ORGANIC CONSTITUENTS OF THE SOIL SOLUTION 83 



to plant growth. These experiments were then repeated in 

 a modified form by shaking the poor solution with such ab- 

 sorbents as precipitated ferric oxide or carbon black and filtering 

 before adding the seedling plants. The solutions thus pre- 

 pared proved very satisfactory nutrient media, although the de- 

 cided elongation of the roots, always observed when the ab- 

 sorbents were in contact with the solutions, was not so notice- 

 able with these filtered solutions. 



.The experiments just described were repeated with extracts 

 from a number of soils which were supporting or had recently 

 supported poor crops. The accumulated mass of evidence ad- 

 mits of no doubt that in many cases the apparent lack of fertility 

 of a soil is due to the presence of some organic substance or 

 substances soluble in soil water. This point established, there 

 was studied the effect of fertilizers when added to aqueous ex- 

 tracts from poor soils. 



A large amount of experimenting has been done on this sub- 

 ject. It has been found that the common commercial fertilizers, 

 as well as many other substances, when added to the soil ex- 

 tract containing growing plants, sometimes improve the plants, 

 sometimes the contrary. But, in general, those particular sub- 

 stances which improve any given soil for a crop also improve the 

 aqueous extract of the soil for the growth of the same crop plant ; 

 *. e., should a soil be known to respond well to the application of 

 superphosphates when planted to wheat, then the probability is 

 great that the aqueous extract of the soil will be improved as a 

 culture medium for the wheat plant by addition of calcium 

 phosphate. Particularly important in this connection are cer- 

 tain experiments with organic fertilizers. 



A soil which had been found to be quite unproductive with 

 regard to wheat and ordinary tame grasses yielded, however, 

 a much better growth of plants if pyrogallol or better pyrogallol 

 and lime were added to the soil some days before planting. An 

 aqueous extract of this soil tested with young wheat seedlings 

 produced but a poor growth, as did the soil itself. But with 

 the addition of pyrogallol or pyrogallol and lime to the soil ex- 



