Vorräte und Nachlieferung an Mineralstickstoff im Boden eines Meliorationsexperiments zu Kiefer

The influence of soil amelioration procedures on the content and production of mineral nitrogen in the soil of a formerly litter raked pine stand in Upper Palatia In 1964 a soil amelioration experiment was started in a 87-year-old, Scots Pine stand of site class III.8., situated in the growth district ?Oberpfälzer Jurarand”?, East Bavaria. The soil, degraded in former times by litter removal, is a podsolic pseudogley, derived from cretaceous sediments with diluvial loess depositions. The trial comprised of the following treatments: NPKCaMg-fertilization, the N-input was repeated three times (I- ?Volldüngungsvariante”?); PKCaMg-fertilization and tillage to a depth of 20 cm (II–?Fräsvariante”?); PKCaMg-fertilization, tillage and underplanting of the perennial legume Lupinus polyphyllus (III-?Lupinenvariante”?); control (O). In the 15^th vegetation period after the beginning of the experiment and 6 years after the last N-fertilization respectively, the effects of these amelioration procedures on the content and production of mineral nitrogen (incubation in the field) were investigated. The mean N-net mineralization rate in the upper soil increased in the following sequence: control 100% – Fräsvariante 114% – Volldüngungsvariante 400% – Lupinenvariante 628%. A significant linear correlation could be detected between N_min-production and the nitrogen content in pine needles; methodical problems of incubation however caused an underestimation of the absolute mineralization level on all treatments. The nitrification was promoted by N-fertilization and lupine treatment. On the ?Volldüngungsvariante”? the N_min-production rose in the organic layer, on the ?Lupinenvanante”? in the mineral soil. Characteristic of lupine treatment were a low actual content of mineral nitrogen at the beginning of vegetation period and a rapid mineralization during springtime. The highest actual N_min-contents in the upper soils were generally observed in the summer. On the ameliorated treatments a significant decrease occurred in the late summer, followed by a small increase in the autumn.