Twelve experimental treatments were applied to microcosms
in a factorial experiment: three plant treatments
(no plants, wheat plants [Triticum aestivum] or
clover plants [Trifolium repens]) × two crop residue
additions (450 gm–2 of either wheat [0.3% N] or clover
[4 % N] residues incorporated to 10 cm) × two earthworm
treatments (none or 600 adult earthworms m–2
[Aporrectodea caliginosa with average biomass of
0.74 g fresh weight/earthworm]). The number of earthworms
used (600m–2) is typical of earthworm populations
found in New Zealand mixed cropping soils
(Fraser et al. 1996).
Wakanui silt loam soil (Udic Dystrocrept, USDA
Soil Taxonomy; total C = 2.6% ; total N = 0.2%;
pH= 5.8; Olsen P = 25; CEC = 14me/100g; mean
weight diameter = 0.5) was sieved (< 2 mm) and inherent
earthworms and cocoons removed. Soil microcosms
were constructed using PVC cylinders of 15 cm