I'd venture farmers make half or more more of their money on futures markets. Argi-business is a global market and optimal prices for your commodities don't necessarily conform to your local conditions/crops/etc.

I can't speak for all farmers, but my family owns a farm and the futures market is huge in it generating money.

You can use the futures markets to hedge against bad crop yields, lock in profits for accounting and cash flow purposes, inform what crops you are going to grow. It's immensely valuable.