INTERACTIONS OF EARTHWORMS WITH SOIL PHYSICAL CONDITIONS INFLUENCING PLANT GROWTH

Earthworms have been credited with creating channels that allow deeper root penetration through hardpans or unstructured soils; however, the benefit of earthworm channels decreases as the volume of alternative low resistance pathways for root growth increases. Improved root growth does not always result in increased crop growth. Some earthworm species incorporate surface residue and surface-applied lime and fertilizers. Earthworm channels can increase infiltration and reduce runoff, increasing soil water availability or, possibly, deep percolation to maintain favorable water status for crop growth. Pot studies often indicate increased plant growth in response to unrealistically high earthworm inoculation rates; however, only a few field studies indicate any plant growth increases, mainly for pastures, orchards, and small grains. The mechanisms and dynamics of plant response to earthworms needs to be more thoroughly explored, especially in field studies at realistic inoculation rates and with statistical comparisons.