Net Nitrogen Mineralization in Natural and Drained Fen Peatlands in Alberta, Canada
1996
Humphrey, William D. | Pluth, Donald J.
The lowering of water tables by ditching in boreal, minerotrophic peatlands modifies soil environmental factors that regulate nitrogen mineralization-immobilization. Long-term responses of nitrogen mineralization to drainage may vary depending on substrate pH and chemical composition. Research has shown that peat drainage and N fertilization of boreal Histosols increase growth rates of coniferous trees. This study was conducted to determine the response of N mineralization to lowering of water tables and to relate N mineralization to selected soil properties. Net N mineralization rates were determined by in situ incubation of peat samples in paired natural and drained areas of midcontinental boreal fens representing a gradient in soil pH from 4.0 to 7.2. Analysis of variance of N mineralization revealed a significant interaction between soil pH and drainage category. At pH 4.0, net N mineralization did not differ between the natural and drained areas. At the intermediate pH levels, net N mineralization in the natural areas was up to two times that of the drained areas. At pH 7.2, the N mineralization relationship between the two areas was reversed. Post-ditching increases in peat bulk density in the sites of intermediate pH correlated with higher volumetric water content and lower concentration of inorganic N compared with the natural areas. The concentration of inorganic N decreased by about 50% with soil depth to 30 cm in both the natural and drained areas. Although small for all soils, net NO⁻₃ production was not influenced by the pH level or drainage category from 7 to 30 yr after ditching.
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