  In the last few years several experiments have shown that the cosmic ray
spectrum below the knee is not a perfect power-law. In particular, the proton
and helium spectra show a spectral hardening by ~ 0.1-0.2 in spectral index at
particle energies of ~ 200-300 GeV/nucleon. Moreover, the helium spectrum is
found to be harder than that of protons by ~ 0.1 and some evidence for a
similar hardening was also found in the spectra of heavier elements. Here we
consider the possibility that the hardening may be the result of a dispersion
in the slope of the spectrum of cosmic rays accelerated at supernova remnant
shocks. Such a dispersion is indeed expected within the framework of non-linear
theories of diffusive shock acceleration, which predict steeper (harder)
particle spectra for larger (smaller) cosmic ray acceleration efficiencies.
