  Measurements of the dc transport properties and the low-frequency
conductivity noise in films of charge ordered Nd_0.5Ca_0.5MnO_3 grown on Si
subtrate reveal the existence of a threshold field in the charge ordered regime
beyond which strong non linear conduction sets in along with a large broad band
conductivity noise. Threshold-dependent conduction disappears as T -> T_{CO},
the charge ordering temperature. This observation suggests that the charge
ordered state gets depinned at the onset of the non-linear conduction.
