71 



manganese may be exhausted,* and that soluble alumi- 

 num and iron be found in soils where now, chiefly man- 

 ganese goes into solution. 



The occurrence of soluble manganese in a soil ex- 

 tract is a strong indication of acidity. But not all acid 

 soils contain soluble manganese. From our work, it ap- 

 pears that rapid nitritication, or the use of a fertilizer 

 which is acid in nature, are the chief causes for the solu- 

 bility of this element. Slow nitrification of the relatively 

 inert soil organic matter causes but little development 

 of soluble manganese, as shown by data in Table IX. 

 In neutral soils, soluble manganese is rarely found; 

 and under basic conditions, the writer has never found 

 a trace of this element soluble in water. Soluble man- 

 ganese added to a very acid soil may be quite largely 

 removed by leaching, even after standing for some 

 days. But if calcium carbonate be added to an acid 

 soil, soluble manganese applied is rapidly removed 

 from solution, calcium being found instead. An acid 

 soil so treated in our laboratory contained but a trace 

 of soluble manganese after six days, and none after 

 thirteen days. 



The field work of Skinner and Beid (19) is interest- 

 ing in this connection. On acid soil of the Arlington 

 Farm, an application of 50 pounds per acre of manga- 

 nese sulphate caused decreased yields of wheat corn, 

 cowpeas and potatoes; with rye, variable results 

 were obtained. After continuing the experiment for 

 five years, systematic liming of the soil was begun. 

 When sufTicient lime had been applied to completely 

 counteract the acidity, each crop except potatoes jdeld- 

 ed best on the manganese treated area. In all proba- 

 bility, the decreased yields attributable to the use of 

 manganese sulphate before liming, were due to the 

 fact that this compound remained unchanged in the 

 acid soil, and proved toxic to the crops grown; on the 

 other hand, it is verj^ doubtful if the increased yields 

 obtained after liming should be attributed to manga- 

 nese sulphate as such. With the establishment of bas- 

 ic conditions, the soluble manganese added would verv 

 likely be precipitated in a relatively insoluble condi- 



*As nn avernsc of determinations made on duplicate samples 

 of soil from the plots used in our field work, there were 262.5 

 p. p. m. of Mn., and 51.3 p. p. m. of Ca., soluble in hydrochloric 

 acid, the digestion being made according to the A. 0. A. C. 

 method. 



