Summary
Plants that absorb nitrogen as NO3 − tend to raise the pH in the rhizosphere. Those absorbing nitrogen as NH4 + or N2 lower the pH. The change in pH near the root surface may be calculated approximately from the H+ or HCO3 − efflux and radius of the root; and the pH buffering capacity, moisture content, initial pH and pCO 2 of the soil. An accurate equation, solved numerically, also takes account of root hairs, mass flow and slow acid-base reaction in the soil. The pH at the root surface will often differ from the pH a few mm away by 1–2 units.
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Nye, P.H. Changes of pH across the rhizosphere induced by roots. Plant Soil 61, 7–26 (1981). https://doi.org/10.1007/BF02277359
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DOI: https://doi.org/10.1007/BF02277359