Large-scale vermicomposting: emission of nitrous oxide and effects of temperature on earthworm populationsThe 7th international symposium on earthworm ecology · Cardiff · Wales · 2002

Abstract

Summary A large-scale, outdoor vermicomposting system was monitored for 80 weeks. Earthworm populations were recorded for 60 weeks in unheated beds operating at ambient temperatures (34 weeks at 6.3 ± 2.3 °C) and in heated beds controlled at 13.7 ± 0.8 °C for 34 weeks. Both blocks of beds were at ambient temperatures for the remaining 26 weeks. Earthworm biomass and the numbers of hatchlings and cocoons produced for the heated beds were found to be significantly greater than for the unheated beds. Nitrous oxide fluxes in winter (week 60) were 3.2 ± 0.3 mg m –2 h –1 (unheated beds), 1.8 ± 0.3 mg m –2 h –1 (heated beds), and these were significantly different to the control beds (0.1 ± 0.0 mg m –2 h –1 ). Emissions during summer (week 80) were 20.1 ± 3.0 mg m –2 h –1 (unheated beds), 21.3 ± 2.8 mg m –2 h –1 (heated beds) and these were significantly different to the control beds 3.9 ± 1.7 mg m –2 h –1 . No relationship between earthworm density and nitrous oxide flux was found for the large-scale beds. However, in a subsequent laboratory experiment, nitrous oxide emissions were positively correlated with earthworm density (R 2 = 0.76). Maintaining moderate bed temperatures for vermicomposting systems during low ambient temperatures can significantly increase earthworm density. Vermicomposting systems have the capacity to emit high levels of nitrous oxide and earthworms appear to be primarily responsible for this. The environmental impact from nitrous oxide emissions appears to be comparable to other waste processing operations. Further research is required into ways of minimising emissions especially from vermicomposting systems operating at high earthworm densities and high waste processing rates.