[jfengel]

The market is saturated. American farmers already buy as much alfalfa as they want. The next unit of alfalfa is worth basically nothing to them.

To sell more alfalfa in America you'd need more farms to raise more cattle (the main use for alfalfa), which would put even more strain on the American water supplies. That would produce more meat, which you could sell to China, but it would be more expensive than the Chinese homegrown beef, which they'd buy more of.