Hayes and Garber - Cucurbit Breeding

CHAPTER IV
FIELD PLOT TECHNIC
In carrying out crop-breeding studies the number of varieties
and strains has been greatly multiplied. Vilmorin's isolation
principle, whereby the value of any selection is determined by the
breeding nature of the progeny, has been universally adopted.
The field is then the plant-breeder's laboratory and the question
of correct field technic is of the utmost importance.
The difficulties, of making all conditions of similar nature for a
large number of strains or varieties which must be tested, are
very numerous. The method used must be such that the performance
will be a correct indication of the comparative value
of the strains being tested when grown under farming conditions.
The purpose of the present chapter is to discuss field
plot technic for such disturbing factors as soil heterogeneity and
climatic conditions.
The field
SOIL HETEROGENEITY
selected for the comparative trials should be representative
of the soil and climatic conditions under which the crop
will be grown. The land must then be cropped in such a manner
that it is kept in a uniform state of good productivity. In order
to do this, it is necessary to observe some one of the standard
rotations. It is a good practice to have one or more bulk crops
rotated with the breeding plots in order to keep the land uniform.
If only one area of land is available there is then no choice and the
investigator must see that this field is treated in the best possible
way. If more than one field is available, it is possible to determine
which is more nearly uniform by a correlation of contiguously
grouped plots as outlined by Harris (1915).
Harris' Method of Estimating Soil Heterogeneity. By
used as an index
Harris' method the coefficient of correlation is
of soil uniformity This statistical constant measures the degree
.
of correlation between contiguous plots grouped in a certain way.
If the variation in yield from plot to plot is simply due to random
sampling, there will be no correspondence between contiguously
grouped units. On the other hand, if the field is "patchy"
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