151 



some inorganic to organic. All of these changes are reflected in the 

 crop yield. 



Number. That the addition of manure to a soil increases the 

 number of bacteria has been shown by Remy and Fischer. 



Caron found that the number of bacteria present depends not 

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

 crop grown on the soil*. Fabricius and von Feilitzen found that 

 bacteria 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 who 

 observed that manure increased the temperature of soil from 1 to 

 2.8 C., depending on the kind and condition of manure added. 

 Troop noted an average increase of 5 in temperature of soil receiving 

 25 tons an acre of manure over an unmanured soil. Petit, however, 

 claimed that, while there was at first an increase in the temperature 

 of manured soils, later it became lower than the unmanured. Stigell 

 concluded that bacteria under favorable conditions for de relopment 

 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 

 found that although 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 during the night. Grazia 

 stated that manures greatly increase the temperature of the soil. 

 King 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. Engberding 

 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, 

 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 cent. 

 With soils less rich in humus a somewhat higher proportion of water 

 was necessary to retard oxidation to any marked degree. In a 

 manured soil the coarse manure tended to cause the surface soil to 

 dry out, while fine manure prevented evaporation. King observed 

 that manured land contained more moisture throughout the year 

 than unmanured, and this was reflected in both a greater number 

 of bacteria and in a larger crop. The bacteria themselves may 

 play a small part in this difference in moisture content, as was 

 shown by Stigell, who found that bacteria decreased the speed of 

 evaporation of water from Petri dishes. Hiltner and Stormer's 

 results indicate that the addition of manure to a soil brought about 



