Efficiency of calcium cyanamide on the control of tomato soil-borne disease and their impacts on the soil microbial community

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Soil-borne diseases resulting from continuous cropping are a huge problem for tomato producers around the world. In this study, differences in the efficiency of soil-borne disease control and the impact on the soil microbial community were investigated between two types of soil fumigation treatments, namely calcium cyanamide (CaCN2) and soil solarization with flooding (SS-F). Soil samples were taken at 0 days after transplantation (DAT), 60 DAT, 150 DAT and 220 DAT during the tomato season. The composition of microbiome after soil fumigation was assessed using heterotrophic plate counts, PCR and MiSeq high-throughput sequencing. CaCN2 and SS-F fumigation significantly reduced the disease incidences, at 4.98% and 11.41%, respectively, while the disease incidence of the CK was 26.62%. In addition, CaCN2 treatment significantly improved the tomato production by 21.65% compared to CK. Under CaCN2 fumigation, the soil microbial community was temporarily inhibited from 0 DAT to 60 DAT, while the bacterial and actinomycete communities recovered at 220 DAT. Remarkably, some potential beneficial microbial genera, e.g., Proteobacteria, Zygomycota phyla, Bradyrhizobium, Arthrobacter, Bacillus, Clostridium, Kaistobacter, Streptomyces, Gemmatimonadetes, and Mortierella, increased at 220 DAT after CaCN2 application. Nevertheless, the pathogenic Acremonium, Alternaria, Fusarium, Penicillium and Verticillium were significantly decreased. However, following SS-F fumigation, the relative abundance of non-soil-borne pathogenic Acremonium and Alternaria increased by 294.27% and 189.77%, respectively, compared to that in the CK. While the ratio of potential beneficial Trichoderma decreased, the bacterial composition of the SS-F soil at 220 DAT was nearly identical to that of the CK. In addition, a redundancy analysis showed that CaCN2 treatment increased the potential of hydrogen (pH) and the organic matter (OM), available phosphorus (AP), and available potassium (AK) contents, which were positively correlated with Bradyrhizobium, Rhodanobacter, Bacillus and Mycobacterium communities and negatively correlated with disease incidence. In conclusion, CaCN2 enhanced soil fertility, reduced the presence of soil pathogens, increased the relative abundance of potential beneficial bacteria and fungi and improved tomato yields.