20 
Colorado Experiment Station 
The results of 1915 agree very closely with those obtained in 
1913 showing that the total nitrogen falls, practically, to a con¬ 
stant at a depth of three feet. This was not the case with the nitric 
nitrogen, as is shown by the samples taken 29 April, 1913, to a depth 
of 12 feet. The distribution of nitric nitrogen in these wms very 
erratic. (See Part I (Colorado Bulletin 208) p. 20). It is quite com¬ 
mon in our samples to find that the fourth foot contains less than 
one-tenth as much nitric nitrogen as the first foot, but it may con¬ 
tain as much or more, or again it may contain no nitric nitrogen. 
It has been intimated that we have considered the difficulty in 
obtaining samples on different dates, that would have been the same, 
had the samples been taken on the same date. This difficulty is real 
and is well shown by the results obtained with 150 samples taken 
from as many contiguous square feet. These results are given in Part 
I (Colorado Bulletin 208) p. 26, where we find a difference of 354 
pounds of nitrogen in the surface foot. This difference is even 
larger than that found for the plot sampled on 13 May and 1 Sep¬ 
tember, 1915, before and after the crop had been grown. This dif¬ 
ficulty is not to be avoided in the case of field experiments. Re¬ 
course must be had to other methods of experimentation which was 
contemplated from the beginning of this work. 
We have now given the weather conditions, the moisture in the 
soil, the nitric and total nitrogen in the soil for 1915, and compared 
these factors with the results for 1913. The two seasons were whol¬ 
ly unlike; the principal differences w^ere that the temperature in 
1915 was lower, and there was about twice the amount of rainfall. 
Its distribution was much more general than in 1913, when over 
two-thirds of the total for the growing season, 6.77 inches, fell in 
May and July. In 1913 the rainfall for July was confined to a period 
of not more than 12 days, including several on which either no 
rain or only a very small amount fell. The total water, rainfall and 
irrigation, received during the two seasons, was essentially the same, 
about 19 inches. The moisture in the soil samples taken in 1915 
was a little higher, the average being between one and two percent. 
The effects of these weather conditions on the amount of the ni¬ 
trates in fallow land, taken to a depth of four feet, were small. The 
maximum difference was equivalent to 13 pounds of sodic nitrate in 
the top four feet. The more even distribution of the water received 
by the land in 1915 brought about a different distribution of the ni¬ 
trates, but we have no proof that they were removed beyond the 
feeding area of the plants, which we assume may extend in this soil, 
to a depth of four feet. There is no indication that the dilution of 
the nitrates in the soil was such as to affect in any way the growth 
of the crop. This last statement does not include any reference to 
the composition of the crop. 
