Sometimes a Landlord has a total figure that he wants, say $20,000 in your case.   So, you're either paying $200 for the 100 acres or $222 for the 90.  

Reason I say this, know of a tenant that lost a farm because he and Landlord were quibbling about the tillable acres.   It was a small percentage of the total.   Landlord wanted X amount of dollars total.   Tenant couldn't wrap his head around that.