ABSTRACTIn contrast to experience with normal soils, reducing the pH (alkalinity) of alkali soils by using gypsum has been reported to result in lowering the amounts of DTPA-Zn. We studied the nature of pH dependence of Zu activity in alkali soil distinguishing between adsorption-exchange and precipitation reactions. The surface horizon sample of an alkali soil was Zn-saturated at pH 5.0. The Zn-soil was leached sequentially with 0.5 M NaCl and Mg(NO3)2 solutions adjusted between pH 5–9.5 and 0.1 M HCl. Results indicated that an increase in soil pH increased the negative charge of soil particles and also increased the exchangeability of sorbed Zn. At the high pH commonly observed in alkali soils, precipitation reactions controlled Zn solubility. Reclamation of alkali soils changes the proportions of precipitated and specifically sorbed Zn importantly. Lowering the pH of alkali soils will dissolve zinc precipitates and increase the specifically sorbed Zn, well known for its low desorbability. It appears that crop production on alkali soils will need small fertilizer Zn doses on a continuous basis for greater fertility efficiency.
In contrast to experience with normal soils, reducing the pH (alkalinity) of alkali soils by using gypsum has been reported to result in lowering the amounts of DTPA-Zn. We studied the nature of pH dependence of Zu activity in alkali soil distinguishing between adsorption-exchange and precipitation reactions. The surface horizon sample of an alkali soil was Zn-saturated at pH 5.0. The Zn-soil was leached sequentially with 0.5 M NaCl and Mg(NO3)2 solutions adjusted between pH 5–9.5 and 0.1 M HCl. Results indicated that an increase in soil pH increased the negative charge of soil particles and also increased the exchangeability of sorbed Zn. At the high pH commonly observed in alkali soils, precipitation reactions controlled Zn solubility. Reclamation of alkali soils changes the proportions of precipitated and specifically sorbed Zn importantly. Lowering the pH of alkali soils will dissolve zinc precipitates and increase the specifically sorbed Zn, well known for its low desorbability. It appears that crop production on alkali soils will need small fertilizer Zn doses on a continuous basis for greater fertility efficiency.
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