Earthworms for inclusion as an indicator of soil biological health in New Zealand pastures

Soil health encompasses the physical, chemical and biological components of the soil. In New Zealand, current officially recorded soil quality indicators do not include a biological indicator. Earthworms have long been recognised as useful indicators and as such offer an option for addressing the lack of a biological measure for on-farm assessment of soil health. In this paper we review the use of earthworms as indicators of soil health using both abundance and ecological group diversity. To use earthworms as an indicator of soil biological health, we recommend target earthworm abundances of >400 ind./m2, within which each of the three earthworm ecological groups (epigeic, endogeic and anecic) should be represented at a minimum of 25 ind./m2. When earthworm populations are at these target levels, the greatest benefits to soil functions can be realised. If earthworm populations are below target levels management practices can be appropriately altered to improve the soil environment and enhance their populations.