532 SOILS: PROPERTIES AND MANAGEMENT 



to soils have not afforded as satisfactory results as have 

 the trials with water cultures. Applications of a certain 

 salt of manganese, when applied at the same rates to 

 different soils, have in some cases produced increased 

 growth, have in other cases had no apparent effect, and 

 have in still other cases proved injurious to plants. The 

 reason for this is doubtless to be found in the inherent 

 properties of the particular soil to which the application 

 is made. 



451. Action of manganese as a fertilizer. — The fact 

 that manganese stimulates plant growth in water cultures 

 is very good evidence that it has at least a direct action 

 on the plant. Whether it has a further influence through 

 reactions brought about in the soil is less evident, although 

 it seems likely that such is the case. Thus, Skinner and 

 Sullivan x conclude from some of their experiments that 

 oxidation in some soils is increased by the application of 

 manganese salts. It also seems probable that manganese 

 may have some influence on the activity of the microor- 

 ganisms of the soil, but this has not been definitely demon- 

 strated. 



452. Forms of manganese and response of soils. — 

 The manganese salts that have been found to be effective 

 as fertilizers are the sulfate, the chloride, the nitrate, the 

 carbonate, and the dioxide. Of these the first has been 

 most generally used, and in quantities up to 50 pounds 

 an acre it has in most cases not been toxic. On acid 

 soils it is not supposed to exercise any beneficial action, 

 and on very productive soils Skinner and Sullivan, in 

 the experiments cited above, found it to be ineffective; 



1 Skinner, J. J., and Sullivan, M. X. The Action of Man- 

 ganese in Soils. U. S. D. A., Bui. 42. 1914. 



