One of the first questions many farmers ask about continuous corn is: Can I get the same corn yields with continuous corn that I can get in a rotation? The answer is yes, but only once in a great while. Research compared continuous corn to a corn/soybean rotation for 14 years at Lexington, Kentucky (see Table 1). During the 14 years of comparison, continuous corn yields beat corn/soybean only twice. Continuous corn did not do any better when compared with other crop rotations. Continuous corn yields beat corn/wheat/double-crop soybean once out of 11 years and corn/forage once out of five years tested. The two years that continuous corn beat corn/soybean had something in common. Both of those years were relatively dry and disease levels were very low but not sure why this would occur. Conversely, 1990, 1992, and 1997 were years with high levels of Diplodia. Those three years were some of the worst years for continuous corn yields when compared to corn yields in other rotations.
The study in Lexington is not the only place where continuous corn yielded less than corn in some type of crop rotation. Continuous corn yielded about 15 bushels per acre less than corn from a corn/soybean rotation at Princeton in 2002. There were no visual differences in disease levels in that experiment.
While the economics may favor continuous corn, the agronomics do not. So, what is a farmer to do? Pest management becomes very critical. The research at Lexington indicates that when disease is not a factor, continuous corn does very well. Farmers with continuous corn will need to be very good managers of weeds, insects and diseases. Other articles in this edition will focus more on pest management in continuous corn. Farmers will also need to factor the historically lower yields of continuous corn into their budgets. When looking at projected yields and contract marketing, the farmer should be aware that yields with continuous corn are historically 5 to 10% lower than corn yields in a rotation.
|Table 1. Crop Rotation Effect on Crop Yield in Lexington, Kentucky.|
|Corn Yield (bu/A)|
|1987||130||116 -14||135 +5||–|
|1988||68||79 +11||97 +29||–|
|1989||141||155 +14||169 +28||–|
|1990||114||142 +28||141 +37||–|
|1991||94||107 +13||108 +14||–|
|1992||147||181 +34||190 +43||183 +36|
|1993||150||157 +7||169 +19||162 +12|
|1994||140||109 -31||135 -5||108 -32|
|1995||145||154 +9||166 +21||168 +23|
|1996||149||158 +9||173 +24||184 +35|
|1997||118||140 +22||151 +33||144 +26|
|1984-1997||125 ±252)||136 ±30||–||–|
|1987-1997||127 ±26||136 ±30||149 ±29||–|
|1992-1997||141 ±12||150 ±24||164 ±19||158 ±29|