From 1999 until 2002 fluxes and transformations of N and P
were measured in an intensively managed grassland on
peat soil with shallow (~ 40 cm) groundwater level. Measurements included
inputs of N and P via fertilizer and animal manure, outputs via herbage, denitrification,
mineralization, discharge, run-off, and concentrations of N, P and Cl in the
soil solution at various places accros the field. The soil consisted of a man-made topsoil of
about 30 cm, oxidized eutrophic peat (0.3-1 m), reduced
eutrophic peat (1-3 m), calcareous marine deposits containing light and heavy
clay (3 – 9 m) and Pleistocene sands (> 9 m). The presence of the eutrophic
peat layer had a distinct impact on the nutrient dynamics of the peat soil,
i.e. it largely governed the composition of the soil solution and was a
considerable contributor of nutrient leaching to the adjacent surface water
(Table 1).
Table 1. Average fluxes (kg ha-1y-1) in an intensively
managed peat soil in The
| | N | P | Cl |
IN | Mineral ferilizer | 159 (17-20) | 0 | 11 |
| Atmospheric deposition | 31 (8-9) | | 71 |
| Slurry application | 159 (17-20) | 22 (22-34) | 81 |
| Dung and urine of grazing animals | 87 (911) | 9 (9-14) | 33 |
| Supply from peat layer | 8 (8-27) | 3 (33-82) | 120 |
| Mineralization of soil organic matter | 210 (17-31) | 10 (2-14) | <1 |
OUT | Mown grass | -231 | -24 | -79 |
| Grazing | -100 | -10 | -79 |
| Denitrification | -210 | 0 | 0 |
| NH3 volatilization | -20 | 0 | 0 |
| Leaching to surface water | -38 | -6 | -170 |
| Groundwater recharge | -4 | -0.4 | <1 |
SUM | | 51 | 4 | -12 |
The presence of shallow groundwater and eutrophic peat facilitate large biochemical processes (mineralization, nitrification and denitrification) and thereby veile direct relations between agricultural management and surface water quality.