144 INFLUENCE OF SALTS ON THE SOIL 



effect due to the manganese salts, but the soil was acid, a condition 

 which may have accounted to a considerable degree for the nature 

 of the results. 



It is suggested that when the action of manganese is beneficial, 

 "it is probably due (1) to the increased oxidation produced in the 

 plant roots whereby the plant is stimulated to greater activity and 

 to increased absorption of the material useful for its growth and 

 general metabolism; (2) to the stimulation of the activity of micro- 

 organisms in the soil; (3) to an increased oxidation within the soil." 



The same authors also suggest that when large applications of 

 manganese have been found to be injurious, the injury is 

 undoubtedly due to the " excessive stimulation and excessive oxida- 

 tion in microorganisms and in the plant, with a resulting change in 

 the biochemical activities of plant and microorganisms and in the 

 conditions of inorganic and organic soil constituents, the ultimate 

 result of which change is injurious to the growing crop." 



Montanan found that manganese carbonate, sulphate, and dioxid 

 greatly stimulated nitrification, but attributed it to either the direct 

 or the indirect furnishing of oxygen to the nitrifying organisms, 

 and not to any catalytic effect of the manganese itself. Beijerinck 

 observes that some soil organisms have the power of oxidizing 

 manganous carbonate. Olaru found that manganese in the propor- 

 tion of one part to 200,000 parts of nutritive media greatly increases 

 nitrogen fixation. He also considers it rather likely that the 

 increased yield obtained after the application of manganese com- 

 pounds to a soil is due to its accelerating the action of the nitrogen- 

 fixing organisms of the soil. 



Leoncini found that the application of manganese oxid to the 

 soil at the rate of 0.035 to 2.2 per cent, favored nitrification, whereas 

 larger amounts had no effect. 



Brown's work, which is probably the most extensive study of the 

 influence of manganese compounds on bacterial activities so far 

 reported, shows that the influence of the manganese salt upon bac- 

 terial activities varies with (1) the kind of salt added manganese 

 chlorid and sulphate acting in low concentrations as stimulants to 

 both ammonifying and nitrifying bacteria, but in greater concentra- 

 tion being highly toxic; (2) its action varies with the specific class 

 of organisms which were being studied, the ammonifiers being more 

 resistant than are the nitrifiers. 



Potassium Salts. Because potassium is essential for the nutrition 

 of both the higher and lower forms of plant life, it is to be expected 

 that when added to a soil medium poor in potassium it^will increase 

 bacterial growth, but, like many other true nutrients, may become 

 toxic if present in too high concentrations. As already noted, 

 Engberding states that potassium sulphate caused a slight increase 

 in the bacterial content of a soil. While Peck found it to increase 



