Objectives  Continuous cropping obstacle-induced soil quality degradation inhibits the sustainable development of crop production. Vermicompost application has been proved to be an effective way to improve the quality of soils with continuous cropping obstacle. This research compared the efficiencies of in-situ and ex-situ vermicomposting in overcoming the obstacles in tomato production, in order to optimize its efficacy for sustainable crop production.

  Methods  A field experiment was conducted for three years in a greenhouse where tomato had been continuously grown for 5 years. Urea application at 0.69 t/hm² was used as the control (CK), while vermicompost application at 130.4 t/hm² (T1) and in-situ vermicomposting comprising of 179.4 t/hm² cow dung plus 1.76 t/hm² earthworm (T2) were setup as treatments. At the beginning of each cropping season (CS), the urea and vermicompost were applied, but earthworm was only used at the first CS. Soils were sampled at harvest period to measure physiochemical properties, microbial diversity and metabolic functions.

  Results  1) Both vermicomposting treatments (T1 and T2) showed significantly lower soil pH and EC as compared to CK. The T2 treatment had significantly lower soil EC in the first two CSs and did not show significant difference in the third CS as compared to the T1 treamtment. In all three CSs, soil total N, P, K and C, and available N and K exhibited a trend of T2>T1>CK (P < 0.05). 2) With respect to soil microbial diversity indices (i.e. OTU number, Chao 1 index and Shannon index), they were not significantly different between the T1 treatment and CK in the first CS, but were significantly higher in the T1 treatment than in CK in the second and third CSs, while they were higher in the T2 treatment than in CK in the first CS, and were significantly increased in T2 treatment as compared to T1 in the third CS (P < 0.05). The Simpson index showed no significant difference among three treatments. 3) Compared with CK, both T1 and T2 treatments significantly increased the relative abundances of Proteobacteria, Actinobacteria, Firmicute, Chloroflexi, Gemmatimonadetes, Nitrospirae, but decreased the abundance of Acidobacteria and Bacteroides. 4) Soil total C, N, P and K, and available N and K had significant positive correlations with microbial diversity indices and Simpson index.

  Conclusions  In-situ vermicomposting is more efficient than ex-situ vermicomposting in enhancing soil fertility and increasing soil microbial diversity. In addition, in-situ vermicomposting increases the abundances of Chloroflexi, and Gemmatimonadetes, and decreases the abundance of Acidobacteria and Bacteroides which are associated with continuous cropping obstacle, thereby contributing to alleviate continuous cropping obstacle. Therefore, it is recommended to use earthworm in-situ vermicomposting in tomato production.