Agriculture, Ecosystems and Environment 80 2000 277–290
Leaching of nitrogen in Swedish agriculture — a historical perspective
M. Hoffmann
a,∗
, H. Johnsson
a
, A. Gustafson
a
, A. Grimvall
b
a
Department of Soil Sciences, Division of Water Quality Management, Swedish University of Agricultural Sciences, P.O. Box 7072, SE-750 07 Uppsala, Sweden
b
Department of Mathematics, Division of Statistics, Linköping University, SE-581 83 Linköping, Sweden Received 26 April 1999; received in revised form 5 January 2000; accepted 15 March 2000
Abstract
There is a need to examine long-term changes in nitrogen leaching from arable soils. The purpose of this study was to analyse variations in specific leaching rates kg ha
− 1
per year and gross load Mg per year of N from arable land to watercourses in Sweden from a historical perspective. The start of the study was set to 1865 because information on crop distribution,
yield and livestock has been compiled yearly since then. The SOILSOILN model was used to calculate nitrogen leaching. Calculations were done for cereals, grass and bare fallow for three different soil types in nine agricultural regions covering a
range of climatic conditions. Results indicate that both specific leaching rates and gross load of nitrogen in the middle of 19th century were approximately the same as they are today for the whole of south and central Sweden. Three main explanations
for this were 1 large areas of bare fallow typical for the farming practice at the time; 2 enhanced mineralisation from newly cultivated land; and 3 low yield . From 1865, i.e. the start of the calculations, N leaching rates decreased and were at their
lowest around 1930. During the same period, gross load was also at its lowest despite the fact that the acreage of arable land was at its most extensive. After 1930, average leaching increased by 60 and gross load by 30, both reaching a peak in
the mid-1970s to be followed by a declining trend. The greatest increase in leaching was in regions where the increase in animal density was largest and these regions were also those where the natural conditions for leaching such as mild winters
and coarse-textured soils were found. Extensive draining projects occurred during the period of investigation, in particular an intensive exploitation of lakes and wetlands. This caused a substantial drop in nitrogen retention and the probable increase
in net load to the sea might thus have been more affected by this decrease in retention than the actual increase in gross load. © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Agricultural land; Gross load; Long-term modeling; Nitrogen leaching; Sweden
1. Introduction
Modern agriculture is normally supported by a high input of N fertilisers, and numerous studies have
demonstrated that losses of N from arable land to
∗
Corresponding author. Tel.: +46-8-787-54-44; fax: +46-8-24-81-19.
E-mail address: markus.hoffmanlrf.se M. Hoffmann
water can be substantial. In Sweden, average leaching root zone of N is estimated to be 22 kg N ha
− 1
per year Johnsson and Hoffmann, 1998. Long-term average
measured N concentration in drainage waters varies from 4 to 23 mg l
− 1
Johansson et al., 1999. Nitrate concentration in groundwater is less of a concern in
Sweden compared to many other countries because of low population density, and because about half the
drinking water is supplied from surface waters such
0167-880900 – see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 8 8 0 9 0 0 0 0 1 5 4 - 7
278 M. Hoffmann et al. Agriculture, Ecosystems and Environment 80 2000 277–290
as lakes, where nitrate concentrations generally are low. However, locally in agricultural areas in southern
Sweden, nitrate in groundwater is a concern and it is estimated that about 100 000 people have private
wells with nitrate concentrations well above 50 mg l
− 1
Thoms and Joelsson, 1982. For these reasons, the fo- cus in Sweden is mostly on agricultural N load to the
Baltic Sea instead of nitrate pollution of groundwater. Water quality data from major European rivers, such
as the Rhine and the Daugava, indicate that a major increase in riverine loads of N coincided with the in-
creased use of commercial fertilisers during the first decades of the post-war period Tsirkunov et al., 1992;
Grimvall et al., 2000. However, the relationship be- tween N input to agriculture and export of N from
land to sea is complex. Firstly, the turnover of N in soil involves a variety of different processes operating
on a wide range of time-scales. Secondly, long-term changes in riverine loads of N may, at least in part,
be due to drainage of agricultural land, ditching of wetlands and other measures that influence the reten-
tion of N during transport from field to river mouth. Thirdly, the classic experiments at Rothamsted indi-
cate that, due to a less efficient N uptake in crops, losses of this element from arable land to water were
already considerable in the 19th century Lawes et al., 1881. Another reason for taking a historic view of N
leaching from arable land is that most of the arable land in Sweden is situated within the catchment of
the Baltic Sea. The Baltic is often considered to have been in a more healthy condition in the first half of the
20th century. Since agriculture today is considered to be the largest single source of N outlet to the Baltic
Sea, it is important to study change in N load from agriculture over a longer time perspective. This will
increase overall understanding of the causes of dete- riorating water quality in the Baltic Sea.
Hence, there is a great need for a closer examination of long-term changes in the leaching of N from arable
soils. No systematic study of this has previously been done for Swedish conditions.
Only a few monitoring data are available before the 1970s. Sondén 1912 was one of the first researchers
in Sweden to compile water quality analyses for a large number of lakes and rivers, but without pointing
out any particular source such as agriculture. Arrhe- nius 1954 investigated nitrate concentrations in dug
wells and suggested that there was an influence of nitrate originating from arable land. One of the first
measurements of nitrate leaching from arable land was conducted in 19491950 by Wiklander and Wall-
gren 1960, who estimated nitrate leaching of 4 kg NO
3
–N ha
− 1
with 123 mm discharge on a clay soil in central Sweden. Wiklander and Wallgren 1970
collected 358 samples of drainage water throughout Sweden in 1965 and concluded from their own cal-
culations that minimum and maximum N leaching varied between 4 and 8 kg ha
− 1
on average for the whole country, and between 8 and 17 kg ha
− 1
in the county of Skåne, south of Sweden. From these few
and scattered measurements, it is difficult to draw any conclusions concerning N leaching in the past.
The current systematic monitoring programmes were started at the beginning of the 1970s.
For the purpose of this study, past N leaching was estimated by combining agricultural statistics with a
process-oriented model of the turnover of N in arable soils. An internationally unique collection of agricul-
tural statistics, going as far back as 1865, makes Swe- den an excellent case for such a study. Data regarding
land use, fertiliser application, livestock density, crop distribution and crop yields were used as model inputs
together with soil characteristics and climate data. N losses from the root zone of arable land were then es-
timated using the SOILSOILN model Jansson and Halldin, 1979; Johnsson et al., 1987 of the vertical
transport of water and N through profiles of arable soils.
2. Materials and methods
