Postprint version. Published in Communications in Soil Science and Plant Analysis, Volume 19, Issue 7-12, May 1, 1988, pages 857-871.
Copyright © 1988 Taylor & Francis. This is an electronic version of an article published in Communications in Soil Science and Plant Analysis.
NOTE: At the time of publication, the author G.S.P. Ritchie was not yet affiliated with Cal Poly.
The definitive version is available at http://dx.doi.org/10.1080/00103628809367980.
Three equations for estimating the concentration of free aluminium, [Al3+], from the activity of free fluoride, (F-), were compared to assess their suitability for estimating [Al3+] in acid soil solutions and in competition studies. We then studied the ability of humic acids to compete with F for Al by comparing the behaviour of the humic acids in the presence of F and Al with that of several carboxylic acids under the same conditions. All three methods of estimating [Al ] were limited in their applicability to acid soil solutions but were uitable for estimating [Al3+] in competition studies when equimolar quantities of AlT and FT were used. Humic acids extracted by NaOH and by Na2H2P2O7 decreased the amount of Al complexed with F by 21 -100% at pH 4 and 6 and ratios of Cmoles of humic acid: F>l. The Al humate complex precipitated when the Al: humic acid ratio was >1. Both humic acids appeared to be more effective than simple carboxylic acids at competing with F for Al.
Food Science | Nutrition