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Solute Movement in the Rhizosphere$
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Peter B. Tinker and Peter Nye

Print publication date: 2000

Print ISBN-13: 9780195124927

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195124927.001.0001

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Soil and Plant Water

Soil and Plant Water

(p.14) 2 Soil and Plant Water
Solute Movement in the Rhizosphere

Peter B. Tinker

Peter Nye

Oxford University Press

Water is of central importance in the transport of solutes, whether by diffusion or mass flow, and whether in soils or plants (Lösch 1995). It is also extremely important for the biota that live in the soil (Parr et al. 1981). Water is an unusual component of the environment, because its structure suggests it should be a gas at normal temperatures rather than a liquid, and it is the only common compound in the biosphere that occurs to a significant extent in the vapour, liquid and solid phases. We begin this chapter with a very brief statement of the thermodynamic approach to the study of water, which defines the water potential. Without an understanding of chemical potentials, it is difficult to deal with the relationships of ions and water in the soil and the plant. Therefore, in this chapter we give an introduction to this subject with special reference to water, which we then take further in chapters 4 and 5. A clear exposition of this is given in Nobel (1991). The concept of chemical potential is fundamental. It is a measure of the energy state of a particular compound in a particular system, and hence of the ability of a unit amount of the compound to perform work and thereby cause change. In particular, the difference in potential at different points in a system gives a measure of the tendency of the component to move from the region with the high potential to the region with the low potential. A component of a system can have various forms of potential energy in this sense, all of which contribute to the total chemical potential. Here, we exclude chemical reaction energy and kinetic energy. The main forms of energy that contribute to the chemical potential of a specified compound or material are due to its concentration (which may release energy on dilution), to its compression (which may perform work on expansion), to its position in an electrical field (which may release energy if the component is electrically charged and moves within the field), and to its position in the gravitational field (which may release energy as the component moves downwards).

Keywords:   Agave, Broad bean, Casparian band, Dwarf bean, Hydraulic conductivity, Infiltration, Maize, Osmotic potential, Resistance equation, Salkum silty clay loam

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