Suitability of wheat straw decomposition, cotton strip degradation and bait-lamina feeding tests to determine soil invertebrate activity

Abstract

The activities of earthworms, springtails and mites in the decomposition of different substrates were examined by applying three different test methods: wheat straw degradation, the cotton-strip assay and the bait-lamina test. The main aim was to determine the potential of these three methods to describe the (direct and indirect) contribution of soil invertebrates to decomposition processes in soil. Animals were introduced at different densities to mesocosms consisting of intact soil cores taken from grassland. Wheat straw mass loss, determined after 27 days, and cotton tensile strength loss, measured after 14 days, did not significantly differ for the different densities of earthworms, springtails and mites. These findings indicate that cellulose degradation and wheat straw decomposition are more dependent on microbial activity, rather than on the abundance and activity of soil invertebrates. Soil microbial activity, measured as dehydrogenase activity at the end of the 75-day incubation period, did not show any correlation with animal density. Bait-lamina consumption rate was highest for the mesocosms containing earthworms, and increased with increasing earthworm density. Bait-lamina consumption in the mesocosms inoculated with springtails or mites only was not significantly different from that in the controls without animals. In the case of the mites this might at least partly be explained by the low densities used in this experiment. It may be concluded that whilst the bait-lamina test gives the best reflection of the biological activity of soil animals, in particular earthworms, wheat straw and cotton strip decomposition rates are more indicative of microbial activity in the soil.