Effects of continuous cropping and application of bio-organic fertilizer on photosynthetic performance, dry matter accumulation and distribution of sugar beet.

One of the major problem in the cultivation of sugar beets is continuous cropping obstacle in China. In order to evaluate the effects of continuous cropping year on the photosynthetic performance, dry matter accumulation, and distribution of sugar beet, this study was conducted in the 2020-2021 crop season at the Agriculture and Forestry Sciences of Ulanqab, Inner Mongolia. A split plot system arrangement with three replications was set up to carry out the field testing. The main plots had five planting years, with the a first cropping of each growing season serving as the control (CK) and four continuous cropping treatments for one, two, three, and four years (designated as C1, C2, C3, and C4, respectively). The subplot consisted of two fertilization treatments designated as 0 kg ha bio-organic fertilization (N) and 6000 kg ha bio-organic fertilization (Y). The findings demonstrated that the continuous cropping impeded sugar beet photosynthesis as well as the accumulation and dispersion of the dry matter in leaf, petiole, and root. The intercellular CO concentration (Ci), transpiration rate (Tr), stomatal conductance (Gs), net photosynthetic rate (Pn), and SPAD value were dramatically dropped as the number of continuous cropping years increased under the crop. Compared with CK, the SPAD value, Pn, Ci, Tr, Gs of continuous cropping treatments were significantly reduced by an average of 10.09-48.21%, 14.60-43.19%, 12.00-42.86%, 7.77-43.83%, 9.61-37.68%, respectively. The dry matter accumulation of leaf, petiole, root, and the whole plant were also reduced by 11.86-49.61%, 9.58-44.77%, 17.26-53.76%, and 10.62-49.79%, respectively. With the increasing of continuous cropping year, the growth of sugar beet was significantly inhibited. Study revealed that continuous cropping had an impact on the distribution of dry matter accumulation of sugar beet; it considerably raised the dry matter ratio above ground, lowered the dry matter ratio below ground, and prevented dry matter from moving from aboveground towards root, whitch caused a decline in sugar beet root production and disturbed the root shoot ratio. Compared with CK, the root shoot ratio significantly decreased by 3.62-19.76%. Under continuous cropping stystem, the application of bio-organic fertilizer had an effect on promoting the photosynthesis of sugar beet, and regulating the distribution and transport of dry matter. The effects of bio-organic fertilizer were significantly under continuous cropping for 1-2 years. Compared with C1N and C2N, the Pn, Ci, Tr, Gs of C1Y and C2Y were significantly increased by 12.79-22.50%, 14.76-16.47%, 4.76-13.08%, 8.51-12.70%, and 13.69-18.91%, 12.17-14.60%, 5.71-15.14%, 7.58-15.41%, respectively. Dry matter accumulation of leaf, petiole, root, whole plant were significantly increased by 8.32-16.18%, 10.80-13.33%, 14.93-20.13%, 14.12-15.43%, and 10.65-15.32%, 6.58-15.63%, 15.37-20.94%, 12.68-16.85%, respectively. Nonetheless, the root shoot ratio increased by 4.58-8.56% and 4.52-7.35%. Above all, Under continuous cropping conditions, the application of 6000 kg ha bio-organic fertilizer could effectively promote the photosynthesis of sugar beet, and better regulate the distribution and transport of dry matter of sugar beet. These results can provide scientific basis for bio-organic fertilizer to alleviate the problem of sugar beet continuous cropping.