K. Granlund et al. Agriculture, Ecosystems and Environment 80 2000 1–13 11
areas: dairy production and thus grass cultivation dom- inate in the northern areas, whereas cereal production
is more common in the southern areas. Clay soils dom- inate in the southern areas, whereas more permeable
soils are common in the northern areas. This is also one reason for higher losses in the northern areas. The
nitrate loss was estimated to have decreased to some extent in all the study areas, although the changes were
rather small 3–14, Table 6.
4. Discussion
The purpose of using a deterministic simulation model in this study was to assess relative changes in
nitrate losses caused by changes in management prac- tices, in order to provide rapid feed-back information
for decision-making. Validation of the model against observed time series over a wide range of soils, crops
and management practices was impossible, e.g., due to the lack of measured data. More field data is needed
to improve the model parametrisation of crop growth in Finnish conditions and to evaluate model results es-
pecially in the case of manure application.
The results from these model calculations are not readily comparable to actual field or lysimeter mea-
surements on N leaching. This is due, e.g., to the fact, that the modelled profile and the standard management
practices were rather simple because of computational restrictions. Moreover, the history of the experimental
fields provides site-specific initial values of mineral N in the soil, and crop rotation is often a factor in such
studies. In the model runs a standard set of initial val- ues was used, and in order to be able to compare the
long-term leaching values of different crops and soils, no crop rotation was envolved. However, in the next
the results of model calculations are compared with existing field data on N leaching in case studies where
similar crops and soils were used.
Yläranta et al. 1993 have studied leaching of ni- trogen from fallow, barley and grass ley in different
soils in a 4-year lysimeter experiment in Jokioinen, southern Finland. The leaching of total nitrogen of
which nitrate-N was predominant from barley was approximately 20 kg ha
− 1
for the 4 years period in clay soil and approximately 115 kg ha
− 1
in sand soil. In this study the amount of inorganic nitrogen fertiliser
was 100 kg ha
− 1
per year N. The modelled nitrate leaching for barley in Yläneenjoki was of the same
order and was higher in sandy soils than in clay soils. Field experiments in Finland and in Sweden e.g.,
Jaakkola, 1984; Bergström and Jarvis, 1991 have shown that leaching losses from cereals are rather
small if recommended, moderate amounts of inor- ganic fertilisers are used. Bergström and Jarvis 1991
used the SOILSOIL-N model to predict nitrate leach- ing from arable clay soil at application rates of 0,
100 and 200 kg ha
− 1
per year N in south-west Swe- den. The long-term mean yearly leaching losses at
different nitrogen application rates were reasonably well estimated by the model. Leaching losses were
rather small in the treatment with 100 kg ha
− 1
per year N, but doubling the applied fertiliser rate to
200 kg ha
− 1
per year N increased the leaching from 6.6 to 43.1 kg ha
− 1
per year N. The interview data of the present study indicated that, in some cases,
farmers actually have applied higher rates than the recommended ones on their fields. This was taken
into account in the model calculations, and higher input values of N were tested in order to evaluate
the risk of leaching in these cases. The calculated leaching values increased if fertilisation exceeded the
recommended rates.
According to model results a situation where slurry is applied in autumn in addition to inorganic spring fer-
tiliser causes the highest leaching values. The effect of spreading time on N leaching was also clearly demon-
strated in a lysimeter trial by Kemppainen 1995. The effects of soil type, spreading time and use of a nitrifi-
cation inhibitor on the leaching and uptake of nitrogen and phosphorus from cow slurry and fox manure were
studied in lysimeters in northern Finland. Nitrogen leaching from barley was lowest with spring applica-
tion and highest with applications in September.
The approach used in this study, i.e., using a one-dimensional soil profile model combined with
spatial data, produces regional loss estimates which are not comparable to the actual losses from the river
basins. This is caused by the fact that, 1 this model does not contain overland flow processes, groundwa-
ter discharge and channel and pond processes, 2 no vertical soil structures were included in the model cal-
culations due to lack of data, and 3 only agricultural fields where interviewed data existed were modelled,
and no other land use classes. Thus the upscaled model results for the study basins cannot be compared
12 K. Granlund et al. Agriculture, Ecosystems and Environment 80 2000 1–13
to observations of nitrate concentrations and fluxes at the outlets of the basins. This allows only the use of
relative differences instead of absolute values. The calculated regional reductions in nitrate loss
see Table 6 were mainly caused by reductions in fer- tilisation rates see Table 5 . In Lepsämänjoki and
Yläneenjoki spring cereals are the most common crops 59 and 65 of the total cultivated area, respectively.
Thus reduction of fertilisation of spring cereals gov- erned the changes in nitrate leaching. The mean reduc-
tion of fertilisation rates for spring cereals was 4 in Yläneenjoki and 7 in Lepsämänjoki. Therefore, the
reduction of nitrate leaching was lower in Yläneen- joki than in Lepsämänjoki. Another reason for lower
reduction in nitrate leaching in Yläneenjoki compared to Lepsämänjoki is possibly the higher livestock den-
sity pigs and poultry Table 1 in Yläneenjoki. No remarkable change was observed in animal densities,
and thus nitrogen input was dominated by manure and the reduction in total nitrogen input was not as high as
in Lepsämänjoki. In Lestijoki the amount of applied slurry has increased on average 30.5 m
3
ha
− 1
in 1995 and 35 m
3
ha
− 1
in 1997. Thus, the reduction in nitrate leaching 3 was clearly lower than in other areas.
However, the interview data for Lestijoki was not com- plete for the years 1994 and 1995, which may explain
some of the discrepancies compared to the other areas.
5. Conclusions
