404 ANNUAL REPORT OF THE Off. Doc. 



known that plants take up most of their nitrogen suppl}- from the 

 soil in the form of nitrates; that the soil contains but a small fraction 

 of its nitrogen in that state of combination at any one time, and that 

 the comparatively inert organic nitrogen of the humns is steadily con- 

 verted, during the growing season, by the acid of special organisms — 

 the nitrifying bacteria — into the highly useful nitrates. Without the 

 highest activity of these organisms, the maximum crops can not be 

 grown. The immediate product of the acidity of the nitrifying bac- 

 terium is not, however, a nitrate, but nitric acid; to any considerable 

 excess of this product, or of other acids, in the soil above it, the 

 bacterium is highly sensitive, and when such excess has been pro- 

 duced, ceases its nitrifying activity. To secure the highest result 

 of its working power it is therefore needful that the soil contains 

 an excess of basic material with which the nitric acid can unite, as it 

 is produced, to form a neutral compound. Lime, either as such, or as 

 a carbonate, is most excellent for this purpose; a large excess of 

 caustic lime is however injurious and sometimes fatal to the nitrify- 

 ing organism. Heavy dressings of lime tend, therefore, to stop nitri- 

 ficatiou for a time; in the course of a year or two, the causticity of the 

 lime having been destroyed by chemical action in the soil, nitrifica- 

 tion again sets up with increased vigor. It might appear that nitric 

 acid, being of' powerful nature, could readily seize upon basic mate- 

 1 ial present in the silicates, of which all arable soil are chiefly com- 

 posed, and be thus neutralized, with the accompanying liberation 

 of gelatinous silica, which is not known to exercise seriously inju- 

 rious effects upon vegetation or micro-organiisms; but, in fact, very 

 weak solutions of nitric acid, though effective in their influence upon 

 the nitrifying organisms, are unable to decompose the silicates. In 

 general, therefore, the presence of an oxid or carbonate of the alka- 

 lines or alkaline earth, especially soda, potash, magnesia or lime, 

 is needful to the best nitrification. Soils rich in lime are oftimes 

 deficient in calcium carbonate. F. Polzenick (15) found that one soil, 

 containing 0.546 jjer cent, of lime soluble in 5 per cent, hydrochloric 

 acid, held but 0.014 per cent, in combination as carbonate. This 

 Bmall proportion proved sufficient for the rapid nitrification of bone, 

 but not for that of ammonium sulphate, since the sulphuric acid of 

 this substance is liberated and thus adds to the acidity of the soil. 

 Jenkins and Britton (IG) found, however, that in working with the 

 light soil of Connecticut, large dressings of lime considerably in- 

 creased the availability of the nitrogen of bone, doubtless by a final 

 increase in the rate of its nitrification. 



Not only does lime aid, sooner or later, in the process of nitrifica- 

 tion; it also greatly increased the rate of destruction of organic mat- 



(15) Jahresbincht f. Agrik-Chem. , 1S98, 105. 



(16) Rep. Conn. Agr. Exp. Sta., 1899. Xll-216. 



