A Study of Colorado Wheat 
43 
of these figures is lessened by the fact that the sample represent¬ 
ing the nitric nitrogen present just before harvest was taken in 
1913, and the other two in 1914, they still serve to give us a very defi¬ 
nite idea of the rate at which the nitric nitrogen is restored to this 
land after previous removal by a crop, for we can safely assume that 
the crop of 1914 reduced the nitric nitrogen present at harvest time, 
1914, to approximately the same amount that the crop of 1913 had 
reduced it the previous year. The difference between the amounts 
of nitric nitrogen in the fallow land and the cropped land on 4 
December, 1914, gives us the difference of nitric nitrogen in favor 
of the fallowed land. This difference is equal to 243 pounds of 
sodic nitrate. The difference between 299.35 and 101.20 gives us 
an approximation to the difference in the amount of nitric nitrogen 
in the top two feet of soil on 1 August and 4 December; this dif¬ 
ference is equivalent to 198 pounds of sodic nitrate. 
This question was followed more closely in 1915 than in 1913, 
with equally positive results. The cropped land again contained 
its minimum amount of nitric nitrogen about 1 August. On 3 Au¬ 
gust, Section 1800 Red Fife, Check Plot, contained in the surface 
foot the equivalent of 29.3 pounds of sodic nitrate, on 30 August 
42.2, on 22 November 89.1, on 14 December 103 pounds; Section 
1900, Red Fife, Check Plot, contained: On 3 August 19.5 pounds, 
30 August 50.6, 22 November 73.6, 14 December 121.8. An ex¬ 
tended statement of these results is given in tabulated form on a 
previous page, in which the amount of sodic nitrate'corresponding 
to the nit.ric nitrogen found is given both for the surface foot and 
also for the succeeding three feet. This table also exhibits the 
rapid fall of the nitric nitrogen in the cropped land from the mid¬ 
dle of May till the beginning of August, namely, during the growing 
period of the plant. 
The total nitrogen was determined at various times during 
both seasons. The results for 1913 are given on pages 15, 19 and 23 
of Part I, and for 1915 on page 18 of this bulletin. I think it very 
unsafe to attempt any interpretation of the results, owing princi¬ 
pally to the difficulty of obtaining samples of soil which will vary 
by less than the amounts of nitrogen here concerned; for instance, 
an actual increase of ten parts per million in any month would 
mean a percentage difference of one one-thousandth, but this would 
mean, if converted into sodic nit,rate or calculated as proteid mat¬ 
ter, 240 pounds for each four million pounds of soil. We sampled 
150 square feet of soil, taking a core from the center of each square 
foot to a depth of one foot, and it was rarely the case that contigu- 
oue square feet of soil showed so small a difference in total nitrogen 
as 0.001 percent. On the other hand, this difference actually reach¬ 
ed 0.0354 percent, or more than 35 times as much as would have a 
very considerable significance in the development of the crop if 
