NITRIFICATION IN ARABLE SOIL. 359 



CONDITIONS NECESSARY TO THE PRODUCTION OF NllTlATES IN THE 



SOIL. 



The foUowiiijj;' are the more iuii)Oitaiit (.'ouditionis: 



Al'riii'ton. — Manifestly iiitrihcation is aii oxidation and, therefore, 

 re(iuires that the soil should be uniformly aerated. If soil is placed in 

 a closed flask provided Avith a tube for drawing- oft" the gas produced, 

 it will be observed after a certain time that the gas contains carbonic 

 acid and nitrogen, and that the nitrates in the soil have disai)j)eared 

 (Schlosing). Maciuenne and the author have observed that the reduc- 

 tion of nitrates in a nonainated soil is due to an anaerobic ferment, 

 which has been determined by Gayon and Dupetit. They observed, 

 further, that the evolution of nitrogen, due to the decomposition of 

 nitrates, was accompanied by formation of protoxid of nitrogen. 



Hionidify. — Schlosing observed more than 25 years ago that the 

 quantity of nitrates formed iu a soil increases with the humidity when 

 this is not sutticient to wet the soil and interfere with the free passage of 

 the air. A kilogram of soil which contains 9.3 per cent humidity pro- 

 duced in a month 157 mg. of nitric acid, and 470 nig. during the same 

 time when the amount of moisture was 20 per cent. 



Temperature. — Nitrification almost ceases at 5^ C, and it begins very 

 slowly in soils which have been frozen. 



In the month of January, 1893, the author collected from exi)eri- 

 Diental i)lats in the garden of the ]\[useum of Paris samples of soil 

 which were exposed to a gentle heat to thaw them. These were pul- 

 verized and sifted, and then exposed to the temperature of the labora- 

 tory, Avhich rose to 15'^ during the day, but fell to 5 or CP during- the 

 night. Nitrification was so slow that 3 weeks after the beginning of 

 the experiment oidy 47 to 6G mg. of nitric nitrogen per kilogram was 

 found, while only 14 days after the commencement of similar experi- 

 ments on soils collected at the end of JVrarch 137 mg. of nitric nitrogen 

 ])er kilogram was found in samples which were kept at ordinary tem- 

 peratures, and 175 mg. in those maintained at 30° C. 



According to Schlosing, the temjierature most favorable to nitrifica- 

 tion isiabout 35° C. At 55° the activity of the ferments is checked. 



The presenec of a salifiahle base. — Boussingault long ago observed 

 that forest soils donotcontain nitrates, and recently Breal has verified 

 this observation by a very rapid and exact method. He jdaced in 

 dishes filled with the soil to be examined small strips of filter paper, 

 the lower ends of which reached to the bottom of the dishes and the 

 upper ends extended above the soil. Sufficient water was added to 

 make the soil moist. The water rose by capillarity in the strips of 

 paper, drawing up any nitrates that might be present. After a few 

 days he cut off the points of the strips and tested for nitrates in them 

 by means of sulphate of diphenylamine, which, in j)resence of these 

 salts, gives an intensely dark-blue coloration. The failure to obtain 

 this coloration made it certain that the soil contained no nitrates, 



