Over the past 40 years, the U.S. agribusiness sector has experienced a noticeable increase in market concentration in the seed, livestock and food retail markets.

According to a study released earlier this month by the U.S. Department of Agriculture (USDA) called “Concentration and Competition in U.S. Agribusiness,” a few large companies now control most sales in these areas. 

The study found that the two top seed companies now provide seed for about 72% of planted corn acres and 66% of planted soybean acres in the...