1) Control treatments should include the recommended
variety for the region as well as one or more local
materials used by farmers. Comparison of experimental
varieties against these standards helps to make more
meaningful recommendations. The on-farm researcher will
not be interested in identifying only the highest-yielding
cultivar, but will also be interested in other agronomic
characteristics of interest to the farmer.

 2) The farmers' own agronomic practices should be
strongly respected. The main objective of on-farm
evaluation of new varieties is to know their real
potential under farmers' conditions. Therefore special
"experiment station" handling of these trials should be
avoided.

 3) Experimental varieties selected for testing
should include all available alternatives with a
theoretical potential of excellence. This means that not
only the experimental varieties of the official research
sector should be tested along with local materials, but
also varieties from private research programs and from
national or international centers and seed companies
should be considered.

 4) Randomized complete blocks is the experimental
design most often appropriate for these types of
experiments.

 5) The experimental unit should be protected from
environmental bias coming from growth habitsof neighboring
varieties. In maize, for example, where varieties may
differ widely in plant size, extra rows of the same
variety at each side of the experimental unit should be
added. Those border rows are not harvested for
experimental purposes. A common practice in maize is to
plant four rows of each variety but only use the inside
two rows to constitute the experimental unit.

Crop Associations

 A common practice among small farmers is to grow two
or more crops in the same area. Different crop
combinations, row spacing, management, and planting