The Effect of Soil Heterogeneity and Plot Size on Yield Variability in Corn

The successfulness of an experiment is largely determined by the precision of the results obtained. The precision and the efficiency with which work is done may often be increased by automation. At the present time all irrigation is done in rows across plots by the University of Nebraska corn research program. Planting and harvesting is done by hand because it is impossible to plant or combine across the rows by machine. The plots have been planted across the rows because it was assumed that there was more variation between streams of water than in the direction of irrigation within a replication. If no difference could be attributed to the direction of irrigation, plots could be oriented with the rows and machine harvesting and planting would be feasible. In order to evaluate the practicality of automation, each of the component parts of the program were analyzed in terms of cost functions. Uniformity trials may be used to determine the extent of plot to plot variability and soil heterogeneity. In addition, they may be used to construct contour maps of soil fertility, to estimate the effects of plot size and shape, to study the efficiencies of various experimental designs, and to adjust yields of subsequent experiments conducted on the same plots. Uniformity trials may be conducted using a single variety or by using several varieties and an experimental design which is successful in removing genotypic effects. The success of a uniformity trial is greatly enhanced by the care with which uniform field husbandry is administered (LeClerg, 1962). Soil heterogeneity is an important feature which cannot be easily regulated but can significantly change results in field work. Plot size and shape are dependent on soil heterogeneity and are therefore important considerations in any research program using field plots. It is important to know in what way soil heterogeneity affects experimental results if the most precise data are to be obtained. The purpose of this study was to determine the optimum plot size and shape for corn yield trials conducted under irrigated conditions on the Red Clover field at Lincoln, Nebraska, and to determine if there was any detectable difference in performance caused by the direction of irrigation. A secondary aspect of the experiment was the comparison of different methods of determining optimum plot size. Advisors: Mumm, R. F. (Robert F.) and Compton, W. A