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 
i Compt. 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, 
