Finding Hidden Treasure: A 28-Year Case Study for Optimizing Experimental Designs.

摘要

Field-based agronomic and genetic research is a decision-based process. Many decisions are required to design, conduct, analyze, and complete any field experiment. While these decisions are critical to the success of any research program, their importance is magnified for research on perennial crops due to multiple years of data collection. The objective of this paper is to summarize 28 years of field-based perennial forage grass research at a single location describing changes to experimental design methodology, illustrating both predicted and empirical results of those changes. The study is based on an analysis of total forage yield for 114 genetic experiments of 11 forage grass species. Over the course of time, plot sizes were reduced from 5.6 to 2.8 to 1.4 m², resulting in a decrease in mean CV from 18.6 to 13.3 to 11.5%, respectively. These changes in precision, directly opposite that predicted from Smith’s Law of Heterogeneity, were attributed largely to a vastly improved relative efficiency of blocking and spatial adjustment as plot size was decreased: 212 vs. 130% relative efficiency of blocking and 240 vs. 109% relative efficiency of spatial adjustment for 1.4 vs. 5.6- m² plots. These changes suggested that spatial variation at this site consists of fine-scale variation that is uneven, unpredictable, and cannot be easily captured by incomplete blocking or spatial analyses of the larger experimental units. Finally, a power analysis was used to predict the number of replicates required to detect expected differences for a series of experiments, resulting in a high level of predictability and a highly successful application of power analysis to assist with the design of field experiments .