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.

The largest permafrost area in China is on the Qinghai-Tibetan Plateau (QTP), and the nitrogen biogeochemical cycles in this area have received significant attention. However, there is insufficient knowledge of the available soil nitrogen and microbial biomass nitrogen (MBN) dynamics in this region, which hinders our understanding of the changes in the ecosystem and the effects of climate change on the nitrogen dynamics in the future. In this study, we determined the monthly changes in ammonium nitrogen, nitrate nitrogen, dissolved organic nitrogen (DON), and MBN contents of the topsoil (at depths of 0-20 cm) from April 2016 to March 2017 in the permafrost region on the QTP. The results show that soil NH4+-N and DON contents decreased during the growing season, while soil NO3--N content increased during the growing season and in the middle of the winter. The soil MBN contents increased at the beginning of the growing season and decreased during peak growth period, despite significant variations among the different sites. The soil temperature was positively correlated with soil NO3--N content but it was negatively correlated with the NH4+-N and DON contents. The soil moisture was positively correlated with the soil NO3--N, DON, and MBN contents. The primary factor affecting the seasonal patterns in soil NO3--N and DON contents was soil moisture. Soil moisture and plant growth also affected soil MBN via nutrient competition. The nutrient uptake by plants overwhelmed effect of temperature on the MBN in growing season. These findings improve our understanding of the nitrogen biochemical cycles and their response to future climate change.