The soil was sampled in the 0–10 cm layer of a fallow in the
red river delta (Dong Ngac commune, Ha Noi, Vietnam) where M.
posthuma is naturally observed. The soil was air-dried and sieved at
2 mm to discard stones and litter residues. It is described as Eutric
Fluvial (FAO, 1988) with low OM content and low nutrient content
and is mainly sandy loam (61.0% sand, 28.7% silt and 10.3%
clay). Compost and vermicompost were produced in a farm in Dong
Cao Village from domestic buffalo manure after three months of
maturation in two different and separated units, as reported by
Jouquet et al. (2010). They were air-dried for one week and sieved
at 1 cm. The earthworm species used to produce the vermicompost
was Eisenia andrei. Chemical properties of the soil and organic
amendments are given in Table 1.