To scientifically evaluate the effects of three environmentally friendly fumigants, dazomet, metham sodium, and calcium cyanamide, on soil microbial community changes, soil from a greenhouse with 7 years of continuous cropping was studied. Soil samples were collected from unfumigated soil (CK), dazomet-fumigated soil (DZ1), metham sodium-fumigated soil (MS1), calcium cyanamide-fumigated soil (CC1) at seedling recovery stage, dazomet-fumigated soil (DZ2), metham sodium-fumigated soil (MS2), and calcium cyanamide-fumigated soil (CC2) at fruiting stage. The effects of different fumigant treatments and treatment periods on soil microbial community changes, tomato yield, and soil-borne diseases were analyzed. The results showed that the application of soil fumigants significantly reduced the richness and diversity of soil bacterial and fungal communities at the seedling recovery stage. Three months after transplanting (at the fruiting stage), the soil microbial diversity gradually recovered. After fumigation, the relative abundance of soil bacteria and fungi at the phylum level changed. Under different fumigation treatments, the trends in the relative abundance changes of species during the seedling recovery and fruiting stages after fumigation exhibited certain differences. Analysis of the dominant soil microbial communities at the genus level revealed that fumigation effectively eliminated pathogenic genera such as Fusarium, but the inhibition rate of pathogens increased during the seedling recovery stage after fumigation. By comprehensively considering microbial community changes during the seedling recovery and fruiting stages after fumigation, as well as indicators such as yield, incidence of soil-borne diseases, and disease index, among the three fumigation treatments, the DZ treatment demonstrated the best overall performance. It increased beneficial genera while reducing the majority of pathogenic genera in the soil. Even after three months, when the plants transitioned from the seedling recovery stage to the fruiting stage, the relative abundance of harmful genera remained suppressed, and the abundance of some beneficial genera increased. However, given the broad-spectrum microbial eradication by fumigants and the time-limited suppression of pathogenic communities, it is essential to supplement beneficial microorganisms promptly after soil fumigation, such as by applying microbial fertilizers in combination.

To study the effects of dazomet, which is a soil fumigant and microbial inoculant (Trichoderma harzianum) on the bacterial and fungal diversity of continuously cropped strawberry soil, this work aimed to provide a theoretical basis for the treatment of continuously cropped strawberry. The soil of a strawberry greenhouse with continuous cropping for 10 years was used as the research object, and rhizosphere soil samples from strawberry continuous cropping were collected before dazomet fumigation (M0), after dazomet fumigation (M1), after dazomet fumigation in the fruit early phase without the addition of T. harzianum (H0), and after the addition of T. harzianum (H1). The diversity of soil bacteria and fungi was detected via the Illumina HiSeq high-throughput sequencing platform. The results revealed that the richness and diversity of the soil bacterial and fungal communities decreased after dazomet fumigation and that the addition of T. harzianum after dazomet fumigation increased both the richness of the soil bacterial communities and the diversity of the fungal communities. At the genus level, the composition ratios of the soil bacterial and fungal communities in the different treatments also substantially differed. The bacterial community compositions of H0 and H1 were the most similar, while the fungal community compositions of M0 and H0 were the most similar. The analysis of beneficial and harmful dominant genera in the soil revealed that dazomet fumigation could kill pathogenic fungi such as Ilyonectria and Fusarium in the soil and reduce beneficial bacteria and fungi such as Streptomyces, Flavobacterium, Mortierella, and Talaromyces. The addition of T. harzianum to dazomet fumigation can increase the abundance of beneficial bacteria and fungi such as Bacillus, Flavobacterium, and Cladorrhinum in the soil as well as reduce the abundance of pathogenic fungi such as Monilinia, Ilyonectria, and Fusarium. In summary, the use of dazomet fumigation combined with microbial inoculation changed the microbial structure of continuously cropped soil, increased the abundance of beneficial bacteria and fungi, and reduced the abundance of the vast majority of pathogenic fungi in the soil. Therefore, dazomet fumigation combined with microbial inoculation is an effective method for overcoming obstacles to continuous cropping of the strawberry.

To scientifically assess the effects of environmentally friendly fumigants on soil microbial communities, soils from a 7-year continuous cropping tomato greenhouse were studied, with unfumigated soil used as the control (CK). Rhizosphere soil samples treated with dazomet (DZ), metam sodium (MS) and calcium cyanamide (CC) were collected at the seedling recovery and fruiting stages. The influences of different fumigants and growth stages on soil microbial communities, tomato yield and soil-borne diseases were investigated. The results indicated that soil fumigation significantly decreased microbial community richness and diversity at the seedling recovery stage, which gradually recovered at the fruiting stage. The variation trends of microbial relative abundance at the phylum and genus levels differed among the treatments at both stages. At the phylum level, Actinobacteria and Proteobacteria were the dominant bacterial phyla, and Ascomycota was the dominant fungal phylum. Genus-level clustering revealed that the bacterial communities under MS and CC were similar to those under CK at the fruiting stage, whereas the fungal communities under all the fumigation treatments were significantly distinct from those under CK. Fumigation effectively inhibited pathogenic genera, including Amesia, Fusarium, Rhizopus and Ascobolus, at the seedling recovery stage, but some pathogens recovered at the fruiting stage. The relative abundance of Fusarium in the MS treatment increased to 8.25%. DZ treatment performed optimally: it increased beneficial genera such as Bacillus and Streptomyces at the seedling recovery stage, suppressed harmful genera, including Amesia and Fusarium, and further enriched Remersonia at the fruiting stage. Fumigation significantly improved tomato yield and reduced the incidence of soil-borne diseases. The yield of CC was the highest, at 35.41% greater than that of CK, but it was not significantly different from that of DZ in terms of cost. In conclusion, the DZ treatment had the best overall effect.

To study the effects of different microbial agents on the microbial community structure of continuously cropped strawberry soil after soil fumigation, seven treatments were applied: T1 (Trichoderma harzianum + Bacillus subtilis + actinomycetes), T2 (Trichoderma harzianum + Bacillus subtilis), T3 (Trichoderma harzianum + actinomycetes), T4 (CK) (water control), T5 (Bacillus subtilis), T6 (actinomycetes) and T7 (Trichoderma harzianum). A high-throughput sequencing platform (Illumina HiSeq 2500) was used to analyze the soil bacterial and fungal communities and their compositions. Compared with the T4 (CK) treatment, the application of microbial agents increased the richness and diversity of soil bacteria and fungi, and the effects of single microbial agents and compound microbial agents differed. The richness, diversity indices and population sizes of bacteria and fungi in the T6 treatment were the highest. The Chao1, observed species and Shannon indices of bacteria were 22.51%, 23.56% and 5.61% greater, respectively, than those of T4 (CK). The Chao1, observed species, Shannon and Simpson indices of fungi were 41.28%, 41.83%, 128.02% and 88.65% higher, respectively, than those of T4 (CK). At the genus level, the bacterial community compositions of T2 and T6 were the most similar, and the fungal community compositions of T1 and T5 were the most similar. Analysis of the genera in the dominant communities revealed that the application of microbial agents after dazomet fumigation increased the numbers and recovery rates of soil bacteria and fungi, especially the beneficial fungal genera, Lecanicillium, Cladosporium, Saccharomyces and Aspergillus. An investigation of strawberry growth and yield-related indicators revealed that the T6 treatment resulted in the lowest seedling mortality and the highest yield. In summary, adding microbial agents to soil with continuous cropping of strawberry after fumigation with dazomet is a scientifically sound and effective method for reconstructing the balance of the soil microbial flora and overcoming the obstacles associated with continuous cropping. In this study, the T6 (actinomycetes) treatment presented the best performance.