890 Journal of Agricultural Research vol. vi, no. 23 



and the elements essential to plant growth. Some soluble constituents 

 will be changed to insoluble and some inorganic to organic. All of these 

 changes must be reflected in the yield of the crop produced. 



This investigation was undertaken to throw more light on some of these 

 changes, especially the influence of manure in the presence of varying 

 quantities of water upon the bacterial activities of the soil, and it may be 

 seen by an examination of the more important literature on the subject 

 that with respect to the control of both manure and moisture this experi- 

 ment is unique. 



HISTORICAL REVIEW 



That the addition of manure to a soil increases the number of bacteria 

 has been shown by Remy 1 (37, p. 660-733) and Fischer (13, p. 358). 

 Caron (6) found that the number of bacteria present depends not only 

 upon the manure added but upon the cultural methods and the crop 

 grown upon the soil. Fabricius and Von Feilitzen (12) found that bac- 

 teria increased in the soil on the addition of manure and that a direct 

 relationship existed between the temperature of a soil and the number of 

 bacteria found in it. That the temperature of the soil is influenced by 

 the addition of manure is shown by Wagner (47), who observed that 

 manure increased the temperature of soil from 1 to 2.8 degrees centigrade, 

 depending on the kind and condition of manure added. Troop (44) noted 

 an average increase of 5 degrees in temperature of soil receiving 25 tons per 

 acre of manure over unmanured soil. Petit (35), however, claimed that, 

 while there was at first an increase in the temperature of manured soils, 

 later it became lower than the unmanured. Stigell (41) concluded that 

 bacteria under favorable conditions for development retarded the 

 conduction of heat in soils and thereby reduced the temperature changes 

 due to the variation in the outside temperature. This in a way might 

 neutralize the effect of manure, for Hecker (20) found that while the 

 temperature of soil to which well-rotted manure had been added was higher 

 than adjacent unmanured soil during the day, the opposite was true dur- 

 ing the night. Grazia (17) stated that manures greatly increase the 

 temperature of the soil. King (26) found that a definite increase in 

 bacterial activity occurred with increased temperature, but that an 

 excessive moisture content greatly reduced the number of bacteria in a 

 soil. Bngberding (11) claimed that manure increased the number of 

 bacteria in a soil, but he considered that the moisture content had a 

 greater influence on numbers than did temperature. That the moisture 

 content greatly influenced bacterial activity was shown by Deherain and 

 Demoussy (9), who found that the bacterial action of a soil was at its 

 maximum when a rich soil contained 17 per cent of water, but that it 

 decreased if the proportion of water fell to 10 per cent or rose to 25 per 



1 Reference is made by number to " Literature cited," p. 923-926. 



