Rap -

The farmer may deplete the field, but it's something that can be restored, and the farmer gets to deduct the cost of the fertilizer and the fuel to spread it with - because it's a cost of doing business that has to be deducted from his gross income in order to come up with what he actually has left to pay his taxes with.

He also can deduct (depreciate) the tractor to plow the cow manure back into the fields if he wants a more organic fertilizer.

"Simplifying the calculations" of costs vs gross income to come up with the net/taxable income is inherently unfair if the business itself is in any way more complex that slitting the envelope to read your paycheck. If you can't handle the tax return - or hire someone competent to help you - then you shouldn't be in business. And it's only fair that the help you hire to get the tax return done should be, and is, deductible as a cost of doing business, even if your only business is spending the check you pull out of the envelope every week or so.

John