40 
Colorado Experiment Station 
summary 
The summary includes the facts presented in Part I, with which 
no summary was presented, because we intended to record the re¬ 
sults of another season’s work on the subject dealt with before we 
formulated our conclusions. 
We believe that the fundamental condition in this work is the 
question of food supplied by the soil; the weather conditions are 
important, but accidental. 
The land used for these experiments contains a liberal supply 
of total potash. We found in 1913 that in the top two feet of soil 
there was 101.6 tons of this substance per acre, of which approxi¬ 
mately one ton was available at that time. If, however, Ave base our 
estimate on the hydrochloric acid-soluble potash, we find that there 
Avas over 25 tons available. The citric acid, soluble phosphoric 
acid Avas about 1,400 pounds, that soluble in hydrochloric 
acid, 9,800. The total nitrogen found in the same depth of soil Avas 
8,240 pounds. The amount of plant food Avas considered ample. 
This estimate, however, Avas based not entirely upon analytical re¬ 
sults, but the crops produced by the land Avere also considered. 
The nitrogen, while sufficient, Avas not considered remarkably 
high. It Avas shoAvn that a very considerable portion of this ni¬ 
trogen actually existed in the soil in the form of nitric ni¬ 
trogen at the time of planting. The top tAvo feet contained ni¬ 
tric nitrogen equivalent to 211 pounds of sodic nitrate. The bio¬ 
logical conditions of the soil are such that the conversion of the soil 
nitrogen into nitric nitrogen proceeds rapidly. 
The j)OAver of this soil to fix nitrogen has been discussed in pre- 
Auous publications (Headden. Bulletin 178, p. 89; Sackett, Bulletin 
179, p. 29), in AAffiich it is shoAvn that this factor is a very important 
one, being sufficient to add very considerable quantities of nitrogen 
to the soil annually, provided the conditions be reasonably favor¬ 
able. I may emphasize this fact by giving the results of observa¬ 
tions made on a sample of soil from this tract of land, but not from 
either of the three sections used for these Avheat experiments. The 
sample Avas kept in a large bottle, loosely corked, at the temperature 
of the laboratory. There Avas no opportunity for the soil to ab¬ 
sorb ammonia or nitric fumes. This sample Avas put into the bottle 
just as it Avas brought from the field, except that the clumps Avere 
broken up and the soil made reasonably fine. In 27 days this soil 
gained 4.82 milligrams of nitrogen for each 100 grams of soil, or 48 
parts per million. This soil had nothing added to it, nor Avas it 
treated in any Avay to facilitate this bacterial activity, except that 
it Avas kept in a moderately warm room. This Avas the smallest gain 
observed by myself or Prof. Sackett in samples of this soil. The 
other samples, hoAvcAmr, were incubated and the moisture Avas 
