31 6 Journal of Agricultural Research voi. xii. no. 6 



Ballenegger (2) has used the methods of the Bureau of Soils, as well 

 as determinations of electrical conductivity, in the study of 75 typical 

 Hungarian soils. He concluded that the character of the water solu- 

 tions may be used to differentiate the various types of soil. The soils 

 investigated varied from the poor gray forest soils to the very fertile 

 ''at fold" soils. 



Toulaikov {56, 37) believed, like Gola (19), that the osmotic pressure 

 of the soil solution was the important factor in plant growth. He 

 found the optimum to be a pressure of three atmospheres and that the 

 growth of wheat was benefited by an increase up to that point. 



Pantanelli {44) has attempted to study the concentrations of the 

 solutions of soils from Tripoli by determining the electrical conductivity 

 of the liquids obtained by percolation. He was able by this procedure 

 to differentiate between several classes of cultivated and virgin soils. 



Hall, Brenchley, and Underwood (25) have reported a noteworthy 

 investigation in which the soils from the Rothamstead experiment plots 

 were used. Solutions were prepared using 20 kgm. of soil and 35 kgm. 

 of water, and wheat and barley plants were grown therein. From the 

 analysis of these solutions and the growth of the plants in them it was 

 concluded that — 



The composition of the natural soil solution as regards phosphoric acid and potash 

 is not constant, but varies significantly in accord with the composition of the soil 

 and its past manurial history. Within wide limits the rate of growth of a plant varies 

 with the concentration of the nutritive solution irrespective of the total amoimt of 

 plant food available. When other conditions such as the supply of nitrogen, water 

 and air are equal, the growth of crops will be determined by the concentration of the 

 soil solution in phosphoric acid and potash; which, in its turn, is determined by the 

 amount of these substances in the soil, their state of combination and the fertilizer 

 applied. 



These authors' did not find any toxic effect on soils which had grown 

 wheat and barley for even 60 years. Growth in the soil solutions agreed 

 with the growth in culture solutions containing equivalent amounts of 

 phosphoric acid and potash. 



In a series of nutritive solutions of various degrees of dilution the 

 growth varied directly, but not proportionately, with the concentration 

 of the solution. 



Finally, the authors concluded that the results of the investigation 

 restored the earlier theory of the direct nutrition of plants by means of 

 fertilizers and nullified the theories advanced by Whitney and Cameron 



(.61). 



Bouyoucos and McCool (5) have proposed an ingenious method for 

 determining the concentration of the soil solution directly by means of 

 the freezing point. Use has been made of this procedure in the present 

 investigation by Hoagland, and its application and limitation are dis- 

 cussed in a separate paper (27). 



