A Study of Colorado Wheat 
2 5 
differences in percentages often have a significance, but our meth¬ 
ods and operations are not so perfect that we are justified in attach¬ 
ing too much significance to differences that are, perhaps, no 1 greater 
than our errors. The total nitrogen does not show sufficient differ¬ 
ences to justify us in attaching much importance to them, but the 
percentages of moisture and the quantities of nitric nitrogen do 
justify such inferences as have been presented. 
The question of how great variations may be found in a series 
of samples taken at very small distances apart has been considered. 
To put the question to a practical test, we selected an apparently uni¬ 
form plot, 5 feet by 30 feet, and laid it off in 150 equal squares and 
took a sample to a depth of one foot from the center of each square. 
We have six blocks, each five feet square, which gives us twenty- 
five samples in a block. The total and nitric nitrogen was deter¬ 
mined in each of these samples, which were taken 19 May, 1913. 
The results are shown in the table on the next page. 
The smallest amount of total nitrogen found was 0.11016 per¬ 
cent, Sample 8, Block 6. One sample in Block 1 and two samples 
in Block 4 also' contained this amount. The largest amount found 
was 0.14552 percent. This was in sample 13, Block 6, so that we 
have the minimum and maximum in adjacent areas one foot square. 
This difference amounts to 354.4 parts of nitrogen per million. The 
significance of this amount of nitrogen at a given time will depend 
upon the character of the compounds of which it forms a part. The 
amount of organic matter that it represents may be readily seen 
from the following: Nitrogen forms approximately one-sixth of 
proteid matter and an acre-foot of soil weighs about four million 
pounds. These factors give us for the nitrogenous organic matter 
corresponding to the difference found for the total nitrogen in these 
samples, four and one-quarter tons, or the equivalent of about seven 
tons of dried blood of average grade. 
The difference for the average of the nitric nitrogen in twenty- 
four samples from Block 1, and twenty-five samples in Block 6, is 
1.8 p.p.rn. This may seem a small difference, but it is actually a 
larger amount than we sometimes find in cropped soils taken to the 
same depth. 
The maximum variation in the nitric nitrogen found within this 
area, five feet by thirty feet, is from 5.44 to 14.18 p.p.m., a differ¬ 
ence of 8.6 p.p.m., or a difference equivalent to 206 pounds of sodic 
nitrate per acre-foot of soil. 
We also determined the variation in the amounts of phosphoric 
acid and potash within this area; but we reduced the number of 
samples to four from each five-foot square. The choice was arbi¬ 
trary, but the same for each of the six blocks, in which the first. 
