Nitrogen mineralization rate was studied in grazing trials with three diffe
rent stocking rates (0, 3, 10 sheep ha(-1)) in two man-made salt marshes, v
iz. a Puccinellia maritima-dominated low salt marsh and a high salt marsh d
ominated by Festuca rubra. Mineralization rates were derived from the amoun
ts of mineral N which accumulated in situ during six-week incubation period
s in tubes containing undisturbed soil cores from the upper 10 cm soil laye
r. The annual rates of net N mineralization were significantly higher in th
e better drained, high salt marsh (71 - 81 kg ha(-1) yr(-1)) than in the lo
w salt marsh (39-49 kg ha(-1) yr(-1)). High amounts of belowground litter a
ccumulated in the low salt marsh due to frequent water logging. Both IN min
eralization and nitrification rate were negatively correlated with soil wat
er content. In the Puccinellia maritima salt marsh, grazing had neither an
effect on N mineralization rates during any of the incubation periods nor o
n annual mineralization rates. In the Festuca rubra salt marsh, N mineraliz
ation rates increased earlier during spring at the intensively grazed site
than at the moderately grazed and the ungrazed site. N mineralization and n
itrification rates were significantly higher at the ungrazed site: than at
the intensively grazed site during the period of peak net IN mineralization
from the end of April until mid-June. Although sheep grazing affected the
seasonal pattern of N mineralization in the high marsh, grazing did not aff
ect the annual rate of net N mineralization.