8 K. Granlund et al. Agriculture, Ecosystems and Environment 80 2000 1–13
The spatial database contained the corner coordi- nates and the soil type and management data for the
field parcels. To calculate the regional losses and their changes, the loss estimates for each field parcel
were summed up separately for all farms in the four study areas for the years 1995 and 1997. Average
regional nitrate leaching in kg ha
− 1
per year was then calculated for both years and for all the study
areas.
3. Results
3.1. Changes in actual fertiliser use The Agri-Environmental Support Scheme sets
crop-specific limits for the use of nitrogen fertilisers Table 4. According to the interview data, a general
reduction in the fertilisation rates to meet these limits has taken place in all the study areas Table 5. For ce-
reals, the greatest reductions were observed for winter wheat in the southern areas ca. 25. The amount
of fertiliser applied for grass showed a slight increase in Lepsämänjoki and Lestijoki. In Lestijoki, this was
due to an increase in slurry application. For the other crops the reductions in fertiliser use were modest, but
in general the reductions during these years continue the general decreasing trends in the use of nitrogen
fertilisers during the 1990s Pirttijärvi, 1998.
Table 5 Average crop-specific nitrogen fertilisation rates in the study areas in 1995 and 1997 based on interviews with farmers
a
Crop Average nitrogen fertilisation rates kg ha
− 1
per year N Yläneenjoki
Lepsämänjoki Lestijoki
Taipaleenjoki 1995
1997 1995
1997 1995
1997 1995
1997 Spring wheat
116 105
111 105
– –
– –
Winter wheat
b
145 109
151 115
– –
– –
Barley 86
88 104
93 78
74 87
73 Oats
85 80
95 91
74 81
83 71
Rape 95
99 114
106 –
– –
– Grass for silage
162 173
132 161
194 178
145 132
Grass for hay 107
105 89
122 88
118 125
123 Sugarbeets
126 136
– –
– –
– –
Potato 76
45 –
– 66
67 –
–
a
Blank entries in column indicate few or no observations.
b
For winter wheat, the periods 1994–1995 and 1996–1997 are included. Table 4
The crop-specific nitrogen fertilisation rates set by the Finnish Agri-Environmental Support Scheme modified from the Ministry
of Agriculture and Forestry, 1995
Crop Nitrogen fertilisation
kg ha
− 1
per year N Fodder cereal
90 Spring wheat
100 Winter wheat, autumn application
20 Winter wheat, spring application
100 Winter rye, autumn application
20 Winter rye, spring application
100 Oilseed crops
100 Sugarbeet
120 Potato
60–80 Silage
180 Hay
90 +60
a a
In case of second harvest.
3.2. Calculated nitrate losses The mean annual nitrate losses were calculated on
the basis of the 10-year daily output of the model runs. In this calculation, the inter-annual variation caused
by fluctuating climatic conditions could mostly be ig- nored. The results represent potential long-term nitrate
losses and their changes, assuming that cultivation is continued for a long period according to current man-
agement practices.
The calculated mean annual nitrate leaching varied considerably between different crops and soils Fig. 5.
K. Granlund et al. Agriculture, Ecosystems and Environment 80 2000 1–13 9
Fig. 5. Relative calculated leaching of nitrate from silty clay Soil 2, Table 2 in the Yläneenjoki study area cultivated with
different crops with fertilisation rates according to the Finnish Agri-Environmental Support Scheme a. Relative calculated leach-
ing of nitrate from barley fields in different soils in the Yläneen- joki study area fertilisation 100 kg ha
− 1
per year N b. The value 1 represents the maximum nitrate leached. See Table 2 for
a description of the soil types.
The highest amounts of nitrate were in most cases leached from winter cereals and sugarbeet. In the case
of winter cereals this was mainly caused by autumn application of either inorganic or organic fertiliser. The
reason for high nitrate leaching in the case of sugar- beet cultivation was the high use of nitrogen fertiliser
120–200 kg ha
− 1
per year N. The calculated leaching of nitrate was strongly dependent on soil type Fig. 5.
Leaching was usually highest in silt loam soils Soils 6–8, see Table 2 and lowest in clay soil Soil 1, see
Table 2. The differences were mainly due to differ- ent water retention characteristics and thermal condi-
tions, which affect water flow and mineralisation and denitrification rates.
No substantial differences were found in crop- specific nitrate leaching between Lepsämänjoki,
Fig. 6. Relative calculated leaching of nitrate from barley, potato and winter rye fields in different study areas mean of all soil types
with fertilisation rates according to the Finnish Agri-Environmental Support Scheme. The value 1 represents the maximum nitrate
leached.
Yläneenjoki and Taipaleenjoki. In Lestijoki, however, the precipitation Fig. 4 and thus the water flow from
the bottom of the soil profile was lower than in the other areas. This caused lower nitrate leaching values
in Lestijoki than in the other areas Fig. 6, because in the model the calculated nitrate leaching is governed
by deep percolation.
Differences in nitrate leaching were substantial for different fertilisation rates Fig. 7. The relationships
between the calculated leaching and fertilisation rates were non-linear for many crop-soil combinations,
showing exponential features. The calculated leach-
Fig. 7. Relative calculated leaching of nitrate from barley fields in the Yläneenjoki study area for different inorganic fertilisation
rates in silty clay Soil 2, Table 2. The value 1 represents the maximum nitrate leached.
10 K. Granlund et al. Agriculture, Ecosystems and Environment 80 2000 1–13
Fig. 8. Relative calculated leaching of nitrate from barley fields in different study areas in silty clay Soil 2, Table 2. Spring fer-
tilisation: inorganic fertiliser 140 kg ha
− 1
per year N or a combi- nation of inorganic fertiliser 100 kg ha
− 1
per year N and slurry 40 kg ha
− 1
per year soluble N. The value 1 represents the max- imum nitrate leached.
ing values were higher if manure was used in addition to inorganic fertiliser compared to the case with pure
inorganic fertilisation, even if the total amounts of applied soluble nitrogen were equal Fig. 8. This is
due to the fact that in addition to the soluble inor- ganic nitrogen, manure also contains organic fractions
which in the long run can be mineralised in the soil. Manure application in autumn resulted in higher ni-
trate leaching than after spring application, but both leachings were higher than that caused by only inor-
ganic fertilisation Fig. 9. The reason for high nitrate leaching after autumn manure application is that in
autumn the uptake of nitrogen by plants has ceased, and drainage of water increases. Moreover, minerali-
sation of organic nitrogen may continue during early autumn. Nitrate leaching increased in all areas if fer-
tilisation rates exceeded the rates set by the Support Scheme. This can be seen in Fig. 10, which shows
calculated relative leaching from barley in all areas for two different fertilisation rates inorganic fertiliser
100 and 140 kg ha
− 1
per year N, silty clay. 3.3. Regional changes
The calculated average nitrate losses were higher in Lestijoki and Taipaleenjoki than in the southern areas
Table 6. The main reason for this was the clear dif- ference in the production structure between the two
Fig. 9. Relative calculated leaching of nitrate from barley fields in the Yläneenjoki study area in silty clay and silt loam Soils 2 and
7, Table 2 with different fertilisation schemes. Fert. 1=inorganic fertiliser 140 kg ha
− 1
per year N in spring. Fert. 2=inorganic fertiliser 100 kg ha
− 1
per year N in spring+slurry 40 kg ha
− 1
per year soluble N in spring. Fert. 3=inorganic fertiliser 95 kg ha
− 1
per year N in spring+slurry 50 kg ha
− 1
per year soluble N in autumn. The value 1 represents the maximum nitrate leached.
Fig. 10. Relative calculated leaching of nitrate from barley fields in different study areas for two different rates of inorganic fertiliser
in silty clay Soil 2, Table 2. The value 1 represents the maximum nitrate leached.
Table 6 Relative calculated nitrate losses in 1997 the value 1 representing
the maximum nitrate leached and changes in these losses between 1995 and 1997 in the study areas
Area Relative nitrate loss
1997 Change 1995–1997 per cent
Lepsämänjoki 0.3
− 14
Yläneenjoki 0.39
− 7
Taipaleenjoki 1
− 6
Lestijoki 0.64
− 3
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
