Wheat Nitrogen Use and Grain Protein Characteristics Under No-Tillage: A Greater Response to Drip Fertigation Compared to Intensive Tillage

No-tillage (NT) has been widely recognized for significantly enhancing crop yield and nitrogen (N) use efficiency in dryland agricultural systems globally. However, in irrigated fields, NT has demonstrated adverse effects on wheat yield, and limited information is available regarding its impact on N uptake and use efficiencies, and grain protein characteristics. Previous studies concluded that drip fertigation (DF) achieved superior yield gain over the conventional N fertilizer broadcasting with flood irrigation (BF) under NT compared to rotary tillage (RT) and intensive tillage (PRT; first plowing followed by rotary tillage). This study measured tissue N concentration, grain protein content and composition, dough processing quality traits, and the activities of N metabolism enzymes in flag leaves and developing grains. The objectives were to (1) evaluate the response of N use traits and grain quality to DF, and (2) elucidate the relationship between gains in yield and N uptake across varying tillage methods. Results revealed that DF significantly increased N uptake by 35.4–38.0%, 22.1–22.2%, and 16.0–16.6% over BF under NT, RT, and PRT, respectively. This boosted N uptake predominantly contributed to enhanced N use efficiency (grain production per unit of total soil mineral and fertilizer N input). Regression analysis indicated that increased N pre-anthesis uptake was the primary driver of yield improvement by DF (r2 > 0.99, P < 0.01). Furthermore, NT demonstrated superior improvements by DF in N nutrition index, grain protein content, gliadin content, wet gluten content, and water absorption rate compared to RT and PRT. In conclusion, wheat N use and grain protein under NT responded greater to DF than intensive tillage. Therefore, our findings emphasize that transitioning from conventional water and N management to DF is an effective and practical strategy for enhancing N uptake, achieving high yield, improving N use efficiency, and enriching grain protein content, particularly under NT conditions.