26 



BULLETIN 42, U. S. DEPARTMENT OF AGRICULTURE. 



Table XVII. — Relative oxidation in plots treated with manganese sulphate and in the 

 corresponding check plots growing the same crop {wheat soil in April taken as 100). 





Crop. 



April. 



June. 



August. 





Check 

 plots. 



Manganese 

 plots. 



Check 

 plots. 



Manganese 

 plots. 



Check 

 plots. 



Manganese 

 plots. 



Wheat 



100 



131 



110 



66 



87 



95 

 105 

 100 



64 



60 



110 

 131 

 130 

 105 

 91 



130 

 105 

 131 

 110 



78 



55 



78 

 87 

 53 

 53 



64 



Rve 



60 





75 



Cowpeas 



53 







55 









With the exception of the wheat plot, where there is shown a 

 slight increase as an average of the three determinations, the addi- 

 tion of manganese sulphate has not increased the oxidative power 

 of the soil, and in a number of instances it has lessened oxidation. 

 The soil in general has a tendency to be acid in character and at best 

 has not a strong oxidizing power. If the first determination, made 

 in April, is considered (that is, the oxidative power of the plots at a 

 time when there is little or no growth) the oxidation in the manganese 

 plot is less in every instance than that of the check plot. This period 

 is the best one for testing the oxidation effect of manganese unmodi- 

 fied by plant growth. The lessened oxidation produced by manga- 

 nese sulphate agrees roughly with the lessened yields on the same 

 plots under treatment with manganese. In 1912, for instance, the 

 year in which the oxidation was tested, the yield, as previously 

 shown, of wheat, corn, and potatoes was less on the manganese plot 

 than on the untreated plot, while rye showed a slight increase and 

 the yield of cowpeas was practically the same. 



In the second determination, made in June, the oxidation power 

 of the manganese plot is on the average more like that of the check 

 plot. 



In the third determination, made in August, shortly after wheat 

 and rye had been taken off, the manganese plot was on the average 

 again less than the check plot. 



As previously pointed out, the manganese plots, with the exception 

 of the potato plot, showed a higher lime requirement than the check 

 plots. Under acid conditions the formation of organic compounds 

 capable of acting as oxygen carriers or as activators of inorganic 

 oxidizing compounds such as manganese salts is much lessened 

 or entirely inhibited. This is indicated from the results with the acid 

 soil under investigation, for the addition of manganese did not in- 

 crease the oxidizing power of the soil nor indeed of plants growing 

 therein. This oxidizing power of the plants was tested in the case of 

 wheat. By carefully removing the soil from the young wheat plants 

 growing on the plots, the oxidizing power of the intact roots when 

 placed in aloin solution was found to be no greater in the case of the 



