Measurement of pH at the root surface of red clover (Trifolium pratense) grown in soils differing in proton buffer capacity

Summary Measurements of pH were made at the root surface of Trifolium pratense, using Sb electrodes. Nodulated plants were grown in rhizotrones on a sandy soil free of carbonate and on a clay soil rich in carbonate. In the sandy soil, pH at the surface of root laterals was about 1 unit lower than in the bulk soil. The lowest pH values were found at the root tips. In the calcareous soil, pH measured at the root surface did not differ from pH in the bulk soil. This soil had a much higher H⁺ buffer capacity than the sandy soils. It seems likely that H⁺ ions excreted from the roots grown in the calcareous soil were directly neutralized by soil carbonate.