Hayes and Garber - Cucurbit Breeding

64 BREEDING CROP PLANTS
nating rows show a greater difference than the same varieties
grown in alternating blocks. Perhaps the extreme effect of competition
is shown by different varieties of corn grown in the same
hill.
In the plots consisting of three rows each, grown at the Minnesota
Experiment Station in 1916, a study of competition was
made. When varieties of different heights were grown in adjacent
plots a considerable effect was obtained in the yields of border
rows in the barley and winter wheat nurseries. The effect of
competition has been observed at other experiment stations and
various ways of overcoming its possible vitiating influence have
been suggested.
One. of the easiest and most effective means of eliminating this
source of error is by the use of sufficiently wide borders which are
discarded at harvest.
In the case of plots, consisting of a single
row, it is possible to make the planting plan in such a way as to
minimize effects of competition. The rows should be laid out
north and south and the varieties and strains most nearly alike
in habits of growth should appear side by side. At best this
method can do no more than decrease the error due to competition,
while the elimination of effective borders overcomes competition.
The use of borders necessitates a larger experimental
area and is somewhat more expensive for a given number of
trials.
CLIMATIC VARIATIONS
One other disturbing factor to be considered in conducting plot
tests is variation induced by weather conditions. Its presence
is so obvious to any one who has worked with growing crops that
further comment is hardly necessary.
In a year of deficient rainfall
the varieties best qualified to subsist under a minimum water
supply will yield most. Some seasons are better for the growth
of early maturing varieties than for late ones. An epidemic of a
plant disease like rust may be fostered or hampered by weather
conditions. The question arises, how may errors due to this
source be overcome? Conducting an experiment over a period
of years is the only effective means at the disposal of the investigator.
The strain which fluctuates the least from year to year
and also gives a high average performance is most valuable for
the farmer.