Optimizing seed rate improves soft wheat quality, economic returns, and apparent nitrogen recovery with lower nitrogen inputs

Abstract

Grain protein content (GPC) often increases with nitrogen (N) fertilizer; however, low GPC is preferred for soft wheat (Triticum aestivum L.). The combined effects of decreasing N and increasing seed rate (SR) on soft wheat quality, economic benefits (Eb), apparent N recovery (ARN), and soil nitrate-N residual (SNR) are poorly understood. Field experiments were conducted with three SRs (SR₁₃₅, SR₁₈₀, and SR₂₂₅) and two N levels (N₂₃₅ and N₂₉₀) in 2017–2018, and three N levels (N₂₉₀, N₂₃₅, and N₁₈₀) with a control (N₀) in 2018–19. The results showed that storage proteins, GMP, HMW-GS, and Zeleny sedimentation value significantly decreased with lower N levels and increased with higher SR. At the same SR, the significant difference for the parameters mentioned were greater at a low N rate than at a high rate. Furthermore, grain yield (GY), Eb, ARN, and SNR were significantly affected by N and SR. Increasing SR from 135 to 180 resulted in an average Eb increase of 13.32%, while increasing from 180 to 225 led to a decline of 3.75%. Compared to N₂₉₀, N₂₃₅ decreased SNR and GPC by 27.5% and 4.7%, respectively, but increased ARN by 18.3%. The highest Eb (13,914 CNY) and ARN value (57.5%) were observed with the treatment (N₂₃₅SR₁₈₀). Additionally, optimal combination for maximizing GY (90%), Eb (87.8%), and ARN (97%) was found at N₂₃₅SR₁₉₈, according to regression and spatial analysis. This study confirmed that optimizing N and SR can improve soft wheat quality and resource use efficiency without decreasing yield.