Vermicompost leachate improves seedling emergence and vigour of aged seeds of commercially grown Eucalyptus species

Vermicompost leachate (VCL) is a liquid generated by earthworms and microorganisms during the conversion of organic matter into vermicompost. Vermicompost leachate is rich in nutrients and believed to contain both known and unknown plant growth substances, which are beneficial to plants. Four-year-old seeds (artificially aged) of Eucalyptus dunnii, E. nitens and E. smithii were subjected to VCL at different concentrations. In comparison to the control, the percentage of emerged seedlings of all three species improved significantly (p < 0.05) by more than two to three times when treated with VCL. Treated seedlings showed better growth performance than untreated ones at both first and second harvest, 75 and 150 d after sowing, respectively. Eucalyptus dunnii achieved the highest seedling vigour index (SVI) at the lowest VCL concentrations of 1:5. In contrast, the SVI of E. nitens was maximum at the highest concentrations of VCL (1:20). The best SVI of E. smithii was obtained at VCL concentrations of 1:10. These results suggest that the influence of VCL on SVI of the eucalypt species tested was concentration-dependent. The absolute seedling vigour rate per day was also improved with all the tested concentrations of VCL, with some exceptions for E. dunnii seedlings. The order of response to VCL by the species can be summarised as E. smithii > E. nitens > E. dunnii. The results of this study suggest that VCL can be used to supplement chemical fertilisers. The liquid nature of VCL should be convenient for application both under nursery and field conditions. However, trials under field conditions are required.