Soil restoration takes time, yes, which is why one of the methods Ruffin suggested was to use crop rotation, which allowed other useful crops (food, fodder, etc) even when the soil is not growing tobacco. There were various methods he and others proposed, but the net effect was that tobacco production was still highly profitable in Virginia, even if it took a few years to restore the most exhausted soils (such as around the Tidewater).I defer to you on this topic, as I know how much you've researched it, but just to test a couple of things:
On tobacco, doesn't soil restoration take time? There's also the issue that tobacco (and rice) requires more skilled slaves than cotton does, which ups their price and makes the trade less profitable.
In terms of slave prices, the basic price of slaves in OTL was set by the sheer scale of the cotton boom, and the high returns it generated. This led to cotton planters bidding against each other for the limited supply of slaves, and in turn pushed up prices to a much higher point than they would have been in the absence of cotton. So while skilled slaves still commanded higher prices than unskilled slaves, in a hypothetical no-cotton South, the overall slave prices are going to be lower, not higher, even for skilled slaves.
Sources differ on how much grain had a productivity advantage per worker with slavery. The crucial advantage of slavery, though, was that it allowed the more efficient farmers to expand and push out small farmers. This is because in the nineteenth century agricultural USA (both North and South) land was cheap and labour was expensive, and in particular, hired labour was unreliable. Even the most efficient free farmer couldn't expand their farm beyond what could be farmed by their own family with occasional hired help. (Hired labourers tended to quit, go on strike, depend too high prices, or go and start their own farm.)I accepted that grain was more efficient than using slavery, but my understanding was that it wasn't a huge differential (which is what I think you need for people to do logical backflips to deny the obvious moral repugnance of slavery over a vigorous abolition campaign)
Slavery changed that because slaves couldn't go and start their own farm. This allowed the more efficient/lucky slave-using farmers to expand in a way which wasn't possible with free soil, and take advantage of economies of scale and access to greater capital which free farmers could not. This process applied to grain as much as to cotton.
It's large enough to permit a very profitable sugar sector, with strong political influence.On sugar, the coastal areas of the Gulf is a pretty slim slither of land, isn't it?
More broadly, if the cotton gin is delayed, what happens is that there is no one dominant crop throughout the South, but rather that there would be a mixture for uses for slaves, each of them profitable enough in their area: tobacco, grains/livestock, rice, sugar, long-staple cotton, urban manufactures, etc. This is akin to the pre-ARW pattern, where there was tobacco, rice and indigo, with smaller use of other crops, artisanal work, etc.