Previous Corn Hybrid Effect On Yield of Following Corn Hybrid.

Increased demand for corn grain in 2007 and 2008 prompted a large expansion in corn following corn (corn-corn) acreage throughout the US Corn Belt. Yield loss associated with corn-corn is well documented relative to the corn-soybean system, but the causal agents are not well understood. Our research objective is to determine the relationship of the first year hybrid to the yield of the second year hybrid in multiple environments and relative to a corn-soybean system. Research is located at six Iowa State University research farms (three northern farms and three southern farms) and across two growing seasons (2007-2008 and 2008-2009). Three hybrids were arranged as the main plot in 2007 with 12 hybrids arranged in a split-plot design in 2008 on the existing main plots. The 12 hybrids were also placed onto nearby soybean residue at each location to provide a comparison to the corn-corn plots. The same experimental design was also used for the 2008-2009 study except soybean main plots were established amongst the three hybrid main plots. Hybrids for each research farm were chosen based on their relative maturity, disease susceptibility, and genetic background. In 2008, all northern locations were severely damaged by strong winds one week prior to harvest causing harvest loss at those locations. No first year hybrid effect was indicated in a combined location analysis (n=6); however individual analysis of each location did show the first year  hybrid did effect second year hybrid yield at one northern farm. Yield differences occurred among second year hybrids grown in 2008 at four of six farms. Second year hybrid differences indicate that selection of hybrids could affect yield in a corn-corn system. Overall, yield was reduced 8% in the corn-corn system compared to the corn-soybean at the northern farms and 14% at the southern farms.