Soil nitrogen concentrations in a restored sedge meadow wetland as affected by the application of high C:N amendments

Invasive perennial species are frequently a barrier to native plant establishment in fertile sedge meadow wetland restorations. Amending soils with high carbon-to-nitrogen (C:N) materials may deplete nitrogen (N) and limit the establishment of invasive species, although the effectiveness of such amendments at depleting soil N in restored wetlands is largely unknown. Therefore we incorporated four high C:N materials (cedar, white pine, and red oak sawdust, as well as sucrose) into the soils of nonvegetated plots in a restored sedge meadow wetland and measured soil ammonium-N and nitrate- N in relation to nonamended control plots over a 25-week period. All amendments depleted nitrate-N concentrations equivalently (67%-100%), although both the timing and the duration of this depletion varied among amendments. White pine sawdust was most effective, depleting nitrate-N for the entire 25 weeks. Sawdust from red oak and cedar depleted nitrate-N after 5 and 13 weeks, respectively. Lowered nitrate-N concentrations then persisted for the remaining 20 weeks in the red oak treatments, while the effects of cedar were short-lived (8 weeks). Sucrose depleted nitrate-N for 13 weeks. No amendment depleted ammonium-N concentrations, although cedar sawdust caused initial ammonium-N concentrations to increase by 300%-700%. Based on our findings, white pine sawdust will be more likely to deplete N effectively during the establishment of sedge meadow wetlands. It is unknown, however, if this depletion will suppress invasive perennials long enough to allow desired native species to establish a closed canopy and take up nitrogen, thereby limiting the chances of future invasions.