Subsoiling Sustains Winter Wheat Yield with Reduced Nitrogen Input in the North China Plain

Excessive nitrogen (N) input and repeated shallow tillage constrain sustainable winter wheat production in the North China Plain. A two-year field experiment was conducted to compare rotary tillage, subsoiling, and no-tillage under N application rates of 120, 180, and 240 kg ha−1. Subsoiling generally increased grain yield, with yields under subsoiling at 180 kg N ha−1 (SN180) reaching 8129.64 and 7700.89 kg ha−1 in the two growing seasons, respectively, without significant differences from SN240, while reducing N input by 60 kg ha−1. SN180 favored post-anthesis dry matter accumulation and post-anthesis N uptake. Accordingly, it achieved partial factor productivity of applied N of 45.16 and 42.78 kg kg−1, and N uptake efficiencies ranging from 1.29 to 1.46 kg kg−1, which were higher than those under SN240 and other tillage practices at the same N rate. In 2023–2024, SN180 increased root length density at 20–40 cm by 41.8% and 59.7% and root dry weight density by 22.0% and 20.5% compared with rotary tillage and no-tillage, respectively. SN180 also maintained relatively high nitrate reductase and glutamine synthetase activities during the same growing season, although the responses varied among plant organs and growth stages. Under the conditions of this two-year field experiment, subsoiling combined with 180 kg N ha−1 achieved the most favorable balance between grain yield and N use performance among the treatments tested, indicating its potential as a management option for irrigated winter wheat production in the North China Plain.