268 Vniversity of California Publications in Agricultural Sciences [Vol. 1 



HUMIC PHOSPHORIC ACID IN SOILS 



While one of the chief values of humus lies in its content of 

 nitrogen which is made available to plants by bacterial action, 

 the mineral elements potash and phosphoric acid held by it are 

 also of value to plants as fertilizers and are probably immedi- 

 ately available. The amount of phosphoric acid is especially 

 quite large, as is shown by an analysis of the ash from humus 

 of a productive prairie soil of IMinnesota made by Professor 

 Snyder. ^^ 



Table 49. — Analysis of the Ash of Humus 



Per cent 



Ash (precijiitated humus) 12.24 



Composition of the Ash 



Silica 61.97 



Potash 7.20 



Soda 8.13 



Lime 0.09 



Magnesia 0.36 



Ferric oxid 3.12 



Alumina 3.48 



Phosphoric acid 12.37 



Sulfuric acid 0.98 



Carbonic acid 1.64 



Early in the investigation of the humus in these soil columns, 

 we made examinations of the ash of the humus of a few of the 

 soil columns to their full depth to ascertain how much, if any, 

 phosphoric acid was present in an organic form combined with 

 the humus below the upper few feet. The difficulty of securing 

 a humus solution free from suspended clay makes the results 

 given in the following table only approximately correct, though 

 sufficiently so to be of special interest in showing that phosphoric 

 acid does accompany the humus in all soils to depths of many 

 feet, and being thus distributed downward throughout the soil 

 mass is at the command of roots as they reach to water. 



11 Chemistry of Soils and Fertilizers. 



