76 



ence of manganese in the soil solution, rather than to 

 organic toxic bodies. 



5. When dried blood is the source of nitrogen, solu- 

 ble manganese is believed to be due to the action of 

 nitric acid developed by nitrification. 



6. When ammonium sulphate is the source of nitro- 

 gen, nitrification is apparently unnecessary in order to 

 increase the amount of soluble manganese in acid soils. 



7. Reduced growth appears to be due chiefly to the 

 injury to plant roots, from the direct action of manga 

 nese, rather than to reduced or altered oxidation of 

 soil organic matter. 



8. A part of the injury may also be due to the effect 

 of manganese on the foliage. Plants with bleached 

 leaves are frequently found in both soil and water cul- 

 tures when soluble manganese is present. 



9. Relatively large amounts of manganese w^ere re- 

 covered from the soil obtained from the Pennsylvania 

 Experiment Station. Water extracts of this soil were 

 highly toxic to seedling plants. 



10. When the manganese was precipitated from 

 these extracts they supported a vigorous plant growth. 



11. Apparently, the relative amount of soluble man- 

 ganese is of more importance, within certain limits, 

 than is the total amount. The presence of considerable 

 amounts of calcium salts in an extract reduces the tox- 

 icity of manganese. 



12. Precipitataion of a part of the manganese b^^ 

 means of bases is much more effective in reducing tox- 

 icity than is dilution. Calcium, sodium, and potassium 

 hydroxides were found to be very effective when used 

 in this way, 



13. A large number of acid soils from Alabama 

 contained soluble manganese, after incubation with 

 dried blood or ammonium sulphate. Soluble manga- 

 nese has not been found in any of the basic soils, or in 

 any of the acid soils which had been thoroughly limed. 



14. The products of sulfofication appear to be very 

 effective in dissolving manganese in acid soils. 



1.5. It is believed that this work throws light on the 

 conflicting results obtained by different workers who 

 have used manganese as a fertilizer. Manganese salts 

 applied to basic so»ils would rapidly be changed, the 

 manganese going out of solution. When applied to 

 acid soils, the manganese salt would persist as such, 

 and heaw aplications would likely cause injury. 



16. Work on several phases of this usbjcct is being 

 continued. 



