Study on Optimal Nitrogen Application for Different Oat Varieties in Dryland Regions of the Loess Plateau

The present study endeavored to tackle the challenges posed by limited diversity in oat varieties and suboptimal nitrogen fertilizer utilization in the arid landscapes of the Loess Plateau. We selected three oat varieties, including early-maturing oats (E), medium-maturing oats (M), and late-maturing oats (L). In 2022, four nitrogen applications were set up as CK (0 kg N ha^-1), N1 (60 kg N ha^-1), N2 (90 kg N ha^-1), and N3 (120 kg N ha^-1). We introduced two additional nitrogen applications, N4 (180 kg N ha^-1) and N5 (240 kg N ha^-1), in 2023. The two-year study results demonstrated a significant increase in oat yield due to nitrogen application (<i>p</i> < 0.05). The highest grain yield was observed for E oats at 2216.63 kg·ha^-1 under the N3 treatment, while M and L oats had the highest grain yields at 2505.43 kg·ha^-1 and 2946.30 kg·ha^-1 under N4, respectively. The protein content of L oats reached a peak of 14.15% under N4, and the order of protein contents in oat protein components was globulin > gliadin> glutenin > albumin. The β-glucan content of L oats reached a peak of 4.92% under N3. The nitrogen fertilizer utilization efficiency (NFUE) of the three oats was highest under N2. L oats exhibited enhanced NFUE owing to an elevated pre-flowering nitrogen translocation amount (PrNTA), with a 42.94% and 29.51% increase relative to E and M oats, respectively. The pre-flowering nitrogen translocation contribution (PrNTC) in oats surpassed the post-flowering nitrogen accumulation contribution (PoNAC). Therefore, nitrogen application positively impacted oat growth, yet excessive application had an inhibitory effect. There is a significant positive correlation among oat yield, quality, nitrogen accumulation, and utilization efficiency. In summary, oat crops exhibited optimal performance in terms of yield, quality, and nitrogen use efficiency when nitrogen application rates ranged between 90 and 180 kg·ha^-1. Late-maturing oats coincide with the rainy and hot season in the northern dryland regions, making them more suitable for planting in the dryland areas of the Loess Plateau.