According to a Tufts University case study on how the market fluctuations can increase concentration of control in agriculture, the Real Food Price Index more than doubled between 2006 and 2009 while real US family farm income from farming sources fell by 18% (p.2-3).
FROM THE TUFTS SITE ANNOUNCING THE STUDY: "With the recession, off-farm income has declined dramatically, leaving family farm households worse off than they were earlier when crop prices were low. He (Wise) finds that for 2009 (the most recent year of data available), these family farmers: Had household incomes 28% below 2007 levels and 21% lower than the average for 2000-6, when crop prices were considerably lower. Average earnings from farming were just $19,274, including government payments. Off-farm income continued to sustain the family, providing on average about $35,000, but this represented a decline of 24% from 2007. Net cash farm income was down 18% from the lower price years 2000-6. Farm sales were up 10%, but expenses increased 8%. An $8,000 decline in government payments put these family farm businesses below their net incomes from the earlier period. The largest farms, those with sales over $500,000 per year, accounted for 73% of the net cash income for the U.S. farm sector as a whole. That figure rises to 88% if one includes the relatively small group of 'non-family' farms, those that are incorporated or operate as other types of business. These are the clear winners from high crop prices".
Timothy A. Wise, "Still Waiting for the Farm Boom, Family Farmers Worse Off Despite High Prices," Global Development and Environment Institute, Tufts University, GDAE Policy Bried No. 11-01, March 2011. http://www.ase.tufts.edu/gdae/Pubs/rp/PB11-01FarmIncomeMarch2011.pdf