Regulation effects of nitrogen application methods on wheat grain filling and corresponding physiological mechanisms

Using cultivar Shixin733（SX733） and Shimai12（SM12）, the widely planting wheat (Triticum aestivum L.) cultivars in Hebei plain, as the experimental materials, the grain filling characteristics and their corresponding mechanism regulated by nitrogen application methods were studied. Compared to those in SF (one time application N at early-jointing stage), the zeatin (Z)+zeatin riboside (ZR), volume, fresh weight and dry weight of superior-position kernels and inferior-position kernels in the tested cultivars were all increased in DF treatment (two-time application N at early-jointing stage and flag leaf expansion stage). But the inferior-position kernels increased much more than the superior-position kernels. Compared to SF, DF also increased soluble protein content, soluble sugar content and chlorophyll content of upper leaves, so were the leaf area per stem, and the ratio of leaf area per plant to grain number per spike. The 1000-grain weight and kernel weight per spike at maturity, and the yield of Shimai 12, the cultivar with high ability of drought tolerance, were all significantly higher in DF than in SF. The results indicated that nitrogen application method with DF could improve the grain filling capacity and increase wheat yield in Hebei plain. It was suggested that the increase of Z+ZR content in kernels was related to the enlargement of kernel volume and improvement of grain filling capacity in DF treatment. Therefore, the improvements of photosynthesis and population quality were important physiological bases for kernel development, especially inferior-kernels, to have relatively high kernel weight in DF. Meanwhile, nitrogen application methods in Hebei plain had different regulatory effects on photosynthesis and grain filling in the tested cultivars with different drought tolerances.