TYPES OF ON-FARM TRIALS


 Types and numbers of trials are planned for each
recommendation domain previously identified by an initial
characterization of a region. The nature of the problems,
the availability of personnel, and budget considerations
all influence this allocation. Except for exploratory
trials, which can be used at any time to learn about
unknown situations, the other on-farm trials are
sequential, with specific purposes at each stage.

Exploratory Trials

 Exploratory trials are used when little is known
about an area or about possible effects in an area of a
specific type of technology. They can be considered as
complementary to, or part of, characterization and usually
precede site-specific or regional trials. These trials
normally provide more qualitative than quantitative
information about several factors. Frequently, two levels
of each factor are included and few replications are used.
The most common designs are the 2n factorial and plus or
minus trials. Exploratory trials can sometimes be
superimposed on farmers' fields without the necessity of
special preparation of the experimental area.

Site-Specific Trials

 These are similar in design to on-station trials, but
usually fewer treatments are involved. Perhaps as many as
20 to 25 treatments can be included, although this is not
recommended unless a more complex type of design (e.g.,
lattice or Latin square) is used to keep the experimental
error at an acceptable level. Because of the requirement
for intensive researcher management, few of these trials
are normally conducted. The most common design is
randomized complete blocks with four replications.
Analysis of variance (ANOVA) can include site as a source
of variation, and combined analyses can be performed.