
TY  - JOUR
A1  - Close, EA 
A1  - Powell, HKJ 
T1  - Rapidly extracted (0.02 <sub>M</sub> CaCl<sub>2</sub>-soluble) reactive aluminum as a measure of aluminum toxicity in soils
JF  - Soil Research
JO  - Soil Res.
Y1  - 1989
VL  - 27
IS  - 4
SP  - 663
EP  - 672
KW  - 
UR  - https://doi.org/10.1071/SR9890663 
N2  - This paper examines the use of short extraction times, and the determination of aluminium with chrome azurol S (CAS), for the estimation of 0.02 M CaCl2-soluble aluminium in soils. It reports the correlation between CAS-reactive aluminium in 5 min extracts and percent maximum yield of white clover (Trifolium repens) for a series of acid soils. The reactivity of soluble and colloidal aluminium species with the metallochromic reagent CAS has been assessed. ~ l ( a q ) ~ + , simple hydroxy species and complexes of weakly binding ligands (salicylic acid, tannins) are CAS-reactive (2 rnin). In contrast, complexes of strongly binding ligands (citric acid, fulvic acid) are not CAS-reactive ([Al] ~ [L] ~ [CAS] ~ 1-2~10-5 M). For a series of six limed phosphated topsoils and subsoils (pH 4.2-5.5), 0.02 M CaCl2- soluble aluminium, as determined with CAS, was negatively correlated against the percent maximum yield of white clover; r2 = -0.73** (5 min extraction), n = 20. This correlation is similar to that for yield against total aluminium as determined by atomic absorption spectroscopy after 60 min extraction (r2 = -0.77**). However, the colorimetric analysis is more convenient and sensitive; further, it does not measure colloidal and polymeric aluminium species (which may not be plant-available). The satisfactory correlation achieved for short extraction times suggests use of CAS for a rapid field method for aluminium toxicity in soils. 
ER  -

