@jkelsey "I think I am going to extend their return and pay the tax owed via EFT and file them once the form(s) have all been approved."

The March 1 (this year, March 2) date is only allowed when the return is filed by that date.  If you just want to make a payment with no return, that was due on January 31. It only had to be 2/3 of the estimated tax.

ES penalty doesn't have a "reasonable cause" exception for abatement.  But how much are we talking about here?  Example:  your farmer return shows tax due of $24,000.  It was paid March 2, without a return.  Instead, a $16,000 payment could have been made on January 31.  So a month, at 7% annual rate, on $16K is $93.  They don't send notices (at least to nonfarmers) for less than $100.  So it's worth the try.    But how does IRS know that 2/3 of gross income is from farming?  Is there a box to check, other than on the 2210-F?  And if you file that, do you have to pay the penalty even if less than $100?