The study looked at how different amounts of nitrogen fertilizer and timing of application affect the growth and yield of winter wheat. They found that increasing nitrogen fertilizer led to more leaf area and photosynthesis, but reduced light penetration and certain leaf functions. Delaying nitrogen application helped maintain leaf area but had little impact on photosynthesis. Both wheat varieties had higher yields with more nitrogen, especially at 300 kg/hm2, due to larger seeds and more kernels per area. The timing of fertilizer application did not significantly affect grain yield.