Unravelling the Mechanisms of Improving Wheat Growth, Yield, and Grain Quality Under Long-Term Corn Straw Return plus N Fertilizer Mode

In modern agricultural production, straw return (SR) plus nitrogen (N) fertilizer (SR-N) input has been considered a better practical mode to improve soil fertility and crop yield. Here, we investigate the underlying mechanisms of long-term SR-N application on wheat growth, yield, and quality. Wheat seeds were cultivated in 11-year-old plots treated with different N fertilizer levels under corn SR and non-straw return (NSR) conditions. Five levels of N fertilizer were set: N0 (0), N1 (90 kg ha(-1)), N2 (180 kg ha(-1)), N3 (270 kg ha(-1)), and N4 (360 kg ha(-1)). The wheat plants in SR-N2 exhibited the best growth status, the highest yield, and yield components. Physiological indicators exhibited that wheat plants in SR-N2 also had the maximum chlorophyll, soluble sugars, and protein contents, the highest antioxidant enzyme activities, and the lowest malondialdehyde (MDA) content. Wheat grains in SR-N2 had the highest protein content, which might be attributed to the highest glutamine synthetase activity during filling stage. qRT-PCR analysis showed that six genes related to N uptake and assimilation were significantly upregulated in SR-N2 treatment. Taken together, SR-N2 might be the effective mode that decrease the N fertilizer usage but maintain the maximize crop yield and grain quality by reducing oxidative stress and upregulating the expression of N metabolism-related genes.