Date of this Version
It is apparent that many sources of error have unconsciously entered into comparative crop yield tests. The very important matter of overcoming variation in soil conditions as a source of experimental error has been quite extensively studied and reported by various investigators during the past decade. The means suggested for reducing such error have been (1) repetition of plats and (2) correction of yields according to check plats planted to a uniform variety or treatment at stated intervals. Both methods have proved of value and a combination of both may often be used advantageously. Some danger always exists of error occurring in the check plats and that correcting according to them may introduce new errors in the yields of crops compared. The method should, for this reason, be used with caution. Studies in experimental error conducted at this Experiment Station prior to 1911 have been published by Prof. E. G. Montgomery, now of Cornell University, in Bulletin No. 269, of the Bureau of Plant Industry, U. S. Department of Agriculture, and in the Twenty-sixth Annual Report of the Nebraska Agricultural Experiment Station. These published results concern primarily the general problems of repetition and size of nursery small grain plats, and the use of check plats.
The object of the following investigations was to secure further information regarding the elimination of error in comparative yield tests. Shortage of facilities for carrying on this character of work in addition to the regular crop investigations of the Experiment Station has in some cases necessitated intermittent experiments. The duration of some of the tests has for the same reason been shorter than would have been desired.
The author wishes to take this opportunity to thank Professors R. J. Pool and W. W. Burr for the interest and advice they have given him in the preparation of this bulletin as a thesis for the degree of Doctor of Philosophy.