Effects of wheat in regulating runoff and sediment on different slope gradients and under different rainfall intensities

Wheat (Triticum aestivum L.) is widely planted on China's Loess Plateau, where severe soil erosion mainly occurs on sloping farmlands. However, whether wheat regulates runoff and sediment in this region is not completely understood. This study investigated the effects of wheat for regulating runoff and sediment across different slope gradients and rainfall intensities in the Loess Plateau region. The experimental design included six growth stages of wheat (tillering, early stem extension, late stem extension, heading, ripening and stubble stage), five slope gradients (8.7, 17.6, 26.8, 36.4 and 46.6%), and three simulated rainfall intensities (60, 90, 120 mm h(-1)). The effects of wheat were divided into three parts: delayed runoff generation, reduced runoff, and reduced sediment. Wheat's performance was assessed using time to runoff, initial loss of rainfall, runoff volume, sediment yield, time delay benefit (TDB), runoff reduction benefit (RRB), and sediment reduction benefit (SRB). The results showed wheat excelled at regulating runoff and sediment. From the tillering to ripening stage, wheat reduced the runoff by 43.8-83.4% and the sediment by 86.7-98.2% when compared with bare ground; even wheat stubble was able to reduce runoff (by 35.7%) and sediment (by 68.2%). Values of TDB, RRB, and SRB for wheat were all directly proportional to its vegetation coverage and inversely proportional to the slope gradient. Similarly, wheat's TDB and RRB were inversely proportional to rainfall intensity but its SRB was not significantly influenced by it. Since their SRB values always exceeded the RRB, both wheat and stubble were found more effective at reducing sediment than reducing runoff. Vegetation coverage was the main factor affecting the TDB, RRB, and SRB of wheat, in that greater coverage particularly decreased the sensitivity of RRB and SRB to changes in the slope gradient. In conclusion, wheat is suitable for cultivation in erosion-prone areas with abundant sloping farmland resources and heavy rainstorms.