ACTION OP MANGANESE IN SOILS. 31 



In wheat and rye plots, the catalytic power is greater in the manga- 

 nese-treated soils than in the untreated soil. In the corn and cowpea 

 plots the untreated soil is on the average slightly the better cata- 

 lyzer. In the case of potatoes, the check plot is slightly the better 

 catalyzer. The soil of the plots is not a strong catalyzer, and the 

 differences between the plots is slight, with the exception of the wheat 

 plots. 



Catalysis has been shown 1 to stand in closer relation to the man- 

 ganese content of the soil than oxidation, though even in the case 

 of catalysis the nature of the associated organic matter is of great 

 importance. Addition of manure leachings and of manure ash in- 

 creased the catalytic power of the soil of the experiment plots, but 

 their effect was not studied in connection with manganese. 



In general, soils of high productiveness previously studied have 

 had strong catalytic power, while poor soils have had, as a rule, weak 

 catalytic power. The catalytic power, however, does not stand in 

 as close relationship to soil fertility as the oxidation power does, 

 though in general the presence of a strong catalytic power in a soil can 

 be taken as a priori evidence that the many factors making for soil 

 fertility, such as suitable organic matter, bacterial activity, oxidation, 

 etc., would be prominent and the soil would be a productive soil. 

 Factors which favor fertility and oxidation, such as liming and addi- 

 tion of manure, also favor catalysis. Though crop production is 

 dependent on many factors, no one or two of which can be taken 

 as an absolute criterion, it is interesting to note that the soil of 

 the experiment plots is a poor oxidizer and catalyzer and is also of 

 mediocre productiveness. Its poor oxidation and catalysis and like- 

 wise yields of the ordinary cultivated crops may be connected with 

 the acid character of the soil. In a similar way the lack of favorable 

 response in oxidation, in catalysis, or in crop growth to treatment 

 with manganese may be connected with the acid reaction and small 

 organic content or the nature of the latter. 



SUMMARY. 



The effect of manganese on poor and good soils was studied by 

 growing wheat in pots. Manganese chloride, sulphate, nitrate, car- 

 bonate, and dioxide had a stimulating effect in the case of an unpro- 

 ductive sandy loam soil. The best results were obtained when the 

 salt was applied in amounts from 5 to 50 parts of manganese per mil- 

 lion. Quantities higher than this gave no correspondingly larger 

 increase and in some cases were even harmful. On a productive loam 

 the various salts of manganese had no stimulating effect. 



Further work was done by growing the crop in treated aqueous 

 extracts of soils and studying the oxidizing power of the plants. The 



i Bui. 86, Bureau of Soils, U. S. Dept. Agr. 



