone was higher than in the IR by 49.2% and 34.5% in the >2 mm and 1 mm aggregate fractions, respectively. In contrast, IR showed greater soil inorganic carbon (SIC) at 15–30, 30–45, and 60–75 cm. In all management zones, Olsen-P in the 0–15 cm layer was higher than in the 30–70 cm layer. Positive significant correlations between >2 mm aggregates and TC, OC, POXC, clay, silt, CEC, Olsen-P, and exchangeable cations suggest that organic matter inputs from pecan roots and leaf litter enhance soil structural stability. These findings indicate that increased OC and POXC in the RT zone contribute to improved soil resilience under arid conditions. • Tree root zones had higher > 2 mm water-stable aggregates than inter-row zones. • >2 mm aggregates positively correlated with TC, OC, POXC, and available nutrients. • Flood irrigation led to deeper SIC and salt accumulation in inter-row zones. • SOC increased in 0.5 and 0.25 mm aggregates, enhancing carbon stabilization.