DECOMPOSITION OF ORGANIC MATTER IN THE SOIL. 265 



Relation to Environment. Nitrate reduction is favored by insufficient 

 aeration, as well as by an abundance of readily decomposable organic 

 matter. In fine grained, compact soils nitrate formation and nitrate 

 reduction may alternate, depending upon the more .or less complete 

 replacement of soil air by water. Similarly, in soils receiving excessive 

 amounts of animal manure denitrifying bacteria may cause the reduction 

 of nitrates. In green-house soils excessive moisture, as well as excessive 

 amounts of organic matter, may be present and may prevent the accumu- 

 lation of nitrates. It has also been shown by Niklevski that, contrary to 

 opinions previously held, denitrification may occur in manure heaps. In 

 the better aerated surface portion of manure heaps conditions are favor- 

 able for the oxidation of ammonia to nitrites and nitrates. The nitrous 

 acid may combine with ammonia to form ammonium nitrite, the latter 

 decomposing, spontaneously, into water and nitrogen gas. It is very 

 likely, also, that the nitrites and nitrates are reduced by the denitrifying 

 bacteria in manure. On the other hand, in manure kept moist under the 

 feet of cattle nitrite and nitrate formation is prevented and losses by 

 denitrification are not likely to occur. 



The economic significance of denitrification was overestimated at one 

 time, on account, largely, of the assertion of Wagner in 1895 that in all 

 soils receiving applications of horse manure, the nitrates in the soil itself 

 as well as those added in commercial fertilizers are almost certain to be 

 destroyed by denitrification. Subsequent experiments by many _ investi- 

 gators demonstrated that under field conditions, denitrification is a factor 

 of slight moment ; however, in the green-house, in the manure heap (under 

 certain conditions) and in market gardening where manure is used at the 

 rate of 45,359 k g- to 54>43! kg. (50 to 60 tons) per acre, the danger 

 of denitrification is real. 



ANALYTICAL AND SYNTHETICAL REACTIONS. 



AMOUNT or BACTERIAL SUBSTANCE IN THE SOIL. Various decom- 

 position processes in the organic matter of the soil may be designated as 

 analytical in that protein, carbohydrates and fats are split into more 

 simple compounds. At the same time, the microorganisms concerned 

 in the decomposition processes multiply very rapidly and fashion the 

 complex compounds of their cell-substance out of the simple cleavage 

 products in their medium. In other words, analytical and synthetical 

 reactions proceed hand in hand in the soil. 



