I think the problem may be that plots are identically numbered across sites, so that there is still replication at the subject level of plot. Have you tried subject=plot*site? You might also consider whether to specify site as a random effect, rather than as a fixed effect. That all depends on your inference space assumptions about site, and you would need to consider the interactions with site as probable error terms for testing the treatment effects. A third consideration would be defining the subplots as 1 through 4, and then extracting tests about the subplot effect using LSMESTIMATE statements. Hope this triggers some ideas. Steve Denham
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