Fig. 2. Methane (top) and O₂ concentrations (bottom) during incubation of extracts of natural surface crust material from storages with untreated slurry (UCS), and of straw used as an artificial surface crust on storages with digested slurry (DCS). The subscript terms C and 0 indicate presence or absence, respectively, of an additional solid cover. The data represent mean ± standard error (n = 3).