Small farms are less profitable than large-scale farms, on average, and their operator households tend to rely on off-farm income for their livelihood. Generally speaking, farm operator households cannot be characterized as low-income when both farm and off-farm income are considered. Nevertheless, limited-resource farms still exist and account for 3 to 12 percent of family farms, depending on how “limited-resource” is defined.
http://www.ers.usda.gov/Publications/EIB66/