32 BULLETIN 42, U. S. DEPARTMENT OF AGRICULTURE. 
oxidation was tested after the plants had been growing for two weeks. 
The effect of manganese on the oxidizing power of the plant roots and 
on growth gave different results with different soils. 
With poor, unproductive soils manganese salts increased oxidation 
and growth. This was especially true in extremely poor soils and in 
a soil in which were found several harmful organic compounds. 
Some harmful soil constituents themselves check the oxidizing 
power of plant roots, and their harmfulness is overcome by fertilizers 
which stimulate oxidation. 
Oxidation was increased in productive soils; the growth, however, 
was decreased. The plants showed indications of excessive oxida- 
tion. As the oxidation processes in these soils were already good, 
the harmful action is attributed to excessive oxidation. 
The beneficial action of manganese may be due to its function of 
aiding and increasing the oxidation processes and other vital proc- 
esses in the plant as well as in the soil, and by this means changing 
or destroying some noxious products detrimental to plant growth. 
A 5-year field test with manganese sulphate was made, growing 
wheat, rye, corn, cowpeas, and potatoes. The experiments were 
made on a silty clay loam soil which is acid in nature. 
The manganese sulphate used at the rate of 50 pounds per acre had 
a harmful effect on each of the crops grown. 
The addition of manganese sulphate to the soil decreased rather 
than increased the oxidizing power of the soil, which at best does not 
possess strong oxidizing power. 
This is in harmony with the crop yield, which was also lessened 
by the addition of manganese sulphate, for while crop production is 
not absolutely correlated with the oxidative power of a soil, yet, in 
general, soils of good productivity are good oxidizers, and the factors 
which favor oxidation favor soil productivity. 
The catalytic power of the plots was slightly if at all increased by 
the addition of manganese sulphate. 
The soil is acid in character, which condition is unfavorable to 
oxidation and catalysis. 
The failure of manganese to increase these factors may therefore 
be due to the acid character of the soil. 
From these tests it is concluded that manganese is not profitable as 
a soil treatment on soil of this nature in need of liming. 
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