Effect of Different Form of N Fertilization on Yield Sustainability and Soil Quality in Double Cropped Rice System in a Long-Term Experiment

Purpose: Nitrogen fertilizer plays a crucial role in increasing crop yield. However, it is still unclear how long-term application of different forms of N fertilizer affect sustainable rice production and soil fertility. Methods: A ten-year field experiment was conducted to investigate the influence of four N fertilizer products on yield sustainability and soil factors in a double cropping rice system. Four types of N fertilizer were common urea with split applications (Urea), one-off application of polymer coating of sulfur-coated urea (PSCU), urea with nitrification inhibitor (UNI), and urea formaldehyde (UF). The same amount of 180 kg N ha^–1 per rice season was applied for each N fertilized treatments. Rice grain yield, a total of eighteen soil parameters, and soil quality index (SQI) were determined. Results: The UNI had significantly greater rice grain production in 4/10 years in early rice and 5/10 years in late rice, while equivalent to Urea in the other years. The UF produced 5.4% higher averaged late rice grain yield compared to Urea. The UNI had significantly higher yield stability than PSCU in early rice. In addition, the UNI resulted in significantly higher soil pH (0.3 unit), nitrate reductase activity (24.6%), exchangeable K⁺ (96.3%), and Ca²⁺(41.6%) contents than PSCU in 0–10 cm depth. A significantly higher SQI value was observed in UNI than PSCU in 0–10 cm using the minimum data set method. Conclusions: Long-term application of various N fertilizer products would have distinct influences on rice grain production and soil parameters.