They were extremely inefficient as farm equipment. They required food, shelter, and monitoring all year long but most were required only for planting and harvesting. Their only three values over machinery that they could be made into "house servants", as collateral for loans (rather than going all in and "Betting the farm"), and that you could simply allow them to follow their nature and breed more.
They were inefficient, which is why as soon as machinery became available they were replaced. If our Confederate brothers had tractors available, they would have used them instead.
No, they would have fought against improved farming techniques. Tractors would have made slaves worthless and therefor useless as collateral for the loans which made the bankers wealthy.
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