Controlled-release nitrogen fertilizer combination strategies regulate carbon and nitrogen metabolic processes to improve soft wheat quality

The objective of this study was to identify the suitable blended controlled-release nitrogen (N) fertilizer strategies (BCRNFs) for soft wheat production and to elucidate its underlying physiological mechanisms. A two-year field experiment conducted at two sites using two N application rates and three N fertilizer types. In each N rate, the N fertilizer types include: CK, common urea applied twice; BCRNF1, which featured a single basal application of a 3:2 blend of 60-d and 180-d controlled-release N fertilizers, aiming to delay N release until later growth stages; BCRNF2, which featured a single basal application of 3:4:3 blend of urea, 60-d, and 180-d controlled-release N fertilizer, aiming to release N from early to middle growth stages. Compared with CK, BCRNF2 promoted starch synthesis and sucrose supply during the late grain-filling period of soft wheat, thereby increasing starch and amylose contents as well as the amylose-to-amylopectin ratio, while diluting protein and its component contents. The changes in these parameters mediated by BCRNF2 directly increased peak viscosity, trough viscosity, breakdown viscosity, final viscosity, and setback viscosity, ultimately improving soft wheat quality. BCRNF1 under reduced N application enhanced sucrose transport and starch synthesis capacity during the late growth period, which similarly supported the increase in starch content, the decrease in protein content, and the improvement of some key pasting characteristics. Therefore, BCRNF1 under reduced N conditions and BCRNF2 under conventional N conditions can enhance final grain quality and processing quality by increasing carbon metabolism during soft wheat grain filling, making them suitable for soft wheat production.