ACTION OP MANGANESE IN SOILS. 27 



plants from the manganese plot than from the check plot. The 

 relative oxidation, in fact, was 97 and 100, respectively. 



In neutral solution the oxidation power of the plant root is 

 increased by manganese sulphate, though manganese sulphate itself 

 has little oxidizing action on aloin, except in the presence of hydrogen 

 peroxide or activating organic matter. Addition of 0.5 c. c. of a 3 

 per cent hydrogen peroxide added to 70 c. c. of aloin solution shaken 

 with soil greatly increased the oxidation of the soil from the plots, 

 the manganese fertilized plot in particular. It is quite possible that 

 the soils which normally give direct oxidation of aloin contain both 

 organic and inorganic peroxide. It has been found, in fact, that 

 organic matter in a state of autoxidation forms peroxide. 1 Alkalies 

 and alkaline salts favor the formation of the peroxides. 



As analyzed by Mr. W. O. Robinson, of the Bureau of Soils, the 

 soil from the various parts of the experiment farm varied in manga- 

 nese content, calculated as MnO, from 0.034 per cent to 0.064 per 

 cent. The manganese-treated plot contained 0.060 per cent MnO, 

 the check plot 0.064 per cent. Of 26 American soils analyzed by 

 Robinson, 2 the average content of manganese was 0.071 instead of 

 0.20 per cent MnO previously given. The experiment farm has, 

 therefore, an average manganese content. 



Soils may have practically the same quantity of manganese and 

 still vary greatly in oxidizing power, so oxidation in soils, if due to 

 manganese, depends on the nature of the manganese as much as 

 on the amount. In previous work 3 it was found that soils of strong 

 oxidizing power, such as the Hagerstown loam and the Clarksville 

 silt loam, contain considerable manganese, while the Takoma loam 

 soil, the Elkton silt loam, and the Cecil sandy loam, which have 

 very little oxidizing power, contain little manganese. When 100 

 parts of manganese per million in the form of the sulphate, chloride, 

 carbonate, and dioxide were added to the three soils poor in manga- 

 nese, no increase in the power to oxidize aloin was noted in the case 

 of the chloride, sulphate, or carbonate, and the dioxide produced 

 but slight increase. When, however, dilute organic hydroxyacids, 

 such as citric, malic, and tartaric, 5 c. c. n/10 acids to 100 grams 

 of soil, and corresponding salts, such as sodium citrate and sodium 

 tartrate, were added to the soils to which the manganese had been 

 added, there was a decided increase in the power to oxidize aloin. 

 The greatest increase in oxidation occurred in the soils to which 

 manganese dioxide and citric acid had been added. Addition of 

 citric acid and sodium citrate to the soils from manganese-treated 



i Schonbein, J. prakt. Chem., 81, 16 (1860). Manchot and Herzog., Liebig's Ann. Chem., 316, 318, 331 

 (1901). Bach, Monit. Sci. (4), 11, II, 479 (1897) ; Compt. rend., 126, 1066, 4159 (1898). 



4 M. X. Sullivan and W. O. Robinson, Manganese as a fertilizer. Circ. 75, Bureau of Soils, U. S. Dept. 

 Agr. (1913). 



» Bui. 73, Bureau of Soils, U. S. Dept. Agr. 



