Experimental Error in Crop Tests 
45 
ence in yield for the groups may be assigned primarily 
to the differences in stand. During the four years, consid- 
ering three plants per hill a 100 per cent stand, stands aver- 
aging 92.8, 87.2, 82.7, 77.8, 73.1, 66.6, and 43.G per cent 
yielded respectively 85.5, 88.1, 83.5, 82.2, 77.9, 74.8, and 56.7 
bushels per acre. 
It appears from these results that what was regarded a 
perfect stand, namely three plants per hill, was too thick for 
a maximum yield with this variety, since an 87.2 per cent 
stand outyielded a 92.8 per cent stand. The yield by no means 
decreased in proportion to the stand. An average stand of 
43 per cent yielded 66.3 per cent as much as a 92.8 per cent 
stand. It would appear unreliable to correct yields upon a 
basis of stand. 
The yield of an individual row plat planted at a given 
rate will vary greatly according to the stand in adjacent 
rows. For this reason the data in Table 22 must not be 
regarded as necessarily indicating the true relative yields, 
during the years tested, for the different stands as would 
be obtained in a proper rate-of-planting test. 
Because of the chance variations in stand of single-row 
plats, no reliable formulas can be established for the correc- 
tion of yields according to the per cent stand. For example, 
very different results may be expected from a row with 75 
per cent stand, according to whether it falls between rows 
having a 50 per cent or a 100 per cent stand. This is borne 
out by the rate-of-planting tests in rows and blocks during 
the three years 1914-1916 (Tables 11, 12, and 13). 
co:mbination of rate-planting and variety yield tests 
It has been a rather common practice in variety yield 
tests to plant all varieties at one arbitrary ''standard" rate, 
regardless of their growth habits. 
During 1907 and 1908, three varieties were tested at five 
different rates of planting. The Pride of the North and 
Calico, which are respectively small and medium-sized vari- 
eties, increased regularly in yield with the rate of planting, 
and produced their maximum at the rate of five plants per 
hill. On the other hand. Mammoth White Pearl, which is _a 
large late corn, yielded its maximum at the three-rate and 
then fell off sharply. 
