As Shelby and Chris have said, they are very similar. However, "inhuman" is much more extreme. It means "treated as if someone isn't human." For example, "Adolf Hitler's treatment of Jews was inhuman." This means Hitler treated Jews like they weren't people. In general, "inhuman" is only used when describing treatment of humans because it means "treated like NOT human."
"Inhumane" generally means "cruel." For example, "That man's treatment of animals is inhumane." This means the man is very cruel to the animals.
In your sentence, "inhumane" is probably best. Unless the farming treats humans wrongly, use "inhumane."
Hope this helped! Let me know if you have any questions.