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Protons with energies up to ~ 10 15 eV are the main component 1 of cosmic rays, but evidence for the specific locations where they could have been accelerated to these energies has been lacking 2 . Electrons are known to be accelerated to cosmic-ray energies in supernova remnants 3,4 , and the shock waves associated with such remnants, when they hit the surrounding interstellar medium, could also provide the energy to accelerate protons. The signature of such a process would be the decay of pions (π 0 ), which are generated when the protons collide with atoms and molecules in an interstellar cloud: pion decay results in γ-rays with a particular spectral-energy distribution 5,6 . Here we report the observation of cascade showers of optical photons resulting fromγ-rays at energies of ~ 10 12 eV hitting Earth's upper atmosphere, in the direction of the supernova remnant RX J1713.7-3946. The spectrum is a good match to that predicted by pion decay, and cannot be explained by other mechanisms.

When RS was applied at a rate corresponding to 6 t ha '•, the percentage contributions of RS, SOM, and RP carbon to CH 4 emission throughout the period of rice growth were 42%, 18-21%, and 37-40%, respectively. The values for SOM and RP carbon for the treatment in which RS was not applied were 15-20% and 80-85%, respectively. Seasonal variations in the percentage contribution of soil organic carbon to CH 4 emission were small in the range between 13% and 30% for the pots with RS and between 15% and 24% for the pots without RS. In the RS-applied treatment, RS and SOM accounted for almost 100% of the CH 4 carbon early in the period of rice growth, while 65-70% of the CH 4 emission in the milky stage was derived from RP carbon.

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