| A vertical split root technique was used to evaluate effects of H{dollar}sp+,{dollar} Al, Ca, Mg and (Cl{dollar}sp-{dollar} and SO{dollar}sb4sp=){dollar} on root development of soybean (Glycine max (L.) Merr.) var. Ransom. Soybean shoot growth and root length in a compartment filled with topsoil were not affected by treatments imposed to the subsurface solution. At low pH, low Ca, high Al concentrations and at absence of B and Zn there was reduced length of all root components, increased lateral root density, and reduced distance from the main root apex to the youngest lateral root. Reduced root growth in solution was associated with low pH, low Ca, high Al, absence of B and Zn, otherwise they stimulated root branching in the soil compartment, and this led to a greater number of roots crossing the membrane with time. Lateral roots had greater sensitivity than main roots to low pH, low Ca and high Al. In the absence of Al, the Ca/H molar activity ratio was the best predictor of main root growth. There was no response in main root growth to increased Ca supply when Ca/H ratio was {dollar}>{dollar}1000. Aluminum toxicity to roots was modified by pH, Ca, Mg and accompanying anions. In the presence of Al, molar activity ratios of Ca/Al and {dollar}rm Ca/Sigma asb{lcub}Al mono{rcub}{dollar} were the best predictions of main root growth. Ferron reagent was likely overestimated reactive Al and failed to exclude Al complexed with SO{dollar}sb4sp=.{dollar} Main and lateral root length were higher when Ca was supplied as CaSO{dollar}sb4,{dollar} but Ca concentration in solution was more important than the Ca source in alleviating Al toxicity. Magnesium complemented but could not replace Ca in alleviating Al toxicity. The contribution of different roots on total root length was affected by pH, Al, Ca, Mg, B and Zn. |
