ABSTRACT
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 .
