Augmented row–column designs for a small number of checks

Augmented designs allow the testing of a large number of unreplicated entries. Replication of interspersed check cultivars according to a blocked design allows estimation of an error variance as well as local control for unreplicated entries. The most commonly used augmented designs use one-way blocking, but extensions have been suggested using blocking in rows and columns. We propose a flexible strategy to generate such designs, which is particularly suitable when the number of check cultivars is small. A salient feature of the approach is a grouping of adjacent rows and columns and the imposition of an additional blocking unit formed by the intersection of row and column groups. These superimposed blocking structures cater for an even distribution of replications for checks across the experimental field. We provide SAS code using the OPTEX procedure to generate such designs and discuss three examples illustrating the flexibility of the approach.