Einfluß einer mineralischen und symbiontischen Stickstoffernährung auf Protonenabgabe der Wurzeln,Phosphat-Aufnahme und Wurzelentwicklung von Rotklee

Influence of mineral and symbiotic nitrogen nutrition on proton release of roots, phosphorusuptake and root development of red clover Red clover was cultivated in pots containing a loamy sand soil of low buffer capacity. Nitrogen supply was either NH₄NO₃ and Ca(NO₃)₂ in the mineral treatment or Rhizobium fixed N₂ in the symbiotic treatment. During six cuts the plants decreased the pH of the soil from 7.6 to 6.0 in the mineral treatment and to 5.2 in the symbiotic treatment. Both treatments yielded the same amount of shoot dry matter per pot. The N₂-fixing red clover produced more root fresh weight associated with larger root length, root surface, and root density per pot compared with plants grown with mineral nitrogen. Due to stronger soil acidification and better root growth N₂-fixing red clover was able to exploit the rock phosphate component from a partially acidulated P-fertilizer to a higher degree than NH₄NO₃ or Ca(NO₃)₂ fed plants. The proton release of symbiotically grown plants could be accounted for by mineral cation excess (difference of cation and anion uptake) in shoots and roots by only 68%. It is therefore assumed that the excess of H⁺ released was accompanied by a release of anions.