Wade Kent and Roger Elmore
15 Apr 2010
Corn yields suffer when corn follows corn compared to corn grown in rotation with soybean, in most situations. One common misconception is that over time yield will recover within a continuous corn system, but this just isn't the case. Instead, the greatest reduction in corn yield will occur during the first year of corn following corn and remain at that level until the cropping system is changed. Expect a 10% to 15% decline in grain yield when corn follows corn compared to a corn-soybean rotation.
A number of factors are associated with the yield deficit, but none have proven to be the "fix-all" for improving crop yield. This limits recommendations available to corn growers, and creates numerous possibilities as to what is decreasing yield. The question most asked, is whether the hybrid grown in the previous season influences corn yields the following year. Research that addresses this question has not been conducted since the 1980's, reducing our ability to provide solid recommendations for today's corn hybrids and management systems. To better understand this issue, we have conducted research at six Iowa locations, in 2008 and 2009; three locations in the northern half of Iowa and three in the southern half. Our efforts were focused on understanding the influence of the previous-year hybrid on the performance of the second-year corn.
In the second year, twelve hybrids were placed on top of crop residue from three corn hybrids, as well as soybean residue. Triple-stack hybrids, with appropriate relative maturities, were planted in the different regions of the state at 35,000 seeds per acre. Management practices were similar at all locations; soil fertility was maintained at levels that would not limit yield.
Influence on second-year corn: Population and grain moisture
To understand the overall influence of the previous-year hybrid residue on the current-year hybrid, we measured corn population, grain moisture and yield. Plant population did not change due to the type of hybrid grown previously. Plant populations with corn following soybean were greater, however, than those of second-year corn. Seedling loss was greater for second-year corn compared to corn following soybean. However, other research has shown that slightly increasing seeding rates for corn following corn may not increase yield and will not overcome the 10% to 15% yield reduction associated with corn following corn.
Grain moisture of the current-year hybrids was not influenced by the previous-year corn hybrid in any of our trials. In addition, no grain moisture differences were found between second-year corn and corn following soybean. Therefore, grain moisture at harvest is most dependent on the growing season and not related to residue type. In 2008, grain moisture averaged 19% to 20% across the northern and southern regions. Whereas in 2009, four of the six locations had grain moistures greater than 25% at harvest, no matter the rotation. High grain moisture was common across Iowa in 2009, due to the abnormally cool growing season and wet fall.
Previous hybrid does not impact second-year yields
In 2008, second-year corn yielded 10% and 14% less for the northern and southern regions, respectively, when compared to corn following soybean. Similar yield differences were observed in 2009, where second-year corn was 11% and 14% less for northern and southern regions. Although the rotation effect was obvious across the regions, the specific type of corn hybrid residue did not matter. Thus, previous-year corn hybrid should not be a concern when selecting hybrids for the next growing season. We also found that continued use of the same hybrid over multiple growing seasons did not decrease grain yield more than occurred with rotated hybrids.
Based on the results, previous-year hybrids do not influence plant population, grain moisture or yield in second-year corn. These results seem to eliminate another possible factor (hybrid grown previously) as a variable that might explain the yield reduction that occurs when corn follows corn. When selecting hybrids to plant for the current growing season for corn following corn, we do not see a reason that the hybrid grown previously should impact your choice in the second year. Nevertheless, you should expect yields to decrease by 10% to 15% in continuous corn compared to corn grown in rotation with soybean.