Evolutionary process of soil grain-size fractals in irrigation areas of northern China: a pedological analysis of ancient irrigation wisdom

As a fundamental cornerstone for sustainable societal development, soil formation and evolution play crucial roles in ensuring food security and agricultural advancement. This study investigated the mechanisms underlying the effects of long-term silt-laden irrigation on soil multifractal characteristics through a case study of the Jinghui Canal irrigation district, an ancient irrigation system. Distinct evolutionary patterns of soil multifractal characteristics were systematically analyzed through fractal theory integrated with self-organizing mapping, combined with the developmental history of the irrigation district. The results demonstrated widespread multifractality in the irrigated soils, with parameters exhibiting significant spatiotemporal heterogeneity. Spatially, narrower grain-size distribution ranges were observed in soils adjacent to northern and southern canal systems, whereas central canal areas exhibited broader distribution ranges (D(0) with maximum mean value: 0.99) and improved uniformity (minimum mean Δα: 1.52). The self-organizing mapping clustering categorized 45 sampling sites into five groups (C1–C5), with central canal soils (C1 and C5) demonstrating superior uniformity. Temporally, soil profiles under long-term irrigation exhibited stable multifractal parameters, as exemplified by the coefficient of variation being merely 3% for these parameters within specific burial depth ranges around the central canal system, whereas regions (C2, C3 and C4) with intermittent irrigation demonstrated variable uniformity with poorer homogeneity. Irrigation practices facilitated fine-particle enrichment, increasing D(1) and D(2) while reducing Δα, indicative of enhanced soil structure and nutrient retention. Conversely, irrigation reduction induced sandification, increasing D(1)/D(0) and decreasing Δf(α). These findings underscore that consistent irrigation promotes soil homogenization and fertility enhancement, whereas irrigation discontinuity amplifies structural heterogeneity. This research provides scientific insights for optimizing irrigation strategies, improving soil productivity, and advancing sustainable agricultural practices.