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TRANSPORT PROCESSES IN 

 THE SOIL-PLANT SYSTEM 



Morell B, Russell and Joseph T. Woolley 



UNIVERSITY OF ILLINOIS 



Growth is a dynamic process in which energy and a variety of ma- 

 terials are transported within the organism and between it and the 

 environment. The transport conforms to certain basic physical laws 

 and, in principle at least, is susceptible to quantitative definition and 

 measurement. It is the purpose of this paper to examine the General 

 Transport Law in both its simple and its more complex forms and to 

 discuss its application to several of the flow phenomena that occur in 

 the soil-plant system. 



The analytic description of flow involves three major parameters. 

 These are the jlux, which expresses the quantity of the substance being 

 transported through a unit area in unit time; the driving force, repre- 

 sented by the gradient {i.e., space rate of change) of an appropriate 

 potential; and the transmission coefficient, which is the ratio of the flux 

 to the driving force and reflects the properties of the quantity flowing 

 and of the medium through which the flow occurs. Transport phenom- 

 ena may be formally described by the following General Transport 

 Law: 



where F is the flux, k is the transmission coefficient, and V ^ is the 

 gradient of the potential. 



Under the broad coverage of the General Transport Law, several 

 subgroups of flow phenomena may be identified. The non-turbulent 

 steady-state flow of an incompressible fluid through a completely filled 

 geometrically simple tube can be accurately described in terms of the 

 velocity of flow, the dimensions of the tube, the distribution of pres- 



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