Polyolefin‐Coated Urea Decreases Ammonia Volatilization in a Double Rice System of Southern China

Field evaluations of slow‐release N fertilizers are needed to improve N use efficiency while reducing NH 3 volatilization. Ammonia volatilization losses, floodwater NH 4 + , and aboveground rice ( Oryza sativa L.) tissue N accumulation were compared between non‐coated urea (NCU) and polyolefin‐coated urea (POCU) applications in a double‐rice production system of subtropical China. A factorial treatment design included two urea sources such as POCU and NCU applied at 75 and 150 kg N ha −1 , and a no‐N control. For early and late rice seasons, floodwater NH 4 + and pH increased significantly within 7 to 10 d after NCU applications and then decreased rapidly. Nitrogen losses through NH 3 volatilization accounted for 16 to 30% and 4 to 8% of the total N applied for NCU and POCU, respectively. Applications of POCU significantly increased N accumulation in aboveground rice biomass due to a slower N release and better synchrony between in‐season rice N demand and N supply from this fertilizer. Applications of POCU at a rate of 75 kg N ha −1 provided the optimal amounts of N for early and late rice crops and reduced NH 3 volatilization losses. The use of slow release urea fertilizers should increase N use efficiency and maintain the high grain yield in the double rice production systems of subtropical China.