Nitrogen application at different stages affects how wheat plants absorb and use nitrogen. The study used special methods to track nitrogen movement in two types of wheat. They found that applying nitrogen at the jointing stage led to the most nitrogen accumulation in the grains. Applying nitrogen at heading stage increased nitrogen in grains, while basal application increased nitrogen in roots. The timing of nitrogen application also affected how much nitrogen was taken up by the plants. Overall, applying nitrogen at the jointing stage is best for grain yield and protein content in wheat.