Fertilizer

The deployment of war machines (tanks) refitted for agriculture (tractors) was the nail in the soil's coffin.

- John Deere and Cyrus McCormick machines allowed more land to be cultivated than ruminants under management could manure (reapply fertility).

- The new equipment drove farmers to cultivate beyond their ability to naturally manage so the scene was set for fertilizer manufacturers (as they transitioned from making high explosives in wartime) to "take up that space".

- Land needs at least 2 head of cattle per acre to be properly manured so a a quarter section of land means the management of 80 head of cattle. A full section (640 acres) requires 320 and that's a minimum.

- Because it's easier to deploy sacks of nitrogen fertilizer a few times per season than manage 320 head of cattle all year long, fertilizer displaced the ruminants and now we have Confined Animal Feeding Operations because beef is still in demand.