Movement of oxygen and subsequent microbial development and heating in
corn silage were measured over four days at 5, 20, 35, and 50 cm from
the exposed face in laboratory-scale (60 x 15.5 cm diameter) PVC silo
s. In all six trials, most microbial activity occurred at the 5-cm lev
el. Acetic acid bacteria initiated heating in all trials although yeas
ts were significant in two trials. Bacilli were not important until si
lage pH was above 5 and were associated with a secondary temperature r
ise in four trials. Oxygen entering the silage at the open face was ut
ilized principally near the face, and temperatures above 40-degrees-C
were observed only at the 5-cm level. Heating at 20 cm occurred in all
trials, but appeared to result from heat transfer from the active zon
e rather than from microbial activity at that depth. A diffusion-based
, one-dimensional model of aerobic deterioration in silage reasonably
predicted oxygen, temperature, and microbial numbers although the pred
icted progression of deterioration relative to the exposed face was co
nsistently too fast. Model predictions were improved by reducing the c
alculated porosity for diffusion by 30%.