Continuation of a Long-Term Copper Fertility Experiment.

Long-term copper fertility research plots were established in 2009. This experiment is a randomized complete block design with four replications and three treatments. The three treatments were different rates of CuSO₄ solutions sprayed on the soil surface with a CO₂ backpack sprayer applied on 22 May, 2009. The three treatments rates were: 0, 11.2, and 22.4 kg Cu ha^-1. Since that time, no further treatments have been applied and the results are the residual effects of this 2009 treatment. Maintenance fertilizer applications through the years have been equally applied to all plots. For the 2018 corn crop, nitrogen fertilizer was soil injected as a urea-ammonium nitrate solution to give 224 kg N ha^-1 as a preplant application. The corn was planted on 24 May, 2018. Standard herbicide and cultivation practices were used. For tissue analysis, the ear leaves were harvested at the milk stage of the kernels on July 28, 2018. No statistical differences were found between treatments for any of the elements in the tissue analysis. Two rows from the center of each plot were hand harvested and the ear corn weighed. The average harvest plant population was 78,825 plants ha^-1. The weights were converted to 15% moisture. The ear corn yields for these three treatments were: 13,805, 16,005, 14,945 kg ha^-1for the 0, 11.2, and 22.4 kg Cu ha^-1treatments. There were no significant yield differences between the treatments at the 0.10 level. The higher yield value of the 11.2 kg Cu ha^-1 is of interest and deserves further study. The coefficient of variation for yield data was very high (19.4%) and further work will try to reduce this variation. Ear counts at harvest showed a significant difference between treatments. The ear number ha^-1 were 73474, 83044, 79957 for the 0, 11.2, and 22.4 kg Cu ha^-1 treatments, respectively.