Research objectives

The overall aims of this research project were to investigate:

• the interactive effects of CGW addition and earthworm activity on tree growth and survival on reclaimed landfill,
• the interactive effects of CGW addition and earthworm activity on the biological, physical and chemical quality of reclaimed soil under woodland,
• the community dynamics of naturally and artificially introduced earthworms on landfill sites, and responses to tree establishment and CGW addition.

Composted Green Waste being transported to an experimental plot for incorporation to the soil.

Results

A large-scale field experiment and a nursery-based experiment revealed the responses of the tree species Italian alder and Norway maple to CGW and earthworm addition in reclaimed soil. Findings included:

• A positive synergistic effect of CGW addition and earthworm activity leading to significantly growth of both tree species.
• CGW addition significantly increased levels of soil organic carbon and essential plant nutrients, with earthworm activity increasing the accumulation of organic carbon into the soil.

Additional laboratory-based research revealed the performance of four common UK earthworm species in reclaimed soil and the palatability of CGW and Italian alder and Norway maple leaf material. We demonstrated that CGW and leaf material from both tree species can support earthworm establishment on landfill, and that two particular species of earthworm (black-headed and green worm) are suitable candidates for inoculation to reclaimed soil.

Finally, a survey of a newly reclaimed site showed that natural colonisation of reclaimed land by earthworms can occur rapidly (within 2 years), where soil quality is sufficient, and legacy soil materials are stockpiled and applied following best practice guidance.