Effects of different intercropping patterns on soil organic carbon content, enzyme activity, and aggregate stability in Apple orchards on the loess Plateau

This study aimed to investigate the impacts of distinct intercropping patterns on soil quality in apple orchards located on the Loess Plateau. Despite the recognized benefits of intercropping, systematic research on apple-onion and apple-rapeseed systems remains limited, particularly regarding their combined influence on soil organic carbon fractions, aggregate stability, and enzyme activities under arid conditions. Four distinct planting configurations were implemented in the orchard: conventional tillage between rows (CT), natural grassing between rows (NG), intercropping onions between rows (IA), and intercropping rapeseed between rows (IR). A three-year field trial was conducted to thoroughly examine alterations in soil physical characteristics, carbon and nitrogen concentrations, enzymatic activities, and aggregate stability. Our findings demonstrate that, enhance soil quality. Notably, the NG, IA, and IR treatments notably increased soil organic matter content (up to 40.04% under IA) and a reduction in soil bulk density (13.19% under IA) within the top 0-20 cm soil layer. The IA treatment recorded the highest levels of total organic carbon and its fractions, likely due to the dense root system of onions enhancing microbial activity and organic matter input. Concurrently, the IR prominently bolstered the mechanical and hydraulic stability of soil aggregates (e.g., 160.72% increase in WR0.25), thus enhancing overall soil structural integrity. Furthermore, various intercropping configurations differentially influenced soil enzymatic activity, with NG demonstrating optimal β-glucosidase (βG) and cellobiohydrolase (CBH) activities, IA excelling in N-acetyl-β-D-glucosaminidase (NAG) and leucine aminopeptidase (LAP) activities, and IR standing out in xylanase activity. This study provides the first comprehensive evaluation of intercropping effects on soil carbon sequestration and structural stability in arid apple orchards, offering novel insights into optimizing sustainable soil management practices. In summary, the IA and IR intercropping models demonstrate a pronounced capacity to improve orchard soil quality, highlighting their potential as a scientific foundation for enhancing soil fertility and ensuring sustainable development of dryland apple orchards in ecologically fragile regions.