2 MANGANESE AS A FERTILIZER. 



been done in this bureau on the fertilizing value of manganese salts. 

 The detailed results of this work will be published in the near 

 future. 



Experiments on the after effects of manganese as a fertilizer are 

 too few to warrant any definite conclusion. Some Japanese work, 

 however, indicates that the ultimate after effect is not favorable. 



The stimulating effect of manganese on plant growth is due most 

 probably to its oxidizing activity and its influence on the oxidizing 

 power of plants, microorganisms, and soil. In connection with 

 plants manganese has been shown, through work in this bureau, to 

 be the most active element in promoting oxidation changes brought 

 about by the oxidizing enzymes. It has been found, too, that in 

 general the power of soils to oxidize easily oxidizable substances, a 

 power which is greater in fertile soils than in infertile soils, and in 

 surface soils than in subsoils, is correlated with the manganese con- 

 tent and the nature of the organic matter. In this connection it 

 is interesting to note that in a chemical examination of a number 

 of soils and subsoils the manganese was found concentrated in the 

 surface soil. In addition to furthering the necessary oxidation 

 changes in plant and soil, it has been found by a number of investi- 

 gators that manganese stimulates the growth of microorganisms, 

 modifying their number and functions with a consequent modifica- 

 tion of biochemical activities. As a result there is a change in both 

 the quantity and the condition of various soil constituents. Further, 

 it has been found that manganese added to the soil increases the ab- 

 sorption of other ingredients by the plant, particularly lime and 

 magnesia. 



Manganese is widely distributed in the soil. Of 26 American soils 

 that have recently been carefully analyzed by one of the authors, all 

 contain manganese (MnO) in proportions ranging from 0.01 to 0.51 

 per cent. The average content in these soils is 0.20 per cent, or 

 about 8,000 pounds in the acre-foot. This amount compares favor- 

 ably with that of phosphoric acid, though the quantity of phosphoric 

 acid assimilated by the plant is very much greater. 



In several soils, in Hawaii and in New South Wales in Australia 

 the natural manganese content is so high that it has been found 

 injurious to pineapples and grass, respectively. 



Manganese is present in the soil in at least two forms; one the 

 undecomposed silicate compounds, and the other manganese dioxide 

 (MnO,). 



Of the various compounds of manganese, the dioxide seems to be 

 the least effective, perhaps because the manganese is already present 

 in the soil in this form. The sulphate has received the most atten- 

 tion and has given the best results. Less work has been done with 

 the chloride, but in common with the sulphate, in small amounts, it 



