Sept. 4. 1916 Influence of Barnyard Manure on Soil Bacteria 893 



Many of the cases in which Individuals have reported a disappearance 

 of nitrates in soil are due to synthetic reactions, the nitrates being built 

 up into complex proteins. For Gerlack and Vogel (15) have shown that 

 there are several varieties of bacteria in the soil which have the power 

 of converting ammonia, nitrites, and nitrates into insoluble proteins. 



The processes of ammonification, nitrification, and nitrogen fixation, 

 being due to the action of micro-organisms, are intimately associated 

 with the moisture content of the soil; hence, we find in many cases this 

 is the limiting factor. Guistiniani (16) found in sandy soil that the 

 rapidity of nitrification of ammonium sulphate was directly proportional 

 to the amount of moisture present when this varied from o to 16 per cent. 

 While Roche (38) has shown that irrigation supplying from 15 to 25 per 

 cent of water to a soil furnished the most favorable conditions for nitrifi- 

 cation, Coleman (7) found nitrification most active in a loam soil with a 

 moisture content of 16 per cent. It was greatly retarded when the water 

 content was reduced to 10 per cent or raised to 26 per cent. It is also 

 interesting to note that he found that with a high moisture content solu- 

 ble organic matter became injurious to nitrification. 



The nitrogen-fixing organisms would also be influenced by the water 

 content, as shown by Warmbold (49), who stated that when the water 

 content went below 10 per cent there was no nitrogen fixation and in 

 some cases there was a decided loss of nitrogen. Krainskii (27) said that 

 nitrogen fixation was at its height in soils containing fairly small quan- 

 tities of water. Later he (28) stated that the higher the humus content 

 the larger the water content of the soil required for optimum nitrogen 

 fixation. Increasing the organic matter of the soil was not found to 

 increase nitrogen fixation, although there was an increased bacterial 

 activity. Hanzawa (18) found that the humus of stable manure could 

 be used as a source of energy by some nitrogen-fixing bacteria. 



PLAN OF EXPERIMENT 



The plan of the experiment is such that it can be divided into three 

 parts. The first deals with the bacterial activities of a soil receiving a 

 definite amount of manure and measured quantities of irrigation water 

 and kept fallow in pots under vegetation house conditions. In this the 

 moisture content could be accurately maintained by the weekly weighing 

 and the replacing of lost moisture. The variation in temperature and 

 moisture of this series would not be as great as it would be under field 

 conditions. The second part deals with the bacterial activities going on 

 in a soil under field conditions, the soil receiving known quantities of ma- 

 nure and water but kept fallow. The third part deals with soil of the 

 same field under irrigated conditions and manurial treatment the same 

 as the second part, but producing a crop. 



