Objectives Effects of controlled-release nitrogen fertilizers (CRU) on crop yield, total nitrogen accumulation, economic benefit and the residual effects of CRU applied in previous crop season were studied under rice–rapeseed and rapeseed–rice rotation periods.
Methods Field experiments were conducted in paddy-upland rotation areas of Anhui Province under rice–rapeseed rotation systems in the period of 2014–2015. Three treatments were set up: 1) No nitrogen (N0); 2) conventional nitrogen fertilizer by split application (PU); and 3) single basal application of 100% controlled-release nitrogen fertilizer (CRU). For the rice–rapeseed rotation period, N0, PU and CRU were included in the previous crop. For the later crop the original two nitrogen application treatments in the previous crop were split into with and without N application sub-treatments, and the nitrogen treatments kept consistent with the previous crop. Crop yield, total nitrogen accumulation, nitrogen use efficiency, economic benefit and the residual effects of CRU applied in previous crop were analyzed in the treatments under the rice–rapeseed rotation system and the rapeseed–rice rotation system. The optimum application period of CRU under rice–rapeseed system was defined.
Results Due to different N fertilizer forms and rotation periods, the differences among the yields, N uptakes, N use efficiencies and economic benefit were significant. Compared with PU, the annual yield, N uptake, N use efficiency (NRE), N contribute efficiency (NCE), agronomic efficiency of nitrogen (NAE), partial factor productivity of nitrogen (NPFP) and net income (NI) in CRU were increased by 8.0%, 31.0%, 17.2 percentage points, 5.8 percentage points, 2.7 kg/kg, 2.6 kg/kg, 12.8% and 5.9%, 23.5%, 19.1 percentage points, 4.9 percentage points, 3.3 kg/kg, 3.3 kg/kg and 10.9% under the rice–rapeseed rotation period with and without N application for the later crop, respectively, while those were 15.6%, 34.9%, 21.8 percentage points, 11.5 percentage points, 4.4 kg/kg, 4.5 kg/kg, 17.1% and 6.8%, 22.2%, 25.9 percentage points, 6.0 percentage points, 4.2 kg/kg, 3.8 kg/kg and 11.1% under the rapeseed–rice rotation period with and without N application for the later crop, respectively. The recovery N efficiency, residual N efficiency and accumulative N efficiency in the CRU treatments were 36.1%, 11.6%, 47.7% and 29.3%, 14.1%, 43.4% in rice and rapeseed seasons, respectively, which were significantly higher than those in PU. The recovery N efficiency and accumulative N efficiency in CRU in rice season were higher than those in rapeseed season.
Conclusions Application of CRU would achieve high crop yields and N efficiencies and economic benefit under rice–rapeseed rotation systems, and the application effect of CRU in the rice season was superior to that in the rapeseed season. It was suggested that the controlled-release nitrogen fertilizer should be applied to the rice–rapeseed rotation period.
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