Appropriate amount of controlled-release fertilizer for aerial-sown rapeseed at paddy and upland field

To clarify the suitable application rate of controlled-release fertilizer for aerial-sown rapeseed, so to achieve the goal of improving the yield potential and reducing the productive cost for rapeseed production, in this study a field experiment was conducted in paddy and upland area with both six fertilization treatments, which included controlled-release formulated fertilizer quantities of 0, 300, 600, 900 and 1200 kg/hm² (CRF0, CRF300, CRF600, CRF900 and CRF1200) as well as the use of conventional fertilization (CF). The response of yield formation, nitrogen uptake accumulation and the changes of soil mineral nitrogen concentration for aerial-sown rapeseed during the growth season were investigated as affected by different amount of controlled-release fertilizer application in field experiment. The results were showed as followed: the yield of aerial-sown rapeseed at maturity in paddy field was overall lower than that in upland field, particularly for the low amount of fertilization treatment. The average of nitrate-nitrogen concentration in the soil during the growth season of paddy field was 84.4% lower than that in upland field, and the ratio of nitrate to ammonium was reduced by 93.4% as well. The rapeseed yield in paddy field were significantly improved with the increase amount of controlled-release fertilizer. Compared with CF, CRF1200 significantly increased the yield of aerial-sown rapeseed by 32.4% (P<0.05), the pod number per plant and harvest density of rapeseed at maturity were significantly increased by 33.7% and 70.5% (P<0.05), respectively, the accumulation of aboveground biomass was significantly increased by 45.0%-98.2% (P<0.05), and the crop growth rate from sowing-budding stage were significantly increased by 84.5%-106.8% (P<0.05). Compared to CF, with the quantities of 900 kg/hm² or less of controlled-release fertilizer, the pod number of rapeseed were all significantly decreased by 27.6%-63.2% (P<0.05), and the accumulation of aboveground biomass, the amount of nitrogen uptake and crop growth rate were all severely inhibited for the treatment of CRF300 and CRF600 (P<0.05), the crop growth rate was decreased significantly by 54.7% from pod to maturity of CRF900 (P<0.05). Whereas with the increase of controlled-release fertilizer, the yield of aerial-sown rapeseed in upland field increased firstly and then decreased. Compared with CF, CRF900 significantly increased the rapeseed yield by 24.7% (P<0.05), mainly due to the remarkable improvement of the crop growth rate from sowing-seedling stage by 25.0% and from pod-maturity stage by 3.75 times, respectively (P<0.05). Compared with CRF900, CRF300 and CRF600 significantly decreased the crop growth rate by 74.6% from seedling to budding stage, the crop growth rate of CRF1200 were significantly lower by 39.5% from pod to maturity (P<0.05). In conclusion, in this research, the yield of aerial-sown rapeseed showed different between paddy field and dry field at the same quantities of fertilization application. The special controlled-release fertilizer of 900 kg/hm² in upland areas of aerial-sown rapeseed can effectively coordinate the soil nitrogen supply and plant nitrogen uptake during the early and late growth stages of plant, so as to obtain the sufficient and effective number of pods and plant density of rapeseed at maturity. Moreover, in paddy field, the application of 1200 kg/hm² controlled-release fertilizer can promote the nitrogen and dry matter accumulation of rapeseed before wintering, ultimately increase the effective number of pods and achieve higher yield.