As they decompose, mulches add nutrients to the soil, and if composed of small-enough particles, worms may slowly eat the mulch and incorporate it into the soil.
(they; decompose; ) (mulches; add; nutrients; to the soil) (worms; may slowly eat; the mulch) (worms; incorporate; it; into the soil)
they mulches worms worms
decompose add may slowly eat incorporate
nutrients to the soil
the mulch
it into the soil