Abstract: We explored the effects of different fertilization treatments on soil structure, nutrient characteristics, biological characteristics and yield of continuous cropping sugar beet, with the aim to screen out the best application amount of bioorganic fertilizer. With the conventional fertilization (900 kg·hm^-2 chemical fertilizer) as the control (CK), we set up bioorganic fertilizer treatments (BOF1: 1500 kg·hm^-2; BOF2: 3000 kg·hm^-2; BOF3: 4500 kg·hm^-2; BOF4: 6000 kg·hm^-2; BOF5: 7500 kg·hm^-2) on the basis of reducing 300 kg·hm^-2 chemical fertilizer. The results showed that the effects of BOF1 on soil quality indices were not significant. The BOF2 significantly increased the content of soil organic matter and available potassium. The BOF3 significantly reduced soil bulk density by 5.11%, significantly increased soil total porosity by 5.92%, soil organic matter by 14.07%, soil alkaline nitrogen by 18.35%, soil available phosphorus by 3.59%, and soil available potassium by 14.61%. Treatments BOF4 and BOF5 had similar effects on soil quality and beet yield. BOF4 and BOF5 significantly reduced soil bulk density by 9.33% and 9.65%, significantly increased soil porosity by 10.82% and 11.19%, soil organic matter by 27.22% and 27.78%, soil alkaline nitrogen by 31.62% and 35.42%, soil available phosphorus by 44.10% and 54.87%, soil available potassium by 22.93% and 30.03%, respectively. Both treatments significantly increased soil microbial biomass carbon by 22.78%-44.19% and 23.81%-60.17%, microbial biomass nitrogen by 2.45%-37.64% and 16.74%-43.56%, invertase activity by 26.03%-38.61% and 29.27%-44.71%, urease activity by 42.72%-63.20% and 51.59%-69.89%, alkaline phosphatase activity by 3.59%-33.44% and 29.60%-38.62%. There were no significant differences in each soil quality index between these two treatments. Compared with CK, the yield of BOF2, BOF3, BOF4 and BOF5 increased by 5.69%, 11.82%, 22.29%, and 11.95%, respectively. The beet yield of treatment BOF4 was significantly higher than that of BOF2, BOF3, and BOF5. Treatment BOF4 increased the economic benefits of continuous cropping sugar beet by 12.79%. In all, the application of 6000 kg·hm^-2 bioorganic fertilizer can achieve the synergetic improvement of soil quality, yield and economic benefits of continuous cropping sugar beet.

Key words: reduction of chemical fertilizer, bioorganic fertilizer, continuous cropping sugar beet, soil quality, yield, economic benefit