Long-term effect of sediment laden Yellow River irrigation water on soil organic carbon stocks in Ningxia, China

• Long-term effect of sediment laden Yellow River irrigation water on soil organic carbon stocks was significant in Ningxia, China.
• SOC density and SOC stocks increased with increasing duration of irrigation.
• The SOC content increased partly due to the addition of soil clay content by irrigating with sediment laden Yellow River water.
• The irrigation-silted soil layer plays an important role in soil carbon sequestration.

Given the positive effects of mediating the growth of greenhouse gases in the atmosphere, interest in soil carbon stock dynamics has greatly increased. Several questions still exist as to whether irrigation with sediment laden water benefits carbon sequestration in soil profiles. This case study documented how long-term irrigation with sediment laden water from the Yellow River affected soil carbon sequestration in the Ningxia Irrigation Zone, China. The study included eight durations of irrigation management (10, 20, 30, 50, 280, 1300, 2100, and 2200 years) and five soil types. Soil samples from 44 profiles were collected to a depth of 100 cm, divided into four layers (0–20, 20–30, 30–60, 60–100 cm), and analyzed for soil organic carbon (SOC). SOC stocks both of soil profiles (0–100 cm) and irrigation-silted soil (ISS) layer, were 28.2 Tg C and 24.1 Tg C, respectively. The ISS layer was formed by the overlapping actions of irrigation and tillage, manure addition, and sediment silting as a result of long-term irrigation from the sediment laden water of the Yellow River. Compared to non-irrigated and non-cultivated control soils of similar depths and thicknesses, SOC stocks of the ISS layer increased 16.9 Tg C, and accounted for 89.9% of a total increment of 18.8 Tg C in the 0–100 cm layer of irrigated cropland soils. A significant correlation was found between the SOC density increment of the ISS layer and the number of irrigation years. Long-term irrigation with sediment laden Yellow River water greatly influenced SOC stocks, especially in the ISS layer, which plays an important role in soil carbon sequestration.