I first heard it in Short History of Progress. https://www.youtube.com/watch?v=AsPMaGdg_38 https://www.youtube.com/watch?v=AsPMaGdg_38 Wheat yields progressive

I first heard it in Short History of Progress. https://www.youtube.com/watch?v=AsPMaGdg_38 https://www.youtube.com/watch?v=AsPMaGdg_38 Wheat yields progressively fell as salt accumulated in the ground. They switched to barley until that crop failed too. According to the book, almost all ancient agriculture was unsustainable. If not because of the irrigation, it was because plowing caused too much soil erosion. The only places that could get away with it long-term were Egypt and China, because of the flooding and lime replenished the soil.