CHAPTER XIV. 



THE INFLUENCE OF SALTS ON THE BACTERIAL 

 ACTIVITIES OF THE SOIL. 



SALTS that occur naturally in soils and those applied to them in 

 various operations influence the number, species, and activity of 

 the soil microflora. These factors are in turn reflected by yields 

 obtained. Some substances applied to a soil serve as food for the 

 growing plant; others increase plant growth but not through the 

 direct furnishing of food. This latter effect may be due to a change 

 brought about by the salt on the physical, chemical, or bacterial 

 properties of the soil. The substance may alter the physical proper- 

 ties of the soil to such an extent that the bacterial flora is modified ; 

 this in turn may increase or decrease the crop produced upon the 

 soil. Other substances may react chemically with constituents 

 within the soil and in so doing liberate substances which can be 

 directly utilized by the growing plant. Again, they may^directly 

 modify the microflora and microfauna of the soil both as to numbers 

 and physiological efficiency. In some cases all three changes may 

 be wrought by the same salt. The question, therefore, arises as to 

 what effect this or that fertilizer or soil amendment is going to have 

 upon the bacterial activity of the soil. Furthermore, there are 

 millions of acres of land in arid America which contain varying 

 amounts of soluble salts. Some of these soils contain such large 

 quantities of these so-called "alkalies" that no vegetation is found 

 upon them. Other soils contain only a medium amount of soluble 

 salts and the vegetation is composed chiefly of alkali-resisting plants. 

 Still other soils contain much smaller quantities of soluble salts and 

 they become injurious only when the soil is improperly handled. 

 The reclaiming of the heavily charged soils and the maintaining of 

 the others in a productive condition can be carried on successfully 

 only when we understand the influence of salts upon the growing 

 plants and their action upon the biological, chemical, and physical 

 properties of the soil. 



Calcium Carbonate. Much work has been done to determine the 

 influence of calcium carbonate, especially when applied to acid soils, 

 on the bacterial content and activity of the soil, but the conclusions 

 reached have not always been concordant. Withers and Fraps 

 found that calcium carbonate added to a soil greatly accelerated 

 nitrification and that it is especially desirable that it should be 



