Effects of an Organic Amendment on Cassava Growth and Rhizosphere Microbial Diversity

This study aimed to determine the effects of different dosages of an organic amendment, consisting of a Chinese herbal compound, on cassava growth and rhizosphere microbial diversity. In this study, cassava SC8 growth was determined under four treatments. The growth was promoted with the application of an organic herbal compound amendment, biochar powder, and an agent, in the following groups: 900 kg/ha of organic amendment powder (topdressing) + agent (T1); 1200 kg/ha of organic amendment powder (topdressing) + agent (T2); 1500 kg/ha of organic amendment powder (topdressing) + agent (T3); and an unfertilized control (T4). After 240 days of treatment, the height, the diameter of the stem, the maximum perimeter of the cassava, the tuber number, the weight of a single tuber, the yield per hectare, the mineral elements in the cassava plant, the ash content in the starch and the microbial diversity in the soil were measured. Compared with the control group, the application of 1200 kg of the Chinese herbal compound amendment per ha (T2) had the strongest positive effect on cassava growth, while the height, diameter of the stem and yield per hectare all showed increases of 24.22%, 18.82% and 35.71%, respectively. As for the dry matter content of the tubers, that of T2 decreased by 5.96% compared with T4, while no substantial difference existed among the other groups. The Fe content in T2 decreased by 29.46%, and the Zn in T3 increased by 39.48%, while the contents of other metal ions in the four treatment groups showed no substantial difference. At the same time, the experiment also revealed that, in terms of the bacterial abundance in the soil, Streptophyta dominated in T2, and Fimbriimonas was the unique genera of T2. In addition, the abundances of Nocardioides and unclassfied_Spartobacteria in the T2 group were greatly considerable compared to the other treatment groups. In terms of the fungal abundance in the soil, after being treated with different concentrations, the composition of the soil’s fungi differed greatly among the groups, and the samples at different concentrations contained more than 20 species of unique bacteria. At the genus level, compared with the control group, the relative abundance of unclassfied_Chaetomiaceae in the treatment groups was considerably reduced, and the relative abundance of Psathyrella in T1 increased substantially. The results indicated that the organic amendment could improve the growth of cassava, as well as help to enhance the diversity and optimize the composition of the rhizosphere microbiome.