<br/>Inoculation of earthworms can help to restore or ameliorate land qualities. Earthworms create burrows and alter the structure of the soil matrix, which influence the water infiltration, drainage, water retention and the aeration of the soil. The way and rate of the development of earthworm burrow systems are practically unknown, and form the core of this thesis.<p>When studying the relation earthworms - soil properties, correlations between earthworm activity and soil properties are commonly found, but cause and effect are hard to separate. This problem can be resolved in part by studying a chronosequence of earthworm burrow systems and associated earthworm-affected soil properties. Two of such chronosequences, which developed after inoculation of earthworms in pastures formerly without earthworms and covered 0 to 20.3 y of earthworm activity, were considered in this study.<p>In the most intensively studied chronosequence the average dispersal rate of the earthworms was 6.3 m.y <sup><font size="-2">-1</font></SUP>in the first seven years following the inoculation. The rate strongly increased up to an average 29.3 m.y <sup><font size="-2">-1</font></SUP>in the next three years. This accelerated dispersal is most likely related to a change in food supply.<p>To reveal the mode and rate of development of earthworm burrow systems, six of these systems were mapped three-dimensionally. Density and architecture of the burrow systems changed quickly and strongly responded to changes in the mass of the earthworm community. The burrow systems consisted of mainly vertical burrows, many of which were short (<6 cm) and only few of which reached lengths greater than 30 cm. Year-to-year variations, differences in burrow systems between the two chronosequences, and burrowing efficiency of the earthworms could be related to differences in earthworm activity.<p>The highly dynamic nature of earthworm burrow systems indicated that both formation and destruction of burrow systems need to be considered. The destruction rate of earthworm burrows and its controlling factors were assessed by following the fate of artificial earthworm burrows in one of the pastures, and by thin section analysis of natural burrows. At and close to the soil surface trampling by cattle was the main cause of burrow destruction. At greater depth (22.5 cm) casting by earthworms was found to be the most important source of destruction.<p>Burrows increased hydraulic conductivities ( <em>K</em> ) of the fully water saturate soil and of the soil matrix close to saturation. The structure of the subsoil strongly influenced the <em>K</em> of individual burrows. The change in structure of the topsoil by earthworm activity increased <em>K</em> of the unsaturated soil matrix.
|Qualification||Doctor of Philosophy|
|Award date||17 Apr 1996|
|Place of Publication||S.l.|
|Publication status||Published - 1996|
- hydraulic conductivity
- soil density
- pore volume