Effects of nitrogen forms on nitrogen utilization, yield, and quality of two wheat varieties with different gluten characteristics

The assimilation and utilization of different nitrogen (N) forms in wheat are different. Therefore, supplying suitable forms of N may be an effective way to optimize yield, quality, and N use efficiency (NUE) synergistically. A two-year field trial was conducted with Jimai22 (JM22) and Jimai44 (JM44) wheat varieties at differential gluten characteristics, with N form treatments: no nitrogen (N0), and nitrogen supply (225 kg ha−1) as urea (U), ammonium nitrogen (ammonium chloride, A), nitrate nitrogen (calcium nitrate, NI), U + A (1:1, UA), U + N (1:1, UN), and N + A (1:1, NA). The results showed that different N forms significantly affected wheat yield, N utilization, and grain quality. Combined application of urea and nitrate nitrogen (UN) significantly increased the spike number by 3.5% on average over U (conventional fertilization), but with no statistical difference in grain yield. N and A treatments significantly increased the activity of N metabolism enzymes in flag leaves and grains at the early filling stage but rapidly declined at the middle and late filling stages. In contrast, UN treatment significantly increased nitrate reductase and glutamine synthetase activities of wheat flag leaves and grains within 7–28 d after anthesis, which facilitated N assimilation and significantly increased free amino acids content in the middle and late filling stages, thereby significantly promoting the accumulation of gliadin and glutenin in grains, resulting in the highest protein content and the best processing quality of JM22 and JM44. Except for N0, NUE, N uptake efficiency (NUPE), and N apparent recovery fraction (NARF) under UN were the highest, which were significantly increased by 4.3%, 5.8%, and 11.8% on average compared to the U treatment, respectively. Therefore, the combined application of urea and nitrate nitrogen could synergistically improve quality and nitrogen use efficiency while maintaining yield, which is important for the rational application of nitrogen fertilizer and achieving stable yield, high quality and efficient production of wheat.