Influence of earthworms on some soil chemical and physical properties, and the growth of ryegrass on a soil after topsoil stripping - a pot experiment

In the Wellington region, topsoil is being stripped from land for various purposes. A glasshouse pot trial over 12 months examined the potential of earthworms for improving the productivity of the remaining soil. Inoculation with Allolobophora caliginosa (Savigny) greatly enhanced early growth of perennial ryegrass and increased dry matter production throughout the trial. Earthworm numbers were monitored and showed marked differences in stages of growth according to the presence or absence of ryegrass. In particular numbers of both medium and small immature earthworms were higher in the presence of ryegrass indicating depression of breeding without ryegrass. Nutrient uptake for most major and trace elements by ryegrass was increased in the presence of earthworms. Some physical properties which contribute to the structure of the soil were measured. Earthworms by themselves have little effect, but combined with ryegrass, a trend to decrease bulk density and increase the proportion of small and medium macropores (0.30‐0.06 mm) was observed in the top 5 cm of soil in the pots. These results indicate that earthworms may have a marked beneficial effect in improving ryegrass productivity on soil after topsoil stripping.