Studies on plant growth‐regulating substances XLVIII. The effects of3,5‐diiodo‐4‐hydroxybenzoic acid on seedling growth in compact and loose soils

Abstract

SUMMARYInvestigations were carried out under growth room conditions to assess the effect on seedling growth of incorporating3,5‐diiodo‐4‐hydroxybenzoic acid (DIHB) in a silt loam soil.In ‘compact soil’ (bulk density 1–5 g/cm3) at 20% moisture content, DIHB significantly increased elongation of the roots of Hordeum and Pisum seedlings, the optimum concentrations being 0–005 [ig and 0–005‐0‐507 fig DIHB/g dry soil respectively. Shoot height and root and shoot dry weights were also improved in barley seedlings. Treated pea seedlings had smaller root diameters 1 mm and 5 mm behind the apices and the roots were less bent than those of seedlings grown in soil in the absence of DIHB. The efficacy of DIHB treatment on pea seedling growth in compact soil decreased in soils at 24 and 28 % moisture contents.In ‘loose soil’ (bulk density i‐i g/cm3) at 20% moisture content, DIHB significantly promoted the growth of barley seedlings but the only effects on pea seedlings were small changes in root diameter.