496 ANNUAL REPORT OF THE Off. Doc. 



For the manufacture of most of the commercial products contain- 

 ing nitrogen, nitric acid is used. For example, gun-cottcm is ordinary 

 cotton treated with nitric acid; coHodion is a form of gun-cotton 

 dissolved in alcohol and ether ; nitroglycerine is glycerine treated with 

 nitric acid, Nitric acid is made from sodium nitrate. Sodium nitrate 

 is mined in Chili and is being consumed at the rate of some 2,000,000 

 tons per year. Statisticians tell us that there is not enough to 

 last more than 40 or 50 years longer. In other word::, our commercial 

 products, so useful and even necessary, are almost wholly dependent 

 on this supply of sodium nitrate. Hence, the hue and cry about the 

 nitrogen problem. 



But what we as farmers are particularly interested in, are the 

 sources of agricultural nitrogen which helps make our foods. Di- 

 rectly or indirectly food nitrogen is obtained from crops, and the 

 source of crop nitrogen, then, is our present inquiry. 



Chemicall}' nitrogen is a gas, colorless, ordorless, rather lazy, for 

 it does not combine easily with other elements. It forms four-fifths 

 of the air we breathe. On every acre of the earth's surface there 

 rests 35,000 tons of nitrogen. But only in combination with other 

 elements is nitrogen of any value ; for example in nitroglycerine as a 

 liquid together with carbon, hydrogen, and oxygen ; in sodium nitrate 

 as a solid together with sodium and oxygen. Only as a nitrate, that 

 is in combination with oxygen and some base like sodium or calcium, 

 is nitrogen of use to the ordinary crop plants. 



In the soil, nitrogen occurs as complex organic compounds result- 

 ing from the decay of jdants or animals — as humus, if you will. Bac- 

 teria act on this nitrogen and convert it to the nitrate form with the 

 help of lime or some other base derived from the decomposition of 

 rocks. The crop plants for the most part, when they are plowed under 

 returns to the soil only then nitrogen taken from the soil during 

 their growth. There is no gain in nitrogen. But legumes, clover, 

 alfalfa, peas, beans — have growing on their roots colonies of nitrogen 

 fixing bacteria which can take nitrogen from the air, and make it com- 

 bine with other elements in such a way that the legume plant can 

 make use of it, and by its decomposition furnish available nitrogen to 

 succeeding crops. Estimates based on analyses have shown that in 

 this way there may be added to the soil anywhere from 40 to 200 

 pounds of nitrogen per acre in excess of what may have been present 

 before. This gain in nitrogen is made by merely jdowing under the 

 stubble remaining after a hay crop, or such growth as may have oc- 

 curred after the crop was removed and before the spring plowing. 



This is one of the most important sources of nitrogen for our crop 

 ])lants: Atmospheric nitrogeji made to combine with other elements 

 and added to the soil without any labor other than the planting of 

 the seed, — and the hay is obtained in addition to more than pay 

 for that labor. 



Another source common to every farm is barnyard manure, which 

 is one way of returning to the soil only what has been removed there- 

 from, unless the stock is fed on purchased material v/hich comes from 

 another soil, — a case of robbing Peter to pay Paul. 



The principal sources of agricultural nitrogen is commercial fer- 

 tilizers. In considering these forms, perhaps it would be v/ell to 

 (•Jiyide them into three classes: 



