Participation of silicon in cation‐anion balance as a possible mechanism for aluminum and iron tolerance in some gramineae

Abstract

Silicon (Si) has been suggested as a factor in aluminum (Al) tolerance of some species of the gramineae when grown on acid soils. Silicon concentrations are generally much higher in monocot plants than in dicot plants, and the phenomenon is related to the fact that mineral cation:mineral anion uptake ratio is much higher in dicots than in monocots. When large amounts of anionic Si, supposedly as silicate (SiO₄ ⁴⁻), participate in cation‐anion balance to add to the excess of anion uptake, equivalent amounts of hydroxyl ions should be expelled from roots, which can increase rhizosphere pH and decrease uptake of Al and iron (Fe). The magnitude of OH⁻ released by roots for a 5000 kg/ha crop with an excess uptake of 1% Si can be equivalent to 357 kg lime per hectare. This could be very significant in decreasing Al and Fe uptake from acid soils when localized in the rhizosphere. Success of agriculture on highly acid soils may be enhanced by use in a rotation of crops and cultivars that have the ability to accumulate Si.