Subsistence farmers grow crops using traditional methods mostly. They're insulated from the fuel costs etc. that generally drive up the cost of production for the big producers.
Subsistence farmers also tend to bring to market a small portion of their crop. The hope is that as food prices rise, the amount each farmer receives for the crop sold will go up to the point where he can start to invest in his equipment to improve the efficiency of his methods, grow more and sell it, and integrate himself into the global economy.
Eventually, this turns poor subsistence farmers into wealthier cash crop farmers.
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