If the farm is in your wife's name and turns a profit, she can contribute an amount equal to or less than the farm profit to an IRA - there are other limiting factors, such as age, but no earned income equals no IRA contribution. She may also be able to contribute to a spousal IRA on your behalf, up to her earned income limit.
If the farm is your operation, you need to correct the ownership and then the same is true, only reversed.