16 BULLETIN 42, U. S. DEPARTMENT OF AGRICULTURE. 



was able to alleviate the toxicity of such solutions. 1 The oxidizing 

 power of plants grown in extracts of productive soils is greater than 

 that of plants grown in extracts of unproductive soils. Harmful 

 organic compounds upon proper conditions suffer change in the soil. 

 This change may occur under conditions of thorough aeration and 

 oxidation, which is promoted by thorough tillage and good drainage 

 and also by the addition of substances to increase oxidation in the soil. 

 This seems to be a function of manganese. Its addition to extracts 

 of soils of low fertility increases the oxidation, and by so doing may 

 change the organic material of the solution and make it a better 

 medium for plant growth. 



EFFECT OF MANGANESE IN EXTRACTS OF PRODUCTIVE SOILS. 



The next experiments are concerned with the action of manganese 

 in good soils where harmful conditions are necessarily at their mini- 

 mum or entirely wanting. One of the soils tested was the Hagers- 

 town loam from a productive plot in the experimental field of the 

 Pennsylvania experiment station. The soil is naturally productive 

 and in the field has been subjected to a four-year rotation. When 

 tested in pots, this soil did not respond to manganese. 



An extract of the soil was made in the usual way and wheat seed- 

 lings grown. Manganese chloride, sulphate, and nitrate were used 

 in concentrations of 10 and 25 parts per million. Two cultures were 

 used in each treatment. The experiment was run from December 9 

 to December 23. The results are given in Table VII. 



Table VII. — Effect of manganese on growth and oxidation in extracts of a productive 

 loam soil. ( Untreated extract = 100.) 



Treatment. 



Relative 



Relative 



growth. 



oxidation. 



100 



100 



98 



98 



90 



97 



80 



100 



90 



102 



95 



101 



100 



100 



Extract untreated 



Extract+MnCl2, 10 parts per million 



Extract+MnCl2, 25 parts per million 



Extract+MnSOi, 10 parts per million 



Extract+MnSOj. 25 parts per million 



Extract+Mn(N0 3 )2, 10 parts per million. 

 Extract+Mn(NO a )2, 25 parts per million. 



As seen in the table, there was no increased oxidizing power of 

 the plant roots in the manganese cultures. The oxidation in the 

 untreated solution was very good, as might have been expected in 

 this highly fertile soil, and the addition of manganese produced no 

 additional oxidation by the plants. The growth was not increased. 

 In several instances it was decreased. Only in one treatment, and 

 that with the nitrate, was the growth as good as in the untreated 

 solution. 



1 Schreiner, O., and Reed, H. 8., The rdle of oxidation in soil fertility. Bui. 56, Bureau of Soils, U. S. 

 Dept. Agr. (1909). 



