ACTION OF MANGANESE IN SOILS. 19 



sive oxidation was noticeable ; the leaves were yellow at the tips and 

 appeared bleached. The natural processes of oxidation in the pro- 

 ductive soils were good, and the addition of manganese caused exces- 

 sive action, and thus injured the culture as a medium for growth. 

 The life processes in the unproductive soils were probably bad, and 

 the addition of this substance aided the needed function and therefore 

 overcame its bad qualities and made it a better medium for plant 

 growth. 



In relation to the beneficial effect of manganese on poor soils by 

 stimulating root oxidation where oxidation is naturally poor, and the 

 harmful effect by causing additional oxidation by plant roots in good 

 soils where the oxidation processes are already good, it is interesting 

 to note the effect of different fertilizers, which increase or check 

 oxidation on the action of organic compounds. Quinone, which has 

 been shown to be toxic to wheat seedlings in a former research, 1 is an 

 oxidizing substance. Its harmful effect is partly overcome by potash 

 salts, which check oxidation processes. On the other hand, those 

 harmful soil organic compounds that have reducing properties — that 

 is, are themselves readily oxidized — such as vanillin and dihydroxy- 

 stearic acid, have an inhibiting effect on root oxidation and on root 

 growth generally, and their harmful effects are overcome by fertilizers 

 such as nitrate, which increase root oxidation to the greatest extent. 



EXPERIMENTS WITH MANGANESE IN THE FIELD. 



The tests with manganese sulphate made at the department farm 

 at Arlington, Va., were laid out in the spring of 1907 and are a part of 

 a larger experiment, which includes the testing of a number of other 

 compounds and fertilizers. Five crops are concerned in each treat- 

 ment. The crops grown were wheat, rye, corn, cowpeas, and potatoes. 



Describing only the manganese plots in this series, it should be said 

 that these consisted of two parallel strips of land, each 1 rod wide 

 and separated by a 3-foot path. Each strip is divided into 5 plots 

 of 1 square rod, with 2^-foot paths separating the plots. One strip 

 or series of 5 plots is treated with manganese sulphate, the other strip 

 is not treated and serves as a control or check. The five different 

 crops are grown on both the treated and untreated plots, which lie 

 side by side in the two strips. 



The soil on which these experiments were made is a silty clay loam, 

 low in organic matter. The physical condition of the soil is rather 

 poor. Great care had to be practiced in cultivation to keep the soil 

 in a good physical condition. The ground on which the manganese 

 experiments were made is level and has surface drainage. The soil 

 throughout these manganese plots and their controls is uniform, so 



• Schreiner, O., and Skinner, J. J., Organic compounds and fertilizer action. Bui. 77, Bureau of Soils, 

 U. S. Dept. Agr. (1911). 



