CHANGES IN SOIL ORGANIC-MATTER AND NET NITROGEN MINERALIZATION IN HEATHLAND SOILS, AFTER REMOVAL, ADDITION OR REPLACEMENT OF LITTER FROM ERICA-TETRALIX OR MOLINIA-CAERULEA

The effects of different litter input rates and of different types of litter on soil organic matter accumulation and net N mineralization we re investigated in plant communities dominated by Erica tetralix L. or Molinia caerulea (L.) Moench. Plots in which the litter on the soil h ad repeatedly been removed were compared with plots in the same plant community in which litter had been added to the soil. In another treat ment, litter was removed and replaced by litter from the other plant c ommunity. Net N mineralization was measured in situ after 5 years. Les s soil organic matter and soil N was found in plots in which litter ha d been removed, compared with control plots, or plots to which litter had been added, but these differences were significant for the Erica s p. soils only. Plots in which litter had been replaced and control plo ts did not differ significantly in the amount of soil organic matter. However, in both plant communities, the differences agreed with the fa ster decomposition rate of Molinia sp. litter compared with Erica sp. litter. The gravimetric soil moisture content was correlated positivel y with the amount of soil organic matter, both in the Erica sp. soils and the Molinia sp. soils. Net N mineralization rates (g N m-2) differ ed significantly between treatments for Erica sp. soils but no for Mol inia sp. soils. For Erica sp. soils, net N mineralization rates increa sed with increasing amounts of soil organic matter and soil N. Replaci ng the litter with Molinia sp. litter (which differs in chemical compo sition) had no clear additional effect on the net N mineralization rat e.