ACTION OF MANGANESE IN SOILS. 25 



After the crops were harvested in 1912, lime was added in sufficient 

 amounts to satisfy the lime requirements for the separate plots as 

 shown in Table XVI. Lime requirement tests will be made for each 

 plot after the crop is harvested each year, and should any further 

 lime be required this will be added, so as to maintain the soil, as 

 nearly as practicable, in a neutral condition. As manganese had 

 harmful effects on the soil when acid, it will be interesting to observe 

 its effect when the soil is kept neutral. 



OXIDATIVE POWER OF PLOTS WITH AND WITHOUT MANGANESE. 



Since Bertrand * showed that manganese played an essential part 

 in the oxidation by the so-called oxidizing enzyme, laccase, since 

 manganese increased the oxidizing power of a number of soils in the 

 laboratory, and since it has been found that a number of soils of 

 strong oxidizing power contain considerable manganese, some of 

 which was in the highly oxidizing form of Mn0 2 , it became of interest 

 to determine whether manganese had any accelerating effect on the 

 oxidation in the soil of plots planted with wheat, rye, corn, cowpeas, 

 and potatoes. 



In 1912 composite samples from five borings to the depth of 6 

 inches were taken of the manganese plots and check plots : (a) early 

 in April before the yearly application of fertilizer, when wheat and 

 rye were 4 or 5 inches high and before the corn, cowpeas, and potatoes 

 had been planted; (6) late in May, after the fertilizers had been 

 added, when the corn and cowpeas had sprouted; (c) in August, 

 after wheat and rye had been taken off, corn was in tassel, cowpeas 

 in bloom, and potatoes were coming into bloom. The oxidation 

 readings were made a week or two later on the air-dried samples. 



When 10 or 20 grams of soil are shaken two or three times with 

 50-70 c. c. of a 0.125 per cent water solution of aloin, the aloin solu- 

 tion is changed in a few minutes from bright yellow to a cherry red. 

 After the soil has stood for about an hour and has settled, the some- 

 what turbid solution is decanted and centrifuged, the supernatant 

 liquid drawn off, and the depth of color of the different solutions 

 compared by means of a Schreiner colorimeter, either with each other 

 or with colored glass of a shade of red matching one of the oxidized 

 solutions. In the present experiment the oxidation reading was made 

 against a glass standard, which matched in tint the red color produced 

 in the aloin solution by the sample of wheat soil collected in the 

 spring. Ten grams of soil were employed for each test. The rela- 

 tive oxidation in the manganese plots and the check plots is given 

 in the table following. 



i Compt. rend., 122, 1132 (1896); 124, 1032 (1897;. 



