DECOMPOSITION OF ORGANIC MATTER IN THE SOIL 329 



The medium subsequently employed by him consisted of silica jelly 

 properly supplied with inorganic nutrient salts. After him other in- 

 vestigators proved that agar, deprived of its soluble organic matter, 

 gypsum and sandstone disks, filter-paper pads, etc., could be used 

 effectively as solid media. 



Nitrous and Nitric Bacteria. — Winogradski's investigations led to 

 the conclusion, foreshadowed by the earlier work of the Franklands and 

 Warington, that the oxidation of ammonia proceeds in two stages, viz., 



(i) 2NH3 + 3O2 = 2HNO2 + 2H2O 



(2) 2HNO2 + 02 = 2HNO3 



The organisms oxidizing ammonia to nitrites, and designated as 

 nitrous or nitrite bacteria, were called by Winogradski Nitrosomonas 

 and Nitrosococcus. The former include species or varieties isolated 

 from soils in Europe, Asia and Africa, and the latter those isolated from 

 soils in America and Australia. The organisms oxidizing nitrites to 

 nitrates and known as nitric or nitrate bacteria, were included by 

 Winogradski in the genus Nitrobacter. 



Apart from these bacteria there is an organism, according to Kaserer, 

 that can oxidize ammonia directly to nitrate. He named it B. nitrator. 

 The reaction is illustrated by the following equation: 



NH3 + H2CO3 + 02 = HNO3 + H2O + CH2O - 41 Cal. 

 CH2O + 02 = H2CO3 + 132 Cal. 



Enough energy for the completion of the reaction is obtained by the 

 oxidation of the formaldehyde (CH2O). Beyond the preliminary 

 announcement of Kaserer's there are no experimental data to prove 

 the existence of this organism, even though other evidence of an 

 indirect nature may be construed to lend support to his theory. 

 But whether it be proved or not that ammonia may be oxidized 

 to nitrate by a single species, it is evident that the number of species 

 concerned in nitrate production is relatively small. 



Relation to Environment. — The conditions that affect nitrate forma- 

 tion in soils may be classified under the following heads: {a) supply of 

 oxygen; (6) range of prevailing temperatures; (c) amount and dis- 

 tribution of moisture; {d) quantity of lime and of other basic materials; 

 {e) quantity of soluble mineral salts; (/) character and amount of 



