You need to convert the barter to a USD dollar value
The barter is two transactions, with a USD dollar value that is reasonable. Suppose you trade $200 (reasonably) worth of computer services for $200 in vegetables. IRS treats that as you selling of computer services for $200, and you buying vegetables for $200.
The barter is then business income for both sides, however, you get to deduct the cost of goods sold and other business expenses. So for instance:
- the computer assistance valuates to $200, but as part of that was an "internet router" which cost you $75, so that comes right off immediately, and we're down to $125 gross profit for that transaction. At the end of the year, these are added up, and then business expenses are subtracted - e.g. tools of the trade like a tablet, Safari membership, etc.
- The farmer must declare $200 in income, but they too have business expenses. If you read the IRS literature in depth, you'll see where "farms" are the only business allowed to lose money year after year after year. (have business expenses exceeding their income). So if the farmer takes a loss for the year and pays $0 tax, IRS will not be surprised.
Note that you never have to actually handle USD in any of your transactions. If you want to do everything in barter or Bitcoin, have a field day - actually Bitcoin is a great choice because it's easy to denominate that to USD, because Bitcoin has a published and well known value in USD at the time of the sale.
To raise income to pay tax, sell something for USD
Really, a person could have the exact same problem if all their transactions were barters for "Bitcoin" because there is no difference between a vegetable and a Bitcoin in the view of the IRS. Bitcoin isn't legally a currency, it's a security.
So at some point, you will have to have some transactions that convert to USD, in order to raise the USD needed to pay the tax.
Keep in mind that you get to use "cost of good sold". Remember those vegetables? A far as the IRS was concerned, you paid $200 for them. So if you re-sell those vegetables for $200 USD, you get to subtract that CoGS, so your net profit is $0, and that is a no-tax situation.
As others noted, low income earners pay zero tax, and again, CoGS and business expenses work in your favor. You could live in a shotgun shack right next to a bright, modern well-equipped mechanic's garage where you're doing $2 million USD a year of commercial work - as long as the earnings are largely consumed by business expenses, and your net taxable income is under the minimums.
Further, if you really get into pushing and shoving, you can stay 100% USD-free by negotiating to pay the IRS in some other sort of other security that is acceptable to them. Or, much better option, you can "third-party" the deal by bringing that security to your accountant, and letting them handle the dirty dollars.