Einfluß des Zeitpunktes der K-Düngung auf die Dynamik des nach der Gülledüngung spezifisch gebundenen NH4-N der Tonminerale*

Influence of the time of K fertilization on the dynamics of NH₄-N fixed by clay minerals after slurry application In a pot experiment with topsoil and subsoil of a luvisol derived from loess the influence of the time of K fertilization on the fixation of NH₄-N supplied with slurry as well as on the leaching and the availability of NH₄-N fixed by clay minerals after slurry application was investigated. The following results were obtained: In both soils K fertilization before slurry application resulted in a reduced fixation of the added NH₄⁺.In the topsoil 8 % of the NH₄⁺ supplied with the slurry could be detected in spring as nonexchangeable NH₄⁺ when slurry was added in October and 13 % when slurry was added in January in the treatment K after slurry, when in the treatment K. before slurry the NH₄⁺ fixed after slurry application had been mobilized totally. In the subsoil 45 % of the NH₄⁺ fixed after slurry application in October were mobilized until spring in the treatment K before slurry and only 20 % in the treatment K after slurry. When slurry was applied in January 30 % and 12 %, respectively, were mobilized. In spite of the reduced nitrogen leaching in the treatments K after slurry yield and N uptake of grass were lower as compared to the treatments K before slurry.