Net and gross nitrogen mineralization in drained and reflooded fen soils

One purpose of new land use concepts for degraded fens (organic soils with high N content) is the reduction of the mineralization process due to very high groundwater levels. However, knowledge of nitrogen mineralization proc ess (net and gross) in degraded fen soils affected by reflooding is very sm all. Therefore, the objectives of our study were (a) to evaluate the suitab ility of N-15 pool dilution method for measurements of gross mineralization rates in degraded fen soils and (b) to investigate how the reflooding of a degraded fen affects the net and gross nitrogen mineralization in a shortt erm incubation experiment. The usability of the N-15 pool dilution method w as diminished by the low recovery of the applied (NH4+)-N-15 at time zero. The recovery of the added (NH4+)-N-15 in the extractable soil NH4+ pool was only 13.5% for the drained soil and 59.6% for the reflooded soil. However, the gross mineralization rates were similar for both soils and exceeded al ways the net rates substantially. The cumulative net mineralization rate wa s higher for the reflooded soil (1.58 mu g N*cm(-3)*d(-1)) than for the dra ined soil (-0.67 mu g N*cm(-3)*d(-1)). Differences between the two soils we re also found in the nitrification intensity and the loss of N-15. This was probably one reason for the higher net mineralization rate in the refloode d soil.