BASIC CONSIDERATIONS


 Results from site-specific trials should define a
limited range of alternatives to be evaluated regionally
before a technology can be passed on for farmer-managed
trials.
 When designing site-specific trials it is important
to keep the recommendation domain concept in mind in order
to make the resulting data usable for regional
interpretation. For example, all site-specific trials in
one recommendation domain should have equal treatments,
replications, and plot size. This allows researchers to
combine data for regional interpretation (see next
chapter).

Plot Size

 Plot size must be adequate to achieve trial
requirements. While requirements vary from trial to
trial, the size of experimental units must both fulfill
research requirements and be adapted to practical
circumstances. What is desirable must also be in balance
with what is possible; common sense must guide the team's
work.
 It is important for the number of replications to be
the same with large or small plots. There is a tendency
to believe that larger experimental units make "better"
trials and therefore fewer replications are needed. This
is not true. Larger plots will increase the cost of
trials and they will also increase the probability of a
larger experimental error due to heterogeneity within the
blocks. In general, plot size will be limited by the
amount of land available for the trial on the farm and by
the amount of labor or inputs of other resources available
during the experiment.

Variety Evaluation

 Testing improved genetic material is common for
research in farmers' fields. The following five
considerations are important in variety testing: