Prevention of aluminium toxicity with supplemental boron. II. Stimulation of root growth in an acidic, high‐aluminium subsoil
Root growth inhibition is an early symptom of Al toxicity and B deficiency. Our hypothesis is that Al toxicity may induce B deficiency, and it was our objective to determine if incorporation of supplemental B would promote root penetration into an acidic, high-Al subsoil. Alfalfa (Medicago sativa L. cv. Hy-Phy) was grown in slanted tubes with a Plexiglas window along their length. The top half of the tube contained silt loam soil and the bottom half contained subsoil from the Bt1 horizon (26% Al saturation) of a Creldon silty clay loam. Both soils originally contained 0.9 kg B ha -1 . When root growth was measured in the bottom half of the high-Al subsoil, all measurements - depth of rooting, total root growth, final root lengths and root dry weight - demonstrated greater root growth in treatments where additional B was incorporated into the high-Al subsoil. Results from this soil study extend those obtained in our hydroponic study in which supplemental B prevented Al inhibition of root growth. Boron concentrations may need to be increased under acidic 'high-Al' soil conditions to promote root penetration into these soil zones, and this could be especially important during periods of drought stress.