Abstract: Irrigation is an important strategy to ensure agricultural production, with consequences on soil physicochemical properties. We examined the effects of irrigation on soil organic carbon fractions and other soil properties in the Ningxia Irrigation Zone, which was irrigated by the sedimentladen Yellow River water. Compared to control treatment (non-irrigated and non-cultivation soil), irrigation significantly increased total soil organic carbon, heavy and light fraction organic carbon by 272%, 222% and 318%, respectively. Heavy fraction organic carbon was a major part of the total organic carbon, accounting for >65% of total organic carbon. The higher content of heavy fraction organic carbon, the more stable the soil organic carbon pool was. After cultivation and irrigation with Yellow River water, soil total N and P significantly increased from 0.27 and 0.85 g·kg^-1 to 0.77 and 1.68 g·kg^-1 (P<0.05), respectively. Soil aeration and water retention were enhanced, the salinization degree and soil pH were reduced, and soil fertility was promoted by irrigation with sedimentladen Yellow River water. Overall, irrigation with Yellow River water is an effective strategy to improve soil properties and land productivity in this region.

Key words: geographically weighted regression, forest carbon storage, ordinary least square, geographically weighted regression Kriging, spatial heterogeneity.