Understanding the continuous corn yield penalty

Seed Daily via SPX: As escalating corn prices have encouraged many farmers to switch to growing corn continuously, they wonder why they have been seeing unusually high yield reductions over the past several years. The University of Illinois conducted a six-year study that identified three key factors affecting yield in continuous corn (CC) systems.

"Prior to this study, the most common management recommendations for continuous corn production were to apply an additional 45 pounds of nitrogen per acre and reserve your best crop land for it," said U of I soil scientist and lead author Laura Gentry. "Very little was known about the agents or mechanisms causing reduced yields in continuous corn systems."

Although corn can be cropped continuously, it is widely accepted that there is a yield reduction compared to corn rotated with soybean (CS). This difference is referred to as the continuous corn yield penalty (CCYP), which is generally in the range of 20 to 30 bushels per acre. The 2012 growing season marked the third consecutive year of unusually high CCYP values in the U.S. Midwest, often with corn yields that were 30 to 50 bushels per acre less than corn following soybean.

…The researchers found that the best predictor of the CCYP was unfertilized CC yield. In years when unfertilized CC yields were relatively high, the yield penalty was low, and vice versa. Unfertilized CC yield is an indicator of how much N the soil is supplying to the corn crop, either from residual fertilizer N or from decomposition of previous crop residues and other organic matter (N mineralization)….

An Ohio corn field, shot by Graylight, Wikimedia Commons via Flickr, under the Creative Commons Attribution 2.0 Generic license