RELATIONSHIP BETWEEN THE CATION ANION UPTAKE AND THE RELEASE OF PROTONS BY ROOTS OF RED-CLOVER

Red clover was cultivated in Mitscherlich pots on a brown podzolic soil. Besides a low N rate at the beginning of the experiment, the clover received only symbiontically fixed N. Soil pH dropped under clover from 7.2 to 4.5 during a period of 14 mo. During this time 7 cuts were obtained. In a parallel pot experiment with rye-grass grown on the same soil and under the same environmental conditions but supplied with NH4NO3 after each clipping, no drop in soil pH. In the aerial plant parts of clover the cation excess was high and amounted to .apprx. 60% of the H+ quantity required for the decrease in soil pH from 7.2 to 4.5. Evidently, the cations taken up in excess were electrostatically balanced by an equivalent amount of protons secreted by the roots into the soil. The alcalinity assessed in the upper plant parts of clover was approximately equivalent to the cation excess. Apparently, the H+ release from roots resulted in an alkalinization in the plant cells which in return led to a synthesis of organic anions being equivalent to the amount of H+ released.