ACTION" OF MANGANESE IN SOILS. 29 



has been 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 microorganisms of the soil; (3) to an increased oxidation within 

 the soil. In this connection it is of interest to note that Robin and 

 Bardet 1 . concluded that colloidal metals, especially manganese, pro- 

 mote oxidation in the tissues of animals and intensify metabolism. 



Where manganese has been of little value or has given decreased 

 yields, conditions were such that stimulating actions on plant and 

 microorganisms did not come into play, or, on account of the acid 

 reaction of the soil, the effect of the stimulation led to reduction 

 processes being predominant. Large applications of manganese 

 have been found injurious, undoubtedly because of excessive stim- 

 ulation and excessive oxidation 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. 



Soils poor in oxidative power should be improved by the addition 

 of oxidizing substances, organic or inorganic, or, better, by treat- 

 ment which favors their formation, such as the addition of lime 

 and manure to acid soils, of manure and manganese to nonacid 

 soils. In soils of high oxidation power much further increase in 

 the oxidation power may indeed be harmful. Excess of manganese 

 in soils has been found injurious, as shown by the work of Loew 

 and Sawa 2 on rice, peas, and cabbage; of Salomon 3 on wheat; 

 by the investigations of Kelley 4 on Hawaiian soils; and of Guthrie 

 and Cohen 5 on the failure of grass on Australian soil. When man- 

 ganese is added its effect will undoubtedly vary with the nature of 

 the soil, the nature of the crop, the form of the manganese added, 

 and the nature of the associated organic matter. In general its effect 

 is to promote oxidation. In the presence of carbohydrates it may 

 cause reduction of nitrates, through the reducing compounds formed 

 in the oxidation of the carbohydrates. A review of the literature on 

 manganese as a fertilizer shows its effect has been variable. 6 



What quantities of manganese should be used in a soil to obtain 

 favorable action can be determined at present only by experimenta- 

 tion. In this paper it is pointed out that, on the acid soil of the 

 experiment farm, 50 pounds of manganese sulphate to the acre 

 decreased crop yields and gave in general a reduced rather than an 



J Corapt. rend., 138, 783 (1904). 



» Bui. Col. Agr. Tokyo, 5, 161 (1902-3). 



» La Staz. per. agr. Ital., 38, 1015 (1905); 40, 97 (1907). 



* Hawaiian Sta. Press Bui. 23; J. Ind. Eng. Chem., I, 533 (1909); Buls. 26, 28, Hawaii Agr. Sta. 



6 Agr. Gaz. New South Wales, 21, 219 (1910). 



« Bui. 73 and Circular 75, Bureau of Soils, U. S. Dept. Agr. 



