Hydroxyl release by maize (Zea mays L.) roots under acidic conditions due to nitrate absorption and its potential to ameliorate an acidic Ultisol

Purpose

Hydroxyl ion release by maize (Zea mays L.) roots under acidic conditions was investigated with a view to develop a bioremediation method for ameliorating acid soils in tropical and subtropical regions.

Materials and methods

Two hydroponic culture experiments and one pot experiment were conducted: pH, nitrogen state, and rhizobox condition, which investigated the effects of different nitrogen forms on hydroxyl release by maize roots under acidic conditions.

Results and discussion

The pH of the culture solution increased as culture time rose. The gradient of change increased with rising NO₃ ^?/NH₄ ⁺ molar ratios. Maize roots released more hydroxyl ions at pH 4.0 than at pH 5.0. The amount of hydroxyl ions released by maize roots at a constant pH was greater than those at a nonconstant pH. Application of calcium nitrate reduced exchangeable acidity and increased the pH in an Ultisol rhizosphere, compared with bulk soil. The increasing magnitude of soil pH was greater at higher doses of N. The absorption of NO₃ ^?–N increased as the NO₃ ^?/NH₄ ⁺ molar ratios rose, which was responsible for hydroxyl ion release and pH increases in culture solutions and rhizosphere.

Conclusions

Root-induced alkalization in the rhizosphere resulting from nitrate absorption by maize plants can be used to ameliorate acidic Ultisols.