Billions, it would appear. But that doesn't necessarily mean that billions of acres can be taken out of service.
While local conditions don't perfectly extrapolate to the world, remember that 100% of my acres grow human food when observed over the span of more than one year. The 35% animal food production seen in a single year is the outcome of the crop rotation.
Certainly, I'd be far more profitable if I could reliably grow beans for human consumption over and over and over, but Mother Nature is a harsh mistress.
While local conditions don't perfectly extrapolate to the world, remember that 100% of my acres grow human food when observed over the span of more than one year. The 35% animal food production seen in a single year is the outcome of the crop rotation.
Certainly, I'd be far more profitable if I could reliably grow beans for human consumption over and over and over, but Mother Nature is a harsh mistress.