Root-zone fertilization of controlled-release urea reduces nitrous oxide emissions and ammonia volatilization under two irrigation practices in a ratoon rice field

The ratoon rice system is one method to increase grain yield in areas where the annual accumulation of tem-perature and light resources are significantly greater than that required for single-cropping rice but insufficient for double-season rice. Rice fields are important sources of N2O and NH3 emissions. Root-zone fertilization (RF) and controlled-release urea (CRU) show promise in decreasing the amount of emissions of N2O and NH3. However, the effects of their application on rice-ratoon rice (RR) are currently poorly understood. The effect of a combination of RF and CRU on the emissions of N2O and NH3 from RR fields merits clarification. Therefore, a field experiment was conducted for 2 years. Five treatments were established with 280 kg N ha-1 (CK: no N fertilizer; FFP: urea with 5-split surface broadcasting; RF1: RF of CRU applied once into 5 cm deep holes posi-tioned 5 cm from the rice root as basal fertilizer; RF2: RF of CRU applied once into 10 cm deep holes positioned 5 cm from the rice root as basal fertilizer; and RF3: RF of CRU layered once into 5 cm and 10 cm deep holes positioned 5 cm from the rice root as basal fertilizer), and the plants were subjected to continuous flooding (CF) and alternate wetting and drying (AWD). The results showed that over a 2-year period, the RF treatments significantly reduced N2O emissions by 55-82 % (under CF) and 52-82 % (under AWD) compared with FFP and significantly reduced the loss owing to NH3 volatilization by 47-69 % (under CF) and 43-65 % (under AWD) compared with FFP. RF2 and RF3 increased the 2-year average total yield of RR by 5-10 % (under CF) and 7-11 % (under AWD). In addition, the distribution of NH4+-N in the root-zone soil of RF3 was more consistent with the rule of nutrient requirement during the long growth period of RR and had a higher ability to increase yield and stronger environmental benefits than FFP. Soil NH4+-N and NO3--N in field water are the main factors for N2O emissions and NH3 volatilization, respectively. AWD did not reduce N2O emissions and NH3 volatilization but saved water resources. Therefore, the combination of RF technology and AWD is a promising strategy to simplify the sustainable cultivation of RR.