EFFECT OF LIMING 217 



uniform distribution of the moisture necessary for the activities 

 of the soil microbes. 



The effect of stirring soil upon the development of bacteria is 

 shown in Table 52. In this investigation the soil was kept at a 

 uniform moisture content and thoroughly stirred at frequent inter- 

 vals. The influence of this treatment was very pronounced, as 

 shown by an increase in numbers of bacteria from about two mil- 

 lions per gram present in the soil initially to over twelve millions, 

 after a period of 24 days. The effect of such mechanical altera- 

 tion of soil is more pronounced with the deeper layers of soil 

 than with the surface soil, since the deeper layers are more imper- 

 fectly aerated in an undisturbed condition. 



TABLE 52 



Influence of Tillage upon Abundance of Bacteria in Soil 



(from Chester) 



T, . , , ^ . Numbers of bac- 



reriod or time , . 



tena per gram 



At start 2,040,000 



After 7 days 5,495,000 



After 9 days 6,171,000 



After 14 days 11,326,000 



After 24 days 12,600,000 



Effect of Liming. — There is no better way of demonstrating 

 the effects of simple soil treatment upon the nature and activities 

 of the microbial population than by examining the effects of lime 

 on an acid soil. Following the addition of lime, the hydrogen-ion 

 concentration of the soil diminishes (the pH increases). The 

 extent of the decrease in acidity depends upon the amount of lime 

 added and upon the nature of the soil. The more lime is added to 

 the soil, the greater is the change in reaction, up to a certain 

 point which is distinctly alkaline, namely, at a pH. of 8.2. Above 

 this point any further addition of lime will exert no effect upon the 

 reaction, as expressed in terms of hydrogen-ion concentration. 



Soils differ in their buffering properties, that is, in their ability 

 to react with considerable amounts of acids or bases without 

 appreciably changing in reaction. To effect a definite change in 

 reaction, a clay soil may require two times as much lime as a loam 

 soil. The greater the buffering action of the soil (combining power 

 with base or acid), the greater is the amount of lime required before 



