The experimental SMS units consisted of polyethylene tubes(33 cm × 9.3 cm ø), having a surface area of 68 cm2 and sample volume of 2241 cm3. The tubes, closed on the bottom with a lid, were filled with 1000 g moist soil (800 g dry weight plus 200 ml aqueous microbial substrate). Experiments were performed in temperature controlled rooms (variation in temperature was ±1◦C). After the addition of animals, each unit was covered with a perforated lid,weighted and transferred to the controlled temperature test room with a 12 h:12 h light:dark cycle. The soil water content was maintained by replenishing water loss weekly.