Effects of Continuous Cropping and Application of Bio-organic Fertilizers on Growth, Yield and Quality of Sugar Beet under Reduced Chemical Fertilizer Application

A major problem in the cultivation of sugar beet is continuous cropping cycle. A study was carried out in the 2019–2021 season at the Agriculture and Forestry Sciences of Ulanqab, Inner Mongolia, to assess the impacts on the growth, root yield, and sugar content of sugar beet of various continuous cropping years with bio–organic fertilizers. A split plot system with three replications was set up to carry out the field testing. The main plots had five planting years, with the non-continuous of each growing season serving as the control (CK) and continuous cropping for one, two, three, and four years (designated as C1, C2, C3, and C4, respectively). The subplots had two bio-organic fertilizer levels: 6000 kg ha⁻² (Y) and 0 (N). The results demonstrated that continuous cropping stunted sugar beet growth and lowered yield and quality. The plant height, leaf area index, root volume, root yield, and sugar yield of sugar beet significantly decreased with the extension of continuous cropping years. Compared with CKN (CKY), plant height, leaf area index, root volume, and fresh weight of C1N (C1Y), C2N (C2Y), C3N (C3Y), and C4N (C4Y) all showed a significantly decreased trend. Furthermore, the plant height, leaf area index, root volume, and fresh weight reductions had amplitudes of 5.60–27.36%, 9.53–67.86%, 17.71–57.35%, and 17.54–45.03%, respectively. The distinctions between C1 and C2 were essentially not statistically significant, and the same was evident for C3 and C4. The root yield and sugar yield exhibit noteworthy relationships with each growth indices. Compared with CKN (CKY), C1N, C2N, C3N, and C4N significantly reduced their root yield and sugar yield by 19.20% and 25.08% (19.63% and 25.67%), 24.13% and 31.02% (24.74% and 32.32%), 44.03% and 55.15% (48.47% and 58.09%), and 47.89% and 61.85% (52.35% and 64.43%). Bio-organic fertilizers applied during the same planting year all had effects on the growth and yield of sugar beet; however, these effects were only significant under the planting year treatments of CK, C1, and C2. The amplitude of the increase in plant height, leaf area index, root volume, fresh weight, and root yield reached 2.76–7.95%, 10.21–24.67%, 10.66–14.88%, 7.03–14.83%, and 18.74–19.69%, respectively. Above all, sugar beet were hindered by continuous cropping, and bio-organic fertilizer can greatly increase sugar beet yield and growth for continuous cropping lasting one or two years; for continuous cropping lasting three or more years, additional measures should be considered.