Effect of crop type shift on soil C:N:P stoichiometry in a typical Yellow River irrigated district

The Hetao irrigation area is one of the largest irrigation areas in the Yellow River Basin and is a typical salinized agricultural area. Crop type shifts can affect soil stoichiometric ratio characteristics, indicating soil nitrogen and phosphorus availability and the soil degradation process. However, few studies have been conducted in this area. In this study, soil samples were collected at 45 sites under sunflower fields (SF) and other land (OL), and the SF were mostly shifted by the OL. The results revealed that the soil pH and salinity clearly increased while the OL shifted to the SF. Moreover, soil organic matter (SOM), total nitrogen (TN), and total phosphorus (TP) also decreased significantly. These findings indicate that the soil degradation process accelerated during crop type conversion. Moreover, with the transition from OL to SF, there was little difference in the C: N ratio, whereas the C:P and N:P ratios decreased significantly. The soil P mineralization rates increased, and the N limits improved during the crop type shift. In addition, the soil C:N, C:P, and N:P ratios decreased overall with increasing soil depth. This research provides new insight for the management of crop types and the improvement of soil properties in the saline‒alkali soil of the Yellow River irrigation area.