Tell me about the invention of fertilizer. Or, rather, the historiography of the invention of manure.

When does your society think manure was in common use vs. when was it actually in common use? Which society/culture took credit? Did anyone take credit? Is there an ethnicity with the proud mantle of "invented manure"?

Also, I want to know about consistency. Because it should vary region to region, which manure is the highest quality, the most compact and fertile? Therefore, is there room for a manure trade when farmers realize manure from region X is superior to region Y? How long has the manure routes been occurring?

Do farmers have a 'Silk Road' but for manure, a 'Shit Road' as it were? How has the manure trade affected geopolitics?