A Second Set of Treatments in a Youden Square Design

Abstract

(i) The field problem. An orchard of Worcester Pearmain apples at Long Ashton (six rows of five trees each) was used in a pathology spray trial of six treatments laid out as a 6 X 5 Youden square. The rows were interspersed with trees of another variety, so that singletree experimental units could safely be used. Most of the treatments were less effective than the standard included, none produced visible damage to the trees, and so it was required to use the same trees in the following season for a different trial, incorporating five treatments. Row-and-column elimination of tree differences was known to be an advantage on this site. Thus, had it been assumed that no residual effects remained from the first trial, a 5 X 5 latin square with a column added would have been the obvious design to choose. However, some of the original treatments had been new compounds, and the first trial had included an untreated control; a design which provided six replicates of five treatments and also allowed residual effects to be examined was therefore felt to be superior. Interactions were not expected between the two sets of treatments, and it proved possible (in this case by trial and error) to construct the following design: