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Design of Experiments in Growth Chambers — Uniformity Trials in the North Carolina State University Phytotron¹

Experiments conducted in growth chambers frequently are deficient with respect to one or more aspects of experimental design, primarily, proper use of randomization and replication. To provide information with which to counter the usual arguments associated with the failure to use proper designs and to improve the efficiency of growth chamber experiments, extensive uniformity trials (using soybeans) were conducted in the North Carolina State University Phytrotron in three sizes of chambers.

The results confirmed the existence of sizeable, patterned plantto-plant variation within chambers and among chambers of all sizes. Patterns of plant growth within chambers tended to be characteristic of chamber type and to persist over time. Both chamber and time effects were very important.

Correlations among spatially related observations confirmed the potential for serious bias in estimates of both treatment effects and experimental error in experiments which ignore either randomization or proper replication. Properly designed experiments are as important in growth chambers as in greenhouse or field experiments. Proper blocking both within chambers (for within-chamber experiments) and with respect to time and/or chambers (for between-chamber experiments) appears to be effective in controlling a major portion of the variation.

Key Words: Experimental design • Uniformity trials • Randomization • True replication • Growth chamber studies • Intraclass correlations

² Research assistant, presently senior research officer, Malaysian Agricultural Research and Development Institute, Serdang, Selangor, West Malaysia, and professor of statistics, North Carolina State Univ., Raleigh, N.C.

Received for publication August 10, 1981.