Grain yield, plant nitrogen content and nitrogen use efficiency as affected by controlled-release urea and straw biochar in a rice field

Resulting from the positive effect on rice productivity, the application of biochar and controlled-release urea in the form of polymer-coated urea (PCU) in crop production attracts more and more interest. However, field studies considering the combined effect of biochar and PCU are rare. This 2-year study examined the combined effects of biochar and PCU on yield, yield components, plant height, plant nitrogen concentration and nitrogen recovery efficiency in a waterlogged rice field. Experimental treatments combined two biochar rates (0 and 2800 kg ha−1) and three nitrogen rates (0, 120 and 180 kg N ha−1). The results showed a yield decrease under biochar application without nitrogen fertilizer. The application of 120 kg N ha−1 PCU and biochar had the highest yield in 2017. No significant differences of grain yields were indicated between 120 and 180 kg N ha−1. High grain yield and nitrogen use efficiency was obtained with 120 kg N ha−1 PCU. Therefore, 120 kg N ha−1 PCU can be recommended for rice production in this area.