6 
Colorado Experiment Station 
stand of plants, the nitric-nitrogen present is naturally small in quan¬ 
tity, but under other conditions, it is always higher, and often quite 
high, though we are not now speaking of exceptional cases. On 
4 August, 1915, we found, in the top four feet of a fallow plot, 47.4 
pounds of nitrogen in the form of nitrates and 7.2 pounds in a like 
depth of soil planted to wheat. These quantities of nitric-nitrogen are 
equivalent to 284.4 43-2 pounds of sodic nitrate respectively. If 
this were a single or an exceptional instance, it would show only that 
this difference might exist in the amounts of nitric-nitrogen present in 
cropped and fallow land. This, however, is not an exceptional in- 
'^tance, every series of samples taken, 66 in all, shows the same fact. 
It is not held that the crop has used up this amount of nitrogen, but it 
is held that the crop either hindered the formation of nitrates or did 
exhaust them to this extent. The crop certainly did use up nitrates 
])resent in the soil, and also possibly hindered the formation of them. 
If the latter be true it was only a hindrance and not a destruction of 
ihe power of the soil to nitrify, for we have shown that the nitrates 
are rapidly replaced in this soil as soon as the crop is removed. The 
same plot that on 4 August, 1915, showed the presence of nitric nitro¬ 
gen, equivalent to 43.2 pounds of sodic nitrate, showed, on 13 Decem- 
l)er, 1915, taken to the same depth, the equiva^nt of 232.7 pounds, or 
five times as much as on 4 August. Nothing had been added to this 
soil except the wdieat stubble which had been disced into the sur¬ 
face soil. Irrigation was not necessary, as enough rain had fallen to 
keep the soil fairly moist. It is not probable that the wheat stubble 
disced in modified, in any essential way, the process of nitrification, 
for the increase of nitrates in the soil began immediately after the re¬ 
moval of the crop and before the stubble was disced in. There is no 
question about the action of more considerable quantities of decaying 
organic matter upon the processes of fixation and nitrification but in 
this case the quantity did not seem to be sufficient to produce observ¬ 
able results, or obscure in any way the process of nitrification, for our 
samples were not taken close enongh together to establish the rate of 
nitrification from one week to another or to detect variations in this 
rate. 
The quantities of nitrogen thus transformed into nitrates during a 
single season are more than sufficient to justify their consideration in 
connection with our problem. We found in the 2hd, 3rd and 4th foot ' 
of a sample of this soil taken 29 April, 1913, 23.8, 33.8 and 12.9 parts 
nitric-nitrogen per million, respectively. These quantities seem high, 
but we have found in fallow spots in this same land, cultivated to 
fleets, 22, 28, and 35 parts nitric-nitrogen per million in the surface 
portions of the soil. When one bears in mind that the ratio of avail¬ 
able potassium in the land is so high that its specific action on the 
character of the wheat produced is easily recognized in the plumpness 
and color of the kernels, and that the supply of available phosphorus 
