EXPERIMF.NT STATION BULLETINS. 149 



are decomposed, and the elements of the animal tissue are incorporated into the 

 soil. Manure placed upon the land rots and enriches it. Dead plants decay and 

 become again a part of the earth from which they sprung. All this decay is 

 brought about by micro-oi-ganisms assisted by the elements. The first change that 

 takes place is a breaking down of the complex nitrogenous substances. The 

 albuminous matter is reduced to peptones by certain types of bacteria, and the 

 peptones are reduced to free ammonia and other simple compounds by the same 

 or other types. The starches and sugars meanwhile are undergoing fermentation 

 into various organic acids and gases, as is also the cellulose or woody fiber of 

 plants. Thus the organic matter becomes entirely decomposed, some of the 

 different elements escaping in the form of gases, and others becoming a part of 

 the soil where we shall meet them again later. 



The organisms concerned in these different processes may all be placed among 

 the ammonifiers. The life requirements of this group are of importance as touch- 

 ing some of the common soil operations. 



A series of laboratory experiments demonstrated the advantage of a bountiful 

 air supply. Flask cultures were made in mineral solutions having potassium 

 nitrate for a basis and containing all the other elements necessary for bacterial 

 growth besides some organic matter in the form of peptone. Pour sets of cul- 

 tures were inoculated with organisms found in different soils on the college farm. 

 One set was placed in an atmosphere from which the oxygen had been completely 

 removed; in the second set the flasks were sealed with wax; in the third they were 

 simply plugged with cotton wool; and in the fourth they were thoroughly aerated 

 After eleven days the cultures were tested for decomposition products. The cul- 

 tures which had been kept in an atmosphere devoid of oxygen showed only slight 

 traces of ammonia; while the other cultures all showed ammonia in larger quan- 

 tities, the amount increasing steadily and consistently with the increased amount 

 of oxygen supplied. These results are significant as indicating the effect of the 

 aeration of the compost heap. Manure and litter well packed down so that air is 

 excluded will be much less liable to loss through decomposition and escape of 

 ammonia than that which lies loosely packed, thus affording conditions for such 

 decomposition. 



DENITEIFICATipN. 



There is a process going on in the soil differing from the latter, which results 

 in a direct loss of nitrogen. This is the phenomenon of denitrification, or nitrate 

 destruction. This process is carried on by the denitrifying organisms, which 

 attack the nitrates already formed in the soil, reducing them to nitrites and free 

 ammonia, the fermentation sometimes going still farther to the liberation of free 

 nitrogen. If the soil be abundantly stocked with nitrates, the denitrifying bacteria 

 under favorable conditions would be capable of destroying a considerable por- 

 tion of them. It is claimed by some workers that as high as 75% of the nitrogen 

 applied to the soil in the form of nitrates is lost by this process. The results of 

 recent investigation, however, tend to prove that this estimate is far too high. 

 Research work upon the oxygen requirements point to the conclusion that the 

 denitrifying organisms develop best when oxygen is exchided. From this 

 conclusion, we obtain another clue to the proper handling of the soil and the 

 compost heap. If the soil is allowed to become packed and hardened through lack 

 of cultivation, the air is excluded and one of the conditions favorable to denitrifi- 

 cation is furnished. Again, if the compost heap is packed down the same result 

 follows. But we have seen how probable loss would ensue by leaving the 

 manure loosely compacted. How shall we avoid a loss? 



By drawing out the manure as fast as it is made, and spreading it on the land. 

 The loss from leaching is inconsiderable since much of the organic matter com- 

 posing the manure is insoluble in water; and little decomposition would ensue 

 owing to the dry condition the greater part of the time during the summej* and the 

 low temperature at other seasons of the year. 



ISriTRIFICATION. 



Opposed to the process of nitrogen waste through denitrification is another 

 process going on simultaneously with it in the soil; a synthetic, rather than an 

 analytic process, whereby simple nitrogen compounds are built up into more 



