PRACTICAL FIELD ADVICE

 A practical method of adjusting plot yield
 values for missing plants is to harvest only those
 plants that have full competition, then calculate
 the appropriate area for that number of plants and
 adjust for normal plot size. This can work for
 crops such as maize or for many vegetables, where
 individual plants are easily distinguished and
 harvested and for which a specified number of
 plants is expected in a full plot. For example,
 if 25 plants should be in a plot and only 18 are
 found with complete competition, then the yield
 for these 18 can be increased by multiplying by a
 factor of 25/18 to get the estimated yield for the
 full plot, had it not been damaged by outside
 causes. An alternative method for crops which are
 not so easily separated into individual plants, or
 for which plant numbers are not calculated for the
 plot (such as wheat), is to locate small areas in
 the plot which have not been damaged and harvest
 them, leaving an unharvested boundary. Then the
 total area harvested can be adjusted to the size
 of the normal plot and yield adjusted accordingly.
 In both of these cases, the implicit assumption is
 that the parts of the plot harvested were
 representative of the whole plot, a possible
 source of increased experimental error. However,
 this reduces the calculations which are necessary
 for more sophisticated adjustments.

 If correction needs to be made, by no means should a
direct relationship of the average weight of all remaining
plants be used as the estimate. Those plants,
individually, would have higher than normal production
because of a lack of nearby competitive plants.

 Analysis of covariance. A more complete and accepted
method to standardize plant population is through the
analysis of covariance of plot weights and number of
plants reported. The following explanation and example
illustrate the use of this method.
 The analysis of covariance is a statistical method
that allows valid treatment comparisons using observations