42 
Colorado Experiment Station 
foot seldom showed as much nitric nitrogen as would be equivalent 
to 20 pounds of sodic nitrate per acre-foot. This was a season of 
high rainfall in general, and long periods without any. In 1915, 
with twice the total rainfall, Avhich fell in a succession of light 
rains Avell distributed throughout the season, we have a very differ¬ 
ent distribution of the nitric nitrogen, for we find even the fourth 
foot containing, at the end of June, as high as the equivalent of 48 
pounds of sodic nitrate; but by 3 August, the nitric -nitrogen had 
been used up to such an extent, that the surface foot contained the 
equivalent of only about 20 pounds of sodic nitrate; the minimum 
found in the fourth foot at this time was nil. The nitric nitrogen 
Imd disappeared from all of the plots in the same manner and to 
about the same extent. The amount of nitric nitrogen in the top 
four feet of soil was at all times throughout the season larger in 
1915 than in 1913. This fact was due. in all probability, to 
the different distribution of the moisture. The period of minimum 
nitrates in the soil Avas, in 1915, 3 August, or the beginning of the 
ripening of the grain. The effects of the crop upon the nitric ni¬ 
trogen in the soil Avere checked by cutting out the wheat on a small 
section 20 by 20 feet, and keeping it falloAv throughout the season. 
Samples Avere taken from this falloAv ground, and also from that oc¬ 
cupied by the Avheat plants on 3 August, 1915, to a depth of four 
feet. The nitric nitrogen present in this fallow land to this depth 
Avas equivalent to 285.5 pounds of sodic nitrate; that present in the 
cropped land, to the same depth, Avas equivalent to 46.9 pounds of 
sodic nitrate. The crop, either by preventing the formation of the 
nitrates, or by using them up, had made a difference equal to 238.6 
pounds of sodic nitrate in this depth of soil. 
It Avas shoAvn in Bulletin 178, p. 91, and again by Sackett in 
Bulletin 193. sample No. 75, pp. 24 and 39, that the nitrifying ef- 
fiiciency of this soil is relatively high. In Part I (Bulletin 208), pp. 
20 and 21, I shoAved the differences in the amount of nitric nitrogen 
in land cultivated falloAV during the season, and in that cropped 
to spring Avheat, for samples taken on 4 December, 1914. I also 
gave the amount of nitric nitrogen found in the cropped land on 1 
August. 1913. The average given by three sets of samples, each 
composed of eighteen sub-samples, taken to a depth of nineteen 
inches, corresponds to 542.43 pounds of sodic nitrate per acre for 
the falloAved land. The nitric nitrogen found in one of our check 
plots of Defiance Avheat on 1 August, 1913. taken to a depth of 
tAvo feet, corresponded to 101.20 pounds sodic nitrate per acre. 
This same plot was cropped to Avheat in 1914, the AA^heat was har¬ 
vested 6 August, the land irrigated 28 August, ploAved 14 Novem¬ 
ber, and sampled on 4 December. We found as the average of two 
!!ets of composite samples taken to a depth of nineteen inches, the 
equivalent of 299.35 pounds sodic nitrate per acre. While the value 
