Plat Competition as a Source of Error in Crop Tests 1

̄ That a rather keen competition for soil moisture and nutrients is likely to exist between plants differing in growth habit when grown in close proximity is a well recognized principle in ecology. Investigations conducted at the Nebraska Agricultural Experiment Station indicate that this element of competition is a greater source of experimental error in crop tests than is commonly appreciated. This source of error occurs most extensively in small grain nursery row tests and in 1-row or 2-row corn test plats, in which two sorts are grown Side by side. Its most exaggerated case is, perhaps, the te~ting within a single hill of several corn types differing markedly in growth characteristics. ]Errors resulting from such plat competition appear to be fully as pronounced in many cases as are the errors resulting from soil and other envirbnmental variations, ’ remedies for which have long been sought in the Use of check plats and in replication. This effect of competition is a hidden error which cannot be corrected and should be avoided by supplying, proper experimental conditions. The general conclusion relative to comparative yield tests to be drawn ftom these investigations is that any crop being tested should be .surrounded by a Crop of its own kind in order to avoid the effect of competition with a dissimilar crop, for moisture, nutrients, and possibly light. The principles brought out in these tests concerning plat competition should be applicable to any yield test in which dissimilar crops are being compared. This may be accomplished for all practical purposes by substituting plats containing three or more rows for single row plats and then discarding from the yield test the outer rows which are subject to competition with the adjoining plats. In case of wide field plats, discarding the outer rows is not so important since the percentage error for the entire plat caused by competition would be much lower. The degree of error resulting from such