Guano [gwah-noh] is the accumulated excrement of seabirds and bats. As a manure, guano is a highly effective fertilizer due to its exceptionally high content of nitrogen, phosphate and potassium: key nutrients essential for plant growth. 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, but its demand began to decline after the discovery of the Haber–Bosch process of nitrogen fixing led to the production of synthetic fertilizers. The demand for guano spurred the human colonization of remote bird islands in many parts of the world, resulting in some of the first examples of U.S. colonialism and the expansion of the British Empire.
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The Daily Omnivore 