EXPERIMENTAL MICROCOSM STUDY OF THE ROLE OF LUMBRICUS-TERRESTRIS (OLIGOCHAETA, LUMBRICIDAE) ON NITROGEN DYNAMICS IN CULTIVATED SOILS

A laboratory experiment using microcosms was carried out to assess the influence of earthworms on the dynamics of nitrogen derived from organic matter applications in cultivated soils. The study was performed with the anecic Lumbricus terrestris fed on N-15-labelled litter (N*) of rye-grass for 85 days. The gross consumption of rye-grass litter by L. terrestris was estimated to be 13 mg d.m. g-1 f.m. day-1, while, when the mass loss from litter in the microcosms without worms was deducted, the net consumption was only of 2.4 mg d.w. g-1 f.m. day-1 of earthworms. The total N-15 released from the litter into the soil was 3 times larger in microcosms with, than without, worms (0.63 mg day-1 vs 0.20 mg day-1, respectively). This gives a daily output flux of 0.13 mg N* g-1 live worm day-1. The rate of incorporation of N-15-labelled litter into the earthworm was estimated to be 0.14 mg N* per live worm day-1, which indicates a nitrogen renewal of 10% in the earthworm biomass in 85 days. The whole N* input from earthworm, into the soil reached to 76 mug g-1 day-1 f.m., 28% of this was due to N excretion (21 mug N g-1 f.m. day-1).