Authored by: Sven Schubert

Handbook of Plant Nutrition

Print publication date:  May  2015
Online publication date:  May  2015

Print ISBN: 9781439881972
eBook ISBN: 9781439881989
Adobe ISBN:


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Sodium (Na), like potassium (K), is an alkali metal belonging to the first group in the periodic table of the chemical elements. Both of the elements are abundant in the earth’s crust, which is 2.6% Na and 2.4% K. They occur in various salts, and after dissolution of the salts form monovalent cations. Despite these striking similarities, K and Na differ considerably in their significance for the biosphere. Whereas K is considered a plant nutrient (see Chapter 4), Na, depending on the plant species, may act as a beneficial or toxic element (Kronzucker et al., 2013). The difference between the two monovalent cations is based on the ionic diameter, which in turn determines the surface charge. Because the ionic diameter of the nonhydrated Na+ is smaller (0.20 nm) than that of the nonhydrated K+ (0.27 nm), the surface charge of Na+ is higher, resulting in a larger diameter of the hydration shell. This size difference is the reason why K+ in most cases cannot be substituted by Na+ in the three major physiological functions, namely,

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