Rural Industries Research & Development Corporation

Research Compendium 1993 - 1994

Research Project

REHABILITATION OF DEGRADED SOIL BY THE ACTION OF SOIL FAUNA AND PLANT ROOTS

Objective

To develop management strategies that accelerate the physical and chemical rehabilitation of degraded soils by establishing and encouraging soil macro-biological activity.

Background

Long-term declines in the structure and fertility of farming soils are being reversed through farmer adoption of practices that reduce cultivation and conserve plant organic matter. However, merely halting practices that degrade the soil only results in a slow recovery of the natural processes that restore soils.

The development of management practices that encourage biological activity would accelerate the natural recovery processes in soils. Earthworms, through their burrowing, casting, and mixing activities, offer the potential, in combination with appropriate soil management, to rapidly accelerate the natural recovery of degraded soil.

Research

Field studies surveyed earthworm populations from different soil types and environments across north-east Victoria and southern New South Wales, and under different farming practices.

Postgraduate studies at LaTrobe University focused on how the growth of plant roots in compacted soil is improved by the discontinuous burrow systems formed by the earthworms commonly found in farming soils. In particular, the impact of burrows filled with earthworm costs on the growth of ryegrass roots was examined.

Outcome

The survey found low numbers of earthworms in both cropping (51 m -2 ) and pastoral (63 m -2 ) soils. Across all sites, the diversity of earthworm species was low 2 site -1 ) and introduced earthworms were dominant. There were no earthworm species that actively burrow below 0.2 m depth. High mortality and low reproduction rates characterised the mass-rearing of one deep-burrowing species which is established in Tasmania. More earthworms were found under cereal stubbles left standing, or mulched, than with incorporated stubbles.

The PhD studies showed that, where earthworms had burrowed through compacted soil, the mass of ryegrass roots increased. About 80 per cent of the burrows were filled with casts. In dense soils, roots prefer to grow in open burrows, although root growth can decrease because of the reduced contact between roots and soil. In burrows filled with earthworm casts, root growth is greater than in compacted soil because the casts are less dense, and softer than the surrounding soil. In addition, the casts shrink slightly after they are deposited, allowing roots to grow between the burrow wall and the casts.

RIRDC Project No: DAV-48A

RESEARCHER: Mr P J Haines Dr B M McKenzie

ORGANISATION: Dept of Agriculture Vic. School of Agriculture

RUTHERGLEN VIC 3685

PHONE: 060 32 9208 03 479 2184

PUBLICATIONS:

Haines, P J (ed.), 1991, Earth Worms: Improving Soil for Agriculture. Proceedings of a Conference held at Wangaratta, 11 September 1991. Australian Institute of Agricultural Science Occasional Publication No. 62.

Hirth, J R, McKenzie, B M and Tisdall, J M, 1995, The volume density of earthworm burrows in compacted cores of soil as estimated by direct and indirect methods. Biology and Fertility of Soils (accepted).

Hirth, J R, McKenzie, B M and Tisdall, J M, 1995, Root growth towards biopores filled with earthworm casts. I Soil Biology and Biochemistry.

Last updated: 10 October 1996
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