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 temperature 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 N 2 O and NH 3 emissions. Root-zone fertilization (RF) and controlled-release urea (CRU) show promise in decreasing the amount of emissions of N 2 O and NH 3 . 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 N 2 O and NH 3 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 positioned 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 N 2 O emissions by 55–82 % (under CF) and 52–82 % (under AWD) compared with FFP and significantly reduced the loss owing to NH 3 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 NH 4 + -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 NH 4 + -N and NO 3 - -N in field water are the main factors for N 2 O emissions and NH 3 volatilization, respectively. AWD did not reduce N 2 O emissions and NH 3 volatilization but saved water resources. Therefore, the combination of RF technology and AWD is a promising strategy to simplify the sustainable cultivation of RR. • RF of CRU reduced N 2 O emissions and NH 3 volatilization in RR. • Layered RF of CRU had highest rice yield due to reasonable NH 4 + - N distribution. • The N 2 O fluxes were related to the NO 3 -N concentrations in the 4–20 cm soil. • RF of CRU reduced NH 3 volatilization due to lower NH 4 + -N concentration.