Effect of Nitrogen Application on Root and Yield Traits of Chinese Spring Wheat (Triticum aestivum L.) under Drip Irrigation

To clarify the regulatory effects of different N fertilizer treatments on the root morphology, physiological characteristics, and assimilate accumulation of drip-irrigated spring wheat under the northern border climate, we used strong wheat Xinchun 38 (cv. XC 38) and medium gluten wheat Xinchun 49 (cv. XC 49) as test materials in 2019 and 2020, and cultivated them in soil columns at Nck (300 kg·ha−1), A1 (240 kg·ha−1), A2 (210 kg·ha−1), and N0 (0 kg·ha−1). We also studied the effects of N application on root morphological characteristics, key enzymes of N metabolism, antioxidant enzymes, dry matter accumulation distribution, and yield of drip-irrigated wheat. The results showed that the root morphological characteristics, key enzymes of nitrogen metabolism, antioxidant enzymes, shoot dry matter accumulation, spike dry matter, and yield all showed an increasing and then decreasing trend with increasing nitrogen application. Among them, A1 treatment showed the best root length density (RLD), root volume density (RVD), root mass density (RMD), nitrate reductase (NR), glutamine synthetase (GS), glutamate synthetase (GOGAT), glutamic-pyruvic transaminase (GPT), superoxide dismutase (SOD), peroxidase (POD), root activity, shoot dry matter accumulation, spike dry matter, and yield, which were significantly higher than other treatments. The malondialdehyde (MDA) content decreased by 3.36–15.70% compared with other treatments. Correlation analysis showed that yields were positively correlated with RLD, RVD, RMD, GS, and GPT and negatively correlated with MDA. Nitrogen treatments and varietal intercropping had significant effects on RLD, root activity, NR, GS, GPT, POD, and yield. Therefore, moderate N reduction (240 kg·ha−1) under the drip irrigation pattern in Xinjiang can improve the morphological characteristics and physiological functions of wheat roots, promote the distribution and transport of dry matter to spikes, and facilitate yield formation.