Interactions between earthworms (Aporrectodea caliginosa), plants and crop residues for restoring properties of a degraded arable soilThe 7th international symposium on earthworm ecology · Cardiff · Wales · 2002

Abstract

Summary A laboratory experiment was conducted to determine how the interactions between earthworms, soil microbes and plant roots influence the restoration (soil structure formation, nutrient availability and organic matter pools) of a degraded arable soil in the presence of low or high quality organic resources (crop residues). Soil microcosms (19 cm diameter by 30 cm deep) were packed to appropriate soil densities with sieved, homogenised soil, collected from a field that had previously been degraded by long term arable cropping. Any inherent soil macrofauna (especially earthworms) were removed from the soil by sieving and hand sorting prior to starting the experiment. Twelve treatments were applied to the microcosms as follows: three plant treatments (either no plants, wheat plants or clover plants were grown in the microcosms) × 2 crop residue additions (either wheat straw or clover residues incorporated to 10cm depth) × 2 earthworm treatments (none or 600 earthworms m –2 [ Aporrectodea caliginosa ]). Each treatment was replicated four times and microcosms were destructively sampled on three occasions (after 4, 8 and 16 weeks respectively) following initiation of the experiment. All of the microcosms were housed in a growth chamber where temperature, light and moisture could be controlled. A range of analyses were performed on both the plants and the soil in the respective microcosms at each sampling time. Measurements performed included physical (soil aggregate stability, plant shoot and root dry matters), chemical (total C and N, mineral N, pH), and biological (microbial biomass C and N, earthworm weights and numbers) analyses. Earthworms significantly increased the growth and N uptake of wheat plants where low quality (wheat) residues were added, however they had relatively little effect where high quality (clover) residues were used. Earthworm biomass was supported best by clover residues and wheat plants, and in the presence of clover residues earthworm activity increased soil mineral N levels. The increase in mineral N availability with clover residues markedly increased wheat production and N content. Earthworms were also much more important than plants at increasing soil aggregate size. However, whereas earthworms had relatively little effect on aggregate stability, plants had a large effect and wheat plants were shown to be more important than clover plants.