10 Nebraska Agricultural Exp. Station, Research Bui. 13 
3.84 per cent as compared with 5.18 per cent for plats 16 
rods by 16.5 feet. 
22. Two hundred uniformly planted thirtieth-acre Kher- 
son oats plats were arranged in 50 groups of four adjacent 
plats each, and also in 50 groups of four systematically dis- 
tributed plats. For both methods of grouping, the ''prob- 
able error" has been calculated for the mean yield of each 
group of four plats. The results indicate that a small prob- 
able error cannot be regarded as sufficient reason for con- 
fidence in the reliability of data. Because of chance groupings 
of either large or small variations where relatively small 
numbers are used, a mean may be either more or less accurate 
than an application of the probable error would indicate. 
23. In four comparative rate-planting yield tests with 
small grains in alternating single-row plats the probable 
error was less than 2 per cent in all cases, and yet there 
existed an average actual error of 34 per cent in relative 
yields due to plat competition. Similar results are indicated 
for variety tests with small grains. 
24. An application of the probable error to tests made 
in 1916 concerning the relative water requirement for grain 
production of Hogue's Yellow Dent corn and Turkey Red 
winter wheat may result in greatly misplaced confidence. We 
may be confident from one test that Hogue's Yellow Dent 
corn uses considerably less water per pound of grain than 
does Turkey Red wheat, and from another test we may be 
equally confident that the corn uses more than twice as much 
water for grain production as does the wheat. The second 
comparative figures are unreliable because the soil was rela- 
tively overcropped by the corn. 
25. Crop tests are subject to such a multitude of local 
environmental influences that errors in them cannot be 
regarded as occurring according to the formulas or rules of 
chance calculated mathematically from purely mechanical 
observations. The probable error may apply where only 
accidental variations occur but not where systematic varia- 
tions exist. Crop tests are subject to systematic variations. 
26. In view of the precautions necessary to guard against 
the invalidating influences of various sources of experimental 
error, greater and better facilities should be provided experi- 
ment stations for the conduct of crop investigations. 
