Vertical distribution characteristics of heavy metals in agricultural soil profiles under rice-wheat system in Heigangkou Yellow River Irrigation Region

Yellow River Irrigation Region (YRIR) is one of China’s important grain production bases. The contents and chemical forms of heavy metals in the agricultural soils of the region are related to sustainable agricultural development. The distribution of main soil properties total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP) and CaCO₃₃