Increasing rainfed wheat yield by optimizing agronomic practices to consume more subsoil water in the Loess Plateau

Erratic rainfall and misalignment between the rainy season and the growing season of winter wheat greatly limit rainfed winter wheat yield in the Loess Plateau of China. To increase the grain yield of winter wheat in this region, the effects of different agronomic practices, including adjusting planting pattern (NR, narrow row spacing), increasing seeding rate (high seeding rate, HS), decreasing basal nitrogen rate and increasing top-dressed nitrogen rate (DBN), and replacing an old cultivar with a new cultivar (NC) on wheat yield were investigated for two consecutive years. The results showed that the current grain yield of rainfed winter wheat in the Loess Plateau could be increased to 5879–7093 kg ha⁻¹ by HS, DBN and NC practices relative to the practice of high-yielding farmers (PF). The increased yield due to HS, DBN and NC was attributed to the higher number of spikes ha⁻¹, 1000-grain weight, and kernels spike⁻¹. Before the flowering stage, HS increased soil water consumption (SWC) in 1–3 m subsoil due to the higher plant population compared with that of PF, whereas DBN decreased SWC in the 0–2 m soil layer compared with that of PF. After the flowering stage, HS, DBN, and NC increased SWC by 8–16 mm in 2–3 m subsoil compared to PF. The water use efficiency (WUE) was increased under DBN and NC in comparison with PF. However, the WUE did not increase under HS as it had the highest evapotranspiration among the five treatments. Increasing the use of subsoil water during the late growth stage by optimizing agronomic practices or applying new cultivars with expansive roots should be the primary approach to increase rainfed winter wheat yield in this region.