28 Journal of Agricultural Research voi. xvi. No. 2 



Nitrification in soils is dependent upon several different factors, and 

 chemists have not entirely agreed as to the conditions necessary for it 

 to take place. It was early observed that calcareous material was nec- 

 essary for the preparation of niter beds. Thouvenel (4) in 1787 found 

 chalk and carbonate of lime to favor nitrification more than a number of 

 earths and other chemicals. From the accumulated evidence that car- 

 bonate of lime increased nitrate formation and the fact that acid forest 

 soils often contained no nitrates the conclusion was reached by many in- 

 vestigators that nitrification did not take place in an acid soil. In 1891 

 Warington (25, p. 51) said: 



A further condition of nitrification is the presence of a base with which the nitric 

 acid when formed may combine. This condition is quite essential. Nitrification 

 can only take place in a feebly alkaline medium. 



A little later in 1894 Deherain {8) (/>. 360) made the following 

 statements : 



The nitric ferment does not act in an acid medium It is true that nitrifica- 

 tion may go on in soil deficient in lime Moreover, the application of carbonate 



of lime to such soils is very beneficial and increases the production of nitrates. 



NITRATES IN ACID SOILS 



Twenty-two years before Warington {26) stated that nitrification 

 could only "take place in a feebly alkaline medium" Houzeau {12), in 

 1872, reported nitrification in an acid soil. In 1908 Hall, Miller, and 

 Gimingham (iz) found nitrates in an acid soil, but believing that nitrifi- 

 cation could not take place in an acid medium, they atrributed the phe- 

 nomena to the probable presence in the soil of small isolated particles of 

 calcium carbonate. Since 1908 several workers have reported nitrifica- 

 tion in acid soils. In 191 3 Petit {21) found pronounced evidence of such 

 a condition, while the same year Abbott, Conner, and Smalley (/) re- 

 ported the presence of large amounts of nitrates in an excessively acid 

 soil. The water extract of the soil was acid in reaction and contained 

 considerable aluminium. The next year Temple {23) reported nitrifica- 

 tion in acid or nonbasic soils. White {26) in 191 5 from investigations on 

 some unHmed and limed plots at the Pennsylvania Station found that 

 nitrification was very active in many very acid areas. White remarks 

 that— 



These results are entirely contrary to the general belief that nitrification ceases on 

 very acid soils. 



Since nitrification is the result of oxidation reactions and due to bac- 

 teria, it is affected by soil moisture and aeration. Schlosing {8), in 1868, 

 found that rapid loss of nitrates occurred when a moist "humic soil" 

 was kept in an atmosphere of nitrogen gas. Warington (25) in experi- 

 ments at Rothamsted in 1880 found that saturating ordinary soil with 

 water caused it to rapidly lose the nitrates it contained. Kellner {14) 

 in 1891 and Kelley (zj) in 1914 found that flooded rice fields con- 

 tained little or no nitrates. 



