332 Microorganisms and Soil Fertility 



the competition of the bacteria for the available nutrients in the soil 

 is repressed by increased acidity. On the other hand, a less acid or 

 shghtly alkahne reaction of the soil may become unfavorable to the 

 development of fungi and have a favorable effect upon many of the 

 soil bacteria. Thus, when conditions are made unfavorable to the 

 development of one group of organisms in the soil, another group 

 may be favored. 



Addition of calcium carbonate to an acid soil was found to stimu- 

 late greatly the multiplication of bacteria, accompanied by an in- 

 crease in the decomposition of the soil organic matter. This is 

 shown in Table 75. Addition of excess calcium carbonate and espe- 



Table 75. Influence of CaCOs on Evolution of CO2 from Soil (from Konig) 



cially of magnesium carbonate, however, may become injurious to 

 many of the soil bacteria. 



Effects of Cultivation and Fertilization 



Cultivation of soil, which results in conservation of the soil mois- 

 ture, is favorable to the development of various groups of micro- 

 organisms. It brings about an increased production of nitrate be- 

 cause of improved soil aeration. By favoring the development of 

 aerobic organisms, cultivation stimulates greater decomposition of 



Table 76. Influence of Tillage upon Abundance of Bacteria in Soil 



(from Chester) 



