Rural Industries Research & Development Corporation

Research Compendium 1993 - 1994

Research Project

EFFECT OF EARTHWORMS ON SOIL

Objectives

• To determine the effects of two contrasting earthworm species (A. trapezoides and A. rosea) on the release of total CO 2 and 14 CO 2 from (a) freshly added plant materials on the soil surface or incorporated, (b) older plant residues, and (c) the native soil organic matter.
• To determine the role of earthworm activity in exposing physically protected soil organic matter to biological decomposition.
• To examine the influence of soil type on the above processes.

Background

Earthworms are an integral part of sustainable farming systems. They have considerable impact on soil through their feeding, burrowing and casting activities. To effectively manage farming systems, it is essential that the role of earthworms in carbon dynamics is established and quantified.

Research

Earthworms were confined in containers filled with soil moistened to -10 kPa, compared to field bulk density and amended with 14 C-labelled plant materials. They were incubated within 1 L sealed glass jars at 16°C and the 14 CO 2 and 12 CO 2 released monitored. At the beginning and end of the incubation microbial biomass and distribution of microaggregates were measured .

Outcome

Under the experimental conditions, earthworms did not increase the rate of decomposition of high C/N ratio, wheat residues or low C/N ratio legume residues on the soil surface or incorporated into the soil. Earthworms did, however, significantly increase the decomposition of 'native' soil organic matter, with A. rosea being more effective than A. trapezoides.

This was accompanied by a decrease in silt-sized aggregates in many soils. Some soils were more susceptible to aggregate breakdown than others but no correlation could be found between soil properties and susceptibility to microaggregate breakdown.

Implications

Although this was only a laboratory experiment, implications are that earthworms have little overall effect on residue decomposition under optimal moisture conditions but may have a negative effect on soil microstructure in certain soil types.

RIRDC Project No: CSO-1A

RESEARCHERS: Morris Amato and Jan O Skjemstad

ORGANISATION: CSIRO Division of Soils

PHONE: 08 303 8531 or 08 303 8427

Last updated: 10 October 1996
Copyright © RIRDC
Index of RIRDC Projects URL
http://www.rirdc.gov.au/pub/compendium/93-94/index-b.html