243 

 NEW SOIL STUDIES.* 



It is a curious fact that, while the relation of the plant to the 

 soil in which it grows is one of the most important among the 

 environmental relations of the organism, yet plant physiologists 

 and ecologists have so far paid almost no attention to the details 

 of the nature and behaviour of the soil solution. This is perhaps 

 due to the extreme difficulty of the problems involved, but they 

 are seemingly no more difficult than the problems of absorption, 

 photosynthesis, &c, with which botanists have successfully 

 grappled. The work so far accomplished has been done almost 

 entirely by students of agriculture who are not primarily interested 

 in the science of botany but in its applications. 



For some years the members of the laboratory staff of the 

 Bureau of Soils of the U. S. Department of Agriculture have been 

 following this line of enquiry in a truly research spirit, and have 

 brought out a number of valuable contributions. In Bulletin No. 

 41 of that Bureau, Frank K Cameron and James M. Bell present 

 the results of a study of " The Action of Water and Aqueous 

 Solutions upon Soil Phosphates." The discussion lies mostly in 

 the realm of physical chemistry, as must naturally be the case, 

 but direct application of the facts brought out is made to the 

 theory of fertilizer practice in agriculture. " The phosphates of 

 the soil are of such a nature as to yield a solution 



containing very small quantities of phosphoric acid. * 



The least soluble phosphates are the ones which will be formed 

 and will control the concentration of the soil moisture. This fact, 

 together with the well known phenomena of absorption, gives a 

 satisfactory explanation of the observation that the concentration 

 of the soil moisture is low and varies but little for different soils 

 and with the total amount of phosphoric acid in the soils. For 

 the same reason, the addition of phosphatic fertilizers can not be 

 expected to influence materially the concentration of phosphoric 

 acid in the soil moisture. The action of phosphatic fertilizers 

 is, therefore, on the soil and not primarily on the plant ; for the 

 concentration in plant food constituents of the solution on which 

 the plant feeds is not materially altered by the addition of 

 phosphatic fertilizers in the amounts used in ordinary field 

 practice." 



B.E.L. 



Few scientific theories have stood the test of time and experi 

 ment so long and gained such universal acceptance as the Liebig 

 theory of soil fertility. Nevertheless, recent investigations seem 

 to indicate that this conception is likely to undergo considerable 

 modification in the near future, suggesting that the " exhaustion" 

 of many soils may be due, not so much to the withdrawal of 

 mineral constituents as to the accumulation of certain organic 

 toxic substances. This idea is not a new one, for as long ago as 

 1832 DeCandolle stated that many plants give off in their growth 

 substances which are injurious to themselves and to closely 



* From " The Plant World," Vol. 10, No. 9, September, 1907, pp. 209-213. 



