Mechanized transplanting with side deep fertilization boosts rice yield and nitrogen use efficiency in Eastern China. By applying nitrogen fertilizer deep in the soil during mechanical rice transplanting, researchers found increased grain yield and profitability. The method improved nitrogen uptake, nitrogen use efficiency, and economic returns for two rice cultivars. Compared to manually applied fertilizer, mechanically applied fertilizer led to higher grain yield and nitrogen use efficiency. The side deep application of nitrogen fertilizer increased N recovery efficiency and agronomy efficiency, resulting in improved grain yield. The controlled-release urea treatments showed the highest benefit-cost ratio due to increased returns and reduced fertilization costs. Overall, mechanized side deep fertilization can enhance the efficiency and profitability of rice production.