Enhancing wheat yield and nitrogen use efficiency in the Huang-Huai-Hai region of China: Insights from root biomass and nitrogen application responses

Wheat yield and nitrogen use efficiency (NUE) have improved simultaneously with the genetic development of wheat varieties. However, wheat selection is carried out routinely in N-rich field conditions, with breeding progress limited under low soil available nitrogen. Thus, we performed a 2-year field investigation using eight milestone winter wheat varieties released between 1947 and 2017 in the Huang-Huai-Hai region of China with two N applications—normal (CK; 220 kg N ha⁻¹) and reduced (RN; 110 kg N ha⁻¹)—in Shaanxi, China, to examine changes in wheat yield, NUE, water use efficiency (WUE) and root biomass. Our findings revealed average annual yield increases of 49.615 kg ha⁻¹ and 36.905 kg ha⁻¹ under CK and RN, respectively. Notably, the NUE trend mirrored yield, increasing with the release year of wheat varieties, with average annual increases in NUE of 0.192 and 0.336 kg kg⁻¹ under CK and RN, respectively. In the RN treatment, N uptake efficiency (UPE) increased with year of release, while N utilization efficiency (UTE) had no significant relationship. In the CK treatment, UTE increased with year of release, while UPE had no significant relationship. Across the 2-year experiment, surface root biomass (0–20 cm layer) increased with year of release under CK but had no relationship under RN, while deep root biomass (20–200 cm layer) decreased with year of release under CK and increased under RN. The roots of modern wheat varieties responded better to soil nitrogen levels and produced higher yields, NUE and WUE than earlier varieties by adjusting root biomass distribution in soil.