One-time root-zone fertilization of controlled-release urea increases nitrogen use efficiency while reducing nitrogen loss risk in a ratoon rice field under two irrigation practices

Optimizing agronomic management plays a vital role in improving nitrogen (N) use efficiency (NUE) of rice. One-time deep application of fertilizer, especially root-zone fertilization (RZF), has already been regarded as an effective simplified fertilization method to improve rice yield and NUE. However, few studies have explored the effect of RZF on the yield and NUE in the ratoon rice system. Consequently, a 2-year field experiment was conducted, including five treatments: no N fertilizer (CK), farmers’ familiar practice (FFP), RZF of controlled-release urea (CRU) applied once into small holes with a depth of 5 cm and a distance of 5 cm away from the rice plants as basal fertilizer (RZF1); RZF of CRU applied once into small holes with a depth of 10 cm and a distance of 5 cm away from the rice plants as basal fertilizer (RZF2); and RZF of CRU applied once into small holes with depths of both 5 and 10 cm and a distance of 5 cm away from the rice plants as basal fertilizer (RZF3). The rice was planted under continuous flooding (CF) or alternate wetting and drying (AWD). The results showed that RZF2 and RZF3 increased annual yield of ratoon rice by 4.8–6.0% and 7.1–12.3% under CF, and by 5.7–7.4% and 10.9–11.0% under AWD compared with FFP, respectively. Compared with FFP, RZF2 and RZF3 significantly increased N use efficiency. The combination of RZF3 and AWD resulted in the highest water and N use efficiency.