Al toxicity in plants is related to the activity of Al3+ and Al-hydroxy monomers in the soil solution, whereas Al complexed with ligands such as fluoride (F), sulphate (SO42-), and oxalate is not toxic. Estimation of toxic Al relies on measurement of “labile”; Al after short contact times with colorimetric reagents or cation-exchange resins. However, shifts in equilibrium may result in non-toxic forms of Al reacting with the complexing agent or resin.

A series of laboratory experiments tested the degree to which labile Al is related to Al3+ in simplified media and compared methods of estimating labile Al in the presence of organic ligands and in soils. Cation-exchange resins extracted more than the theoretical concentration of Al3+ from solutions containing a range of concentrations of OH- and SO42-. More Al was extracted in 15 s by 8-hydroxy-quinoline than by Chelex-100 from solutions of Al-humate at pH 4. In sands which had been spiked with Al and organic matter, the estimation of labile Al varied with both the method of measurement and type of extract. The cations present in commonly used soil-extracting chloride solutions can decrease the proportion of organically complexed Al.


Food Science | Nutrition

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This is an electronic version of an article published in Communications in Soil Science and Plant Analysis.



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