LAUSR

Abstract Controlled release urea (CRU) and urea with nitrification inhibitor could improve yields and nitrogen use efficiency (NUE) in a number of production systems. However, their effectiveness will be strongly influenced by environmental conditions. The objective of this research was to evaluate the effects of CRU and urea with nitrification inhibitors on grain yield and nitrogen use efficiency under different rice cropping systems. A five-year experiment on double rice cropping systems and a two-year experiment on single rice cropping systems were conducted using four treatments: not N fertilized (CK), prilled urea with split applications (PU), single basal application of polymer coating of sulfur-coated urea (PSCU) and prilled urea with the nitrification inhibitor 2-chloro, 6-(trichloromethyl) pyridine (NPU). The fertilizers were applied at the rate of 180 kg N ha −1 under a subtropical monsoon climate in China. The results suggest that NPU significantly increased the five-year average grain yield and NUE when compared with the PU treatment by 9.7% and 10.3% for early rice, and 9.6% and 8.8% for late rice, respectively. However, PU treatment produced a similar two-year average rice grain yield and 3.1% higher NUE when compared with the NPU treatments for single rice. PSCU treatment significantly increased average grain yield by 5% and 3.7% compared to the PU treatment of late rice and single rice, respectively. In addition, PSCU treatment resulted in the highest total N uptake and NUE during 2012–2015 for late rice and 2014–2015 for single rice, indicating synchronized N release in accordance with the N requirement of rice. However, the use of PSCU was not effective in improving grain yield or NUE of early rice owing to the delayed release of N during the tillering-heading stage. Overall, our results suggest that urea with nitrification inhibitor is preferable to urea for double rice cropping systems, and that PSCU is more suitable for single rice.