Role of earthworms in straw decomposition in a winter cereal field

The decomposition rate of wheat straw buried in the soil was studied by means of litter bag experiments conducted over three successive years in a winter cereal field in Co. Kildare, Ireland. The rate of mass loss was well described by an exponential decay function, but a simple linear model also gave a good fit and facilitated comparisons between treatments and years. Mass loss was greatest from litter accessible to earthworms in all three years, but the earthworm effect was greatest in the first year when the rate of ash-free mass loss from coarse (7 mm) mesh bags was 313 mg month−1 compared with 234 mg from fine (1 mm) mesh bags. The corresponding rates for the second and third years were 341 and 295, and 376 and 336 mg month−1 from coarse and fine mesh bags, respectively. A possible reason for the reduced earthworm influence over time was the decline in numbers of Lumbricus terrestris with continuing arable cultivation.