I thought so too, but Wiki says fertilizer was in fact the main usage. I suppose you get many extra units of grain per unit of added guano. https://en.wikipedi

I thought so too, but Wiki says fertilizer was in fact the main usage. I suppose you get many extra units of grain per unit of added guano. https://en.wikipedia.org/wiki/Guano https://en.wikipedia.org/wiki/Guano "As a manure, guano is a highly effective fertilizer . . . Guano was also, to a lesser extent, sought for the production of gunpowder and other explosive materials. The 19th-century guano trade played a pivotal role in the development of modern input-intensive farming."