Root-induced changes in the rhizosphere of plants. I. pH changes in relation to the bulk soil

The rhizobox system offers quantitative information concerning the pH changes and the range of the rhizosphere. Changes in pH values around the roots (barley and soybean) were investigated using a rhizobox. The results indicated that the pH values increased near the roots in soils with a low pH of the bulk soil (about 5). Changes of pH were as much as 2 units, compared to the bulk soil. Conversely, the rhizosphere pH decreased by about 2 units in soils with a bulk soil pH of 7. A slight decrease in the rhizosphere pH was observed in soils with a bulk soil pH of 8.4. The ability of soybean roots to influence the pH was larger than that of barley. No effect of N -serve on the pH of the rhizosphere and bulk soil was observed when ammonium sulphate was applied. These results suggest that the extent to which the rhizosphere pH can differ from that of the bulk soil depends more on the plant species and initial bulk soil pH than upon N-fertilizer source or N-level.