There's a lot of farmland and ranch land in the US that shouldn't be farmland or ranch land. They're too dry, too hot, and competing for water resources with people and natural (sometimes endangered) ecosystems.

So, maybe it's something that should be encouraged; the food those farms and ranches produce would need to be replaced by food grown in more appropriate climates, and we'd need to rethink our recent "local food" movement, in some regards, but agriculture, and particularly animal agriculture, are an ecological disaster almost everywhere they exist. Couple that with limited water resources (where a lot of agriculture takes place in California, Texas, Arizona, and New Mexico) and you've got a recipe for serious problems long-term.

That said, agriculture could also shift. Less water-intensive foods, more foods that are appropriate for the area they're being consumed in.

Anyway, I think solar farms replacing agricultural farms could be a net win for the environment, even before considering the improvements that come from turning off coal-fired plants.