The effect of compost fertilization compared with mineral fertilization on N leaching to the groundwater was investigated in six plots of a long-term field experiment and a lysimeter station on a Molli-gleyic Fluvisol (WRB) near Vienna, Austria. The plots investigated included two treatments with compost fertilization (16 and 23 t ha -1 y -1 , respectively, on average of 11 y), two treatments with mineral N fertilization (41 and 56 kg N ha -1 y -1 , respectively), and two treatments with combined fertilization (9 t compost + 56 kg N ha -1 y -1 and 23 t compost + 22 kg N ha -1 y -1 , respectively). Nitrogen leaching to the groundwater as determined using ceramic suction cups was not increased after 11 y of compost fertilization with higher amounts than used in practical farming (23 t ha -1 y -1 , corresponding to an annual input of 205 kg N tot ha -1 ) as compared to mineral fertilization under the conditions of the experiment. Even intensive N mineralization during a 4-month period of bare fallow did not cause pronounced differences between the fertilization treatments. The results suggest that in the pannonic climate, compost fertilization does not pose a risk for groundwater eutrophication on the medium term.

In the North Tyrolean Limestone Alps a site was investigated over a four-year period (1998-2001) in order to assess the nitrogen saturation status, the nitrogen budget (quantification of the net uptake of nitrogen by the canopy and of the nitrogen mineralization, nitrogen uptake from roots and N2O emission rates, proof of the origin of nitrate in the soil water with stable isotope analyses), and the effects of the actual nitrogen input on ground water quality. The main goals were to quantify the nitrogen input rate, the nitrogen pools in above-ground and below-ground compartments, nitrogen turnover processes in the soil as well as the output into the groundwater and into the atmosphere. The findings are based on continuous and discontinuous field measurements as well as on model results. While nitrogen input exceeded the Critical Loads of the WHO (1995), nitrogen deficiency and nutrient imbalances were verified by needle analyses. The atmospheric input of inorganic nitrogen was higher than the nitrogen output in 50 cm soil depth. A tracer experiment with 15N helped to prove that not more than half of the applied nitrate could be discharged. This allows the conclusion that nitrogen is stored in the system and that the site cannot yet be said to be saturated with nitrogen. The same result was also obtained by modelling. In addition, it was proved that the nitrogen discharge did not stem from deposition but from processes within the system.

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The water balance for the site Mühleggerköpfl in the North Tyrolean Limestone Alps has been established to a soil depth of 50 cm. The evaporation amounts to 42% and deep percolation is 58% of the precipitation. The surface runoff was negligible and therefore the according nitrate fluxes as welL Soil water analysis revealed mean nitrate concentrations of 3 to 15 mg NO3 L(-1), depending on soil depth. The nitrate concentrations at 50 cm soil depth and the associated percolation rates led to NO3-N outputs of 15.9 kg NO3-N ha(-1) in the year 1999 and 7.9 kg NO3-N ha(-1) in the year 2000.

Soil organic ma�er and its turnover rate are key parameters for agricultural management practice as well as for environmental issues. In a field experiment comparing organic (compost) and mineral fertilisation and combinations of both the amount of inorganic nitrogen in the soil and the nitrogen uptake by the plants were measured. Considering these data and the fertilisation practice the net N-mineralisation during the vegetation periods 1996-2001 was estimated for six fertilisation treatments. Simultaneously the nitrogen dynamics in the soil were calculated using the STOTRASIM model, which takes into account four soil organic ma�er pools of different turnover rate. A close relation was found between the amount of a slow decomposable fraction and the net N-mineralisation during the vegetation period. composting plant of the City of Vienna was used. The compost raw material consisted of sourceseparated organic waste, which included organic household waste and yard trimmings at a 2:3 ratio. The compost was produced in an open windrow process with regular turning using front-end loader and windrow turner.The amount of inorganic nitrogen in the soil (NO 3 -N + NH 4 -N for the depth of 0-90 cm) was measured periodically in each plot and the yield and the nitrogen uptake by the plants were determined annually. For the six plots investigated in detail the net-N-mineralisation during the vegetation periods 1996-2001 is calculated using the following equation assuming that inorganic N-input from the atmosphere is compensated by gaseous losses (Table 1) ModellingThe water fluxes in the soil and plant growth are calculated with the deterministic simulation model SIMWASER (Stenitzer 1988) and the nitrogen dynamics in the soil and accordingly the losses of nitrate to the groundwater are calculated with STOTRASIM (Feichtinger 1998). The models describe one-dimensional, vertical flow of water and nitrate-nitrogen within a soil profile, neglecting interflow and preferential flow.SIMWASER simulates the water balance for a soil profile and the crop yield of any number of crop rotations and years on a daily basis, provided that daily weather records are available. The water balance and the growth of plants are interrelated by the physiological interaction of assimilation and transpiration. Potential assimilation and therefore potential plant growth occurs as long as the water supply towards the stomata can meet the potential transpiration loss. The potential growth rate is specific to each crop and depends mainly on air temperature and global radiation. The potential plant production rate and the proportion of actual transpiration to the potential one calculate actual plant growth. The potential evapotranspiration is calculated according to the Penman-Monteith-for- Szeicz et al. 1969, Thom et Oliver 1977 and the potential transpiration is deduced from the potential evapotranspiration. The actual transpiration is the amount of water, which can be withdrawn by the roots from the soil and is less equal to the potential tra...