We don't have an expense account in the standard chart of accounts that is appropriate for that. You will need to add an expense account. The only thing I'd recommend keeping in mind when creating the account is to set it up in the section that reports for the crops you sell. For instance, if I grow wheat and canola I should have a section of expense accounts called Grain Expenses and another section called Oilseed Expenses. If I irrigate both crops then I'd want two irrigation expense accounts, one in each section.
I hope that makes sense!
