Effects of Surface Water Irrigation on Fertility and Properties of Agricultural Soil in the Aboveground Segment of the Yellow River Downstream

Irrigation from the Yellow River plays a vital role in supporting agricultural production within the Yellow River Basin in China. Nevertheless, few studies have focused on the impact of Yellow River water irrigation on agricultural soil around the hanging section of the river. This study surveyed the characteristics of the agricultural soil along the aboveground segment of the Yellow River spanning from Huayuankou (Zhengzhou City, Henan Province, P.R.China)—Jiahetan (Kaifeng City, Henan Province, P.R.China) section in Henan province. The soil irrigated with Yellow River water (YS), the soil irrigated with groundwater in the irrigation area (GS), and the soil outside the irrigation area (control soil, CS) were sampled and the contents and spatial variations of nutrients (involving the alkaline hydrolytic nitrogen (ASN), NH4+-N, TP, and soil organic matter (SOM), etc.), heavy metal distributions (involving Cu and Zn), and physicochemical properties (involving pH, the total water-soluble salts (Tsalts) and CEC) of the sampled soils were measured and evaluated. While collecting soil samples, the irrigation water used in soil samples was collected, including Yellow River water (YW), groundwater (GW) in the Yellow River irrigation area, and control point-groundwater (CW) at the control soil collection site, and the TN, NO3−-N, NH4+-N, TP, total salt content (TDS) and suspended matter (SS) of water samples were measured. The results indicated that the ASN, NH4+-N, TP, and SOM levels in YS were significantly higher than GS, increasing from 44.3% to 45.8%, 17.4% to 45.8%, 40.1% to 44.6%, and 7.6% to 13.6%, respectively, while the contents of Cu and Zn in YS increased from 29.3% to 34.7% and 13% to 13.5%, respectively, and the Tsalts in soil samples increased from 39.8% to 66.7%. Additionally, the pH of soil within the irrigation zone (YS and GS) was 1.8%-2.6% and 4.4%-2.6% higher than CS, respectively, which might be attributed to lateral seepage of the Yellow River. Spearman correlation analysis between soil environmental factors revealed significant associations between SOM and ASN, NH4+-N, NO3−-N, and AP (p < 0.01). Water quality analysis results indicated that the levels of TN, NH4+-N, and NO3−-N in Yellow River water were 73.5%, 15.4%, and 233% higher than the groundwater in the irrigation area, respectively. Thus, the richer N nutrition in YS soil may be related to the higher N content in Yellow River water. The results underscored the effectiveness of long-term direct irrigation with Yellow River water in enhancing nitrogen and phosphorus nutrition levels as well as organic matter content in soil. However, this practice also poses potential risks, including heightened soil heavy metal pollution (particularly Cu and Zn) and the risk of soil salinization.