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).
The second predictor of the CCYP, years in CC, was also strongly correlated with the CCYP. CCYP got worse with each additional year in the CC system through the seventh year, when the study was terminated.
This conclusion is at odds with the claims of many Corn Belt farmers who argue that corn yields in CC eventually attain the same level as CS rotations. On average, the CCYP in this study increased by 186 percent from third-year CC to fifth-year CC and 268 percent from third-year CC to seventh-year CC.
"Yield reductions resulting from additional years of continuous corn production mirror the effects of residue accumulation when corn is cropped continuously," said U of I crop physiologist Fred Below, another co-author. "It is well documented that corn residues introduce a host of physical, chemical, and biological effects that negatively influence corn yields."
Effects of accumulated corn residues include reduced soil temperature, increased soil moisture, reduced N fertilizer availability, and production of autotoxic chemicals, all of which can negatively affect growth and future corn crop development.
|Contact: Susan Jongeneel|
University of Illinois College of Agricultural, Consumer and Environmental Sciences