In the 1790s, an Oxford student introduced using guano (bird p | The Open University

In the 1790s, an Oxford student introduced using guano (bird poop) as fertiliser. He spread guano across the university lawn, using it to spell G U A N O. The lawn was soon scrubbed, but when spring came, the word GUANO was clearly visible, growing higher and thicker than the rest of the grass.

@TheOpenUniversity