I'm remembering my uncle's ranch in Oklahoma. I visited there when I was a teen. To put it mildly, there was always, always a to-do list. It never ended. Some occupations are extremely demanding, and farming is one of them. But you know that!
I hope it all works out. I'm also remembering my college best friend's father, who ran a mom-and-pop grocery store at the front of their house. They worked that store six days a week, early morning until late night, and her dad *never* took a day off... until my friend married. Then he (gasp!) closed the store for the weekend of the wedding. He had such a good time that he kept the store closed for another week and he and Mama took a little vacation!
But you can't close a farm. It has to keep going like the Energizer Bunny.
Try not to be defensive. Be very, very appreciative of your husband. Being away from work is a huge deal for him. The fact that he's doing it to please you is major. So if he worries about what's happening at home, appreciate that he's really being on *your* side. Let him call to check on things at the farm when he feels he needs to. A part of his brain will always be on the job. It's the way guys are.
If this trip can help your husband relax a little, it will good for him. And do you have a good friend or neighbor who would be willing to double-check on your FIL every day?
It's your call to decide when (and if) you let your husband know that you had guilt feelings about laying the guilt trip on him. Sometimes this opens an avenue for good conversation.
When you get home, you'll want to help to catch up with the work. Maybe you'll both be surprised to find that things have gone relatively well.
Sometimes life doesn't run pleasantly. ANY time, whichever and however one of you gets what they want, always remember that you're a team.