Thinning border rows differentially affects hybrids in corn yield trials

Border rows are used in yield trials to negate the effect of neighboring plots. Border rows are often not thinned to a final stand as are the harvest rows and it is assumed differential density in the border rows has a trivial effect on harvest row yield. In this study, 10 corn (Zea mays L.) hybrids were planted in 1994, 1995, and 1996 at Urbana, IL, in a randomized complete block design with 10 replications. Experimental units were four row plots with the middle two harvest rows thinned to a final stand of 68 000 plants/ha while the outer two border rows were either thinned as the harvest rows or not thinned. Seed weight (g/100 seed) was significantly and negatively correlated with plants per row (R = -0.57, P > |R| = 0.0001) and significantly and positively correlated with grain yield (R = 0.16, P > |R| = 0.0062). Thinning border rows increased mean grain yield 0.2 Mg/ha and a significant hybrid x treatment interaction was detected. Thinning of border rows decreased the mean square error as much as 26%. Thinning of border rows affected the membership of the highest yielding (elite) group. This is particularly important because it is among this elite group that new hybrids are chosen. We conclude that both border rows and harvest rows should be thinned to a uniform final stand in corn yield trials and failure to do so may result in erroneous conclusions and wrong decisions.