On block designs partially balanced for neighboring competition effects

摘要

In agricultural field experiments, there may be situations where in order to control heterogeneity and conserve resources, the treatments are assessed in experiments using small, adjacent units. As a result, the estimates of treatment differences may deviate from the differences shown in larger units because of competition from neighboring units. For example, intervarietal competition may occur in long narrow plots without guards, where the yield of a variety may j be depressed by more aggressive neighboring varieties; spread of an applied treatment such as irrigation, fertilizer, pest control spray, from one plot to surrounding ones. Competition thus occurs when a response to a treatment on one unit is affected by treatments in neighboring units. This competition can contribute to variability in experimental results and lead to substantial losses in efficiency. By properly organizing the experimental material, attempts can be made to minimize and also estimate these competition effects.