Effect of hydrogen on soybean root growth in a subsurface solution

Abstract

A vertical split-root technique was used to evaluate the effects of pH levels in a subsurface solution compartment on root development of soybean (Glycine max (L.) Merr.). The surface root compartment (12 cm) was filled with limed and fertilized soil. Treatments in the solution compartment were seven pH levels (3.7, 4.0, 4.3, 4.6, 4.9, 5.2, and 5.5) with 2 µM Ca, 18 µM B, and 0.5 µM Zn. Even when root growth in the subsurface solution compartment was restricted by pH, there were no differences in aboveground dry matter production. The number of other roots extending from the soil into the solution compartment increased with time and, at day 12, decreased by 13.3 roots/pot with each unit increase in solution pH. Final main root length increased 26.6 cm/plant with each unit increase in solution pH, while lateral root length increased exponentially. Low pH (< 4.3) inhibited lateral roots formation on main roots, and increased the number of other roots. At higher pH values the average length of laterals and number of other roots increased. At pH 3.7 other roots accounted for 88.3% of the total root length (TRL), main roots accounted for 11.7%, and lateral roots were not present. At pH 5.5 TRL was comprised by 15.1 % from other roots, 54.9% from main roots, and 30.0% from lateral roots. Low pH reduced the length of laterals more than main roots.