PREVENTION OF ALUMINUM TOXICITY WITH SUPPLEMENTAL BORON .2. STIMULATION OF ROOT-GROWTH IN AN ACIDIC, HIGH-ALUMINUM SUBSOIL

Root growth inhibition is an early symptom of Al toxicity and B defici ency. Our hypothesis is that Al toxicity may induce B deficiency, and it was our objective to determine if incorporation of supplemental B w ould promote root penetration into an acidic, high-Al subsoil. Alfalfa (Medicago sativa L, cv, Hy-Phy) was grown in slanted tubes with a Ple xiglas window along their length. The top half of the tube contained s ilt loam soil and the bottom half contained subsoil from the Bt1 horiz on (26% Al saturation) of a Creldon silty clay loam. Both soils origin ally contained 0.9 kg B ha(-1), When root growth was measured in the b ottom half of the high-Al subsoil, all measurements - depth of rooting , total root growth, final root lengths and root dry weight - demonstr ated greater root growth in treatments where additional B was incorpor ated into the high-Al subsoil. Results from this soil study extend tho se obtained in our hydroponic study in which supplemental B prevented Al inhibition of root growth. Boron concentrations may need to be incr eased under acidic 'high-Al' soil conditions to promote root penetrati on into these soil zones, and this could be especially important durin g periods of drought stress.