Determination of toxic aluminum for wheat roots by potentiometry with fluorid ion selective electrode

Abstract

A potentiometric technique with fluoride ion selective electrode (FISE) was evaluated for its ability to estimate toxic Al species for wheat root growth in pure and soil solution, and in limed and unlimed treatments of selected acid soils. Al-FISE was compared with a spectrophotometric-ferron method. Root growth decreased exponentially with increasing Al-FISE. The dominant forms of Al-ESIF was estimated by Geochem as A1³⁺, AlOH²⁺, and Al(OH)²⁺. Al--FISE concentration in unlimed soil solution ranged from 30 to 2100 x 10^-6M and decreased with increasing soil pH. Al-ferron was greater than Al-FISE for all pH studied. Above pH 5.6 Al-FISE was undetectable but Al-ferron increased in soils high in dissolved organic carbon. Al complexes above pH 5.6 was reactive with ferron but not with F^- ion. Al-FISE was better predictor of the toxic Al species for wheat root growth than Al-ferron.