Grain yields decrease when corn (Zea mays L.) follows corn compared to corn grown in rotation with other crops. The factors that decrease grain yield of corn following corn are not well understood, and limit recommendations available to corn growers. Our objectives were to determine (i) if plant population, moisture, and yield of 2^nd year corn are affected by the previous-year corn hybrid, (ii) evaluate if continued use of single hybrid over two growing seasons influences grain yield, and (iii) compare 2^nd year corn yields to corn grown in rotation with soybean. The experiment was conducted at six Iowa locations in 2008 and 2009; three locations were in the Northern region of Iowa and three in the south. Three corn hybrids were planted in 18 m² blocks as the main plots in the first year, followed by 12 hybrids planted on each of the main plots in the second year. The same 12 hybrids were planted into a nearby field on soybean residue at each location in 2008, but established as a main plot for 2009. Plant population was not influenced by the three previous-year corn hybrids. Plant populations were greater when corn followed soybean compared to 2^nd year corn. Grain moisture content was not influenced by crop rotation or previous-year corn hybrid. Previous-year corn residue did not impact grain yield of the current-year hybrid, and the continued use of single hybrid over multiple growing seasons showed no influence on grain yield. Cropping system influenced grain yield in 2009, within both regions. Second-year corn yields were 11% and 14% less in the north and south regions, respectively, compared to corn rotated with soybean. Previous-year corn hybrid did not influence plant population, grain yield, or grain moisture. The influence of previous-year corn hybrid on the root and plant growth of the current-year hybrids is not well understood and may account for the decrease in grain yield. The objectives the second study were to determine (i) if current-year corn grain yields, root, and plant biomass were influenced by previous-year hybrid and/or cropping system (ii) if there are differences in plant and root biomass among modern commercial corn hybrids (iii) if root and plant biomass are correlated with grain yield. In 2008 and 2009, root and plant biomass studies were conducted at two Iowa State University research and demonstration farms. Experimental design and corn hybrids were the same as the grain yield study. At each location, root and plant biomass samplings were conducted at four different sample dates: V4, V12, VT, and R6. After sampling, roots were washed, dried, and weighed while plants were dried and weighed. Root and plant biomass were compiled and calculated for comparison. Overall, previous-year corn hybrid/cropping system did not influence root or plant biomass; however, plant biomass was greater when corn followed soybean compared to 2^nd year corn at Kanawha and Ames in 2009. Current-year hybrids were variable and did not indicate strong differences in root or plant biomass. Root biomass was not correlated with grain yield within any sample date. Plant biomass was correlated with grain yield at sample date 2 and 4 in Kanawha (2009). Root to shoot correlations were strong within all sample dates indicating that root growth is correlated to shoot growth throughout the growing season. Root and plant biomass are not influenced by the previous-year hybrid and are poor indicators of final grain yield.