I see no need to burn it at all. Segregate the nitrate into a biscuit tin with a couple vent holes and keep it under 38C/100F. It's survived a century in a hot house, it'll be fine for the move as long as you don't leave it locked in a steel shipping container out in the sun. We're not talking about 5000 feet tightly wound, with much higher concentrations of gas and the dense packing causing self-heating from (and therefore acceleration of) decomposition.