The defecated casts become stable after drying. Stewart et al. Incorporation of litter by earthworms in apple orchards can be an important mechanism for preventing outbreaks of scab fungus, spores of which are transmitted from litter to new foliage by spring rains. Incorporation of surface litter may be an important function of earthworms in no-tillage agroecosystems. Earthworm casts are sources of nutrients for plants.
Earthworms increase the amount of nitrogen mineralized from organic matter in soil.
This occurs because earthworms reduce the amount of substrate available to other decomposers, and because earthworms ingest other decomposer organisms as they feed. This process would tend to accelerate nutrient cycling rates. Agricultural soils are generally dominated by species adapted to disturbance, low organic matter content, and a lack of surface litter. Earthworm populations are usually significantly depressed in cropped fields relative to pasture or undisturbed lands. Lumbricids in a South African soil were decreased by cultivation to about one-third of original levels.