Increase in yield and nitrogen use efficiency of double rice with long-term application of controlled-release urea

Controlled-release urea (CRU) has better characteristics than conventional urea for synchronizing nitrogen (N) release with plant uptake. Understanding the effects of CRU on crop yield and N use efficiency (NUE) has long been the key to evaluate the performance of CRU. A long-term experiment over five consecutive years was conducted in Changsha, Hunan Province, China, to investigate the effects of polyethylene-coated urea with a 90-d release period on the yield and NUE of double rice (early and late crops are grown in the same year), the amount of residual soil mineral N and the soil–plant N balance, as well as on the economic benefits. Four N fertilizer treatments including CK (no N fertilizer), U (conventional urea), CRU1 (polyethylene-coated urea with equal N application rate to U) and CRU2 (20% reduction in N application rate of CRU1) were established. The results indicated that CRU1 application increased the yield and NUE of double rice by 11.0 and 13.5%, respectively, compared with U. Higher yield and NUE of late rice were found than in early rice in CRU treatments. Compared with conventional U, the yield and NUE of early rice in the CRU1 treatment were increased by 6.0 and 10.2%, respectively, and those of late rice were increased by 15.4 and 13.8%, respectively. There was no significant difference between CRU1 and CRU2 in double rice yield. Furthermore, CRU treatments (including CRU1 and CRU2) had higher apparent residual Nmin rate (ARNR) and apparent N recovery rate (ANRR), but lower apparent N loss (NS) than the conventional U treatment. Concentrations of NH4+-N and NO3–-N were greater in the surface soil (0–20 cm) and lower in the deeper soil layer (40–60 cm) with CRU treatments than in the U treatment after harvest. Moreover, CRU application produced a greater economic benefit than conventional U application. In general, CRU outperformed U fertilizer in terms of rice yield, NUE, soil–plant N balance, economic benefit, and CRU2 provided greater comprehensive benefits than CRU1. It is suggested that CRU application is beneficial for solving N management challenges in the production of rice.