THE SOIL SOLUTION 287 



remarkable infltience on the soil solution, especially increasing 

 its concentration during the warmer seasons. Plowing and 

 cultivation by stimulating biological activity may enhance ni- 

 trate production to a marked degree in a short time. Aeration 

 will often increase the available mineral elements by the en- 

 couragement of reactions which favor solution. The addition 

 of salts of various kinds has been shown by Bouyoucos^ to 

 influence the soil solution profoundly. The compounds added 

 affected different soils in a diverse manner. When neutral 

 salts were added, the soil solution was increased from 35 to 

 100 per cent, of the added strength of the salts. In the case 

 of phosphate salts the increase was very much less. 



150. The soil solution and productivity. — ^As the crop 

 obtains its nutrients from the soil solution, there must be a 

 direct relationship between the fertility of the soil and the con- 

 centration and composition of the soil solution. The data 

 quoted from Hoagland indicate in a broad way that a fertile 

 soil is capable of maintaining a more concentrated soil solu- 

 tion than is a poorer one. The work of other investigators 

 amply corroborates this assumption.^ One rather convincing 

 experiment may be quoted. 



Hall, Brenchley, and Underwood^ analyzed the water ex- 

 tract from certain plats on the Eothamsted Experiment Sta- 

 tion farm, the fertilizer treatment and the yields of which 

 had been recorded for a long term of years. Complete analyses 

 of the soil from the several plats were also made : 



^ Bouyoucos, Gr. J., The Freesing Point Method as a Means of Studying 

 Velocity Reactions Between Soils and Chemical Agents and Behavior of 

 BquiWbrium ; Mich. Agr. Exp. Sta., Tech. Bui. 37, 1917. 



Also, Mate and JExtent of Solubility of Soils under Different Treat- 

 ments and Conditions; Micli. Agr. Exp. Sta., Tech. Bui. 44, 1919. 



See also, Spurwaj, C. H., The Effect of Fertiliser Salt Treatments on 

 the Composition of Soil Extracts; Micli. Agr. Exp. Sta., Tech. Bui. 45, 

 1919. 



*See citations page 284. 



«Hall, A. D., Brenchley, W. B., and Underwood, T. M., The Soil 

 Solution and the Mineral Constituents of the Soil; Phil. Trans. Boy. 

 Soc, London, Series B, Vol. 204, pp. 179-200, 1913. 



