Abstract
Numerous chemical species of aluminum (Al) occur in acid soils and simple but accurate methods are needed to characterize phytotoxicity. Kinetic reaction studies between Al and ferron were used to separate Al into instantaneously reactive (Ala), metastable (Alb), and non‐reactive (Alc) fractions in soil solutions of two North Carolina Ultisols. Relative root growth of field‐grown corn (Zea mays L.) was used to assess rhizotoxicity of kinetically measured Al forms. Reaction of Alb with ferron conformed to first order kinetics, with rate constant values ranging from 0.53 to 9.13 minute‐1. The Ala fraction correlated significantly with Al reacting in 30 seconds (r2=0.99), but the former averaged 10% less than the latter. Both Ala and Al reacting in 30 seconds correlated significantly with the Alb fraction (r2≥0.89), but not with the Alc fraction (r2<0.1). Correlation exercises between ferronreactive Al fractions and various Al species predicted by the GEOCHEM‐PC speciation program revealed a strong relationship between Ala and the sum of activities of Al3+, Al(OH)2+, and A1(OH)2 +, suggesting an instantaneous reaction of these species with ferron. The Ala and Ab fractions correlated significantly with root growth. The Alc fraction did not correlate significantly with root growth and may be relatively less toxic. Further soil solution studies may be required to ascertain the nature of actual Al species measured in the Ala and Ab fractions.