Agriculture, Ecosystems and Environment 80 2000 1–13
Estimation of the impact of fertilisation rate on nitrate leaching in Finland using a mathematical simulation model
Kirsti Granlund
∗
, Seppo Rekolainen, Juha Grönroos, Antero Nikander, Yki Laine
Finnish Environment Institute, P.O.Box 140, FIN-00251 Helsinki, Finland Received 28 December 1998; received in revised form 24 August 1999; accepted 14 December 1999
Abstract
Agriculture comprises the largest single source of nitrogen N into watercourses in Finland. The emphasis of water protection policy is today on controlling the non-point nutrient losses from agriculture. In this study a mathematical simulation
model was used as a management tool to estimate the changes in nitrate NO
3 −
-N leaching resulting from changes in cultivation practices in Finnish agriculture caused by the Agri-Environmental Support Scheme as a part of the Common
Agricultural Policy of the European Union. Detailed data were collected from about 400 farms by interviewing farmers in four study areas in different parts of the country. The potential impacts of these changes on nitrate losses were then assessed by
a deterministic nitrogen leaching model and regional assessments were made by combining the results of model calculations with digital spatial data about soils, crops and fertilisation, using GIS-software. In general, the use of nitrogen fertilisers
inorganic fertilisers and manure has decreased to meet the requirements of the Support Scheme. However, the estimated potential impacts on nitrate losses were rather small 3–14 in different study areas. The model results showed that to
achieve the targeted national and international reductions in agricultural nitrate leaching, fertilisation and particularly manure spreading should be reduced and adjusted better to the actual nitrogen requirements of crops. © 2000 Elsevier Science B.V.
All rights reserved.
Keywords: Agriculture; Nitrogen; Fertilisation; Manure; Modelling
1. Introduction
In Finland, modern intensive and concentrated agri- culture comprises the largest single nitrogen source to
surface waters. Today, the estimated total nitrogen load from agricultural land in Finland is 20 000–40 000 Mg
per year, and the phosphorus load is 2000–4000 Mg per year. Due to several mild and rainy winters in the
late 1980s and early 1990s, the nitrogen load increased
∗
Corresponding author. Tel.: +358-9-40300243; fax: +358-9-40300290.
E-mail address: kirsti.granlundvyh.fi K. Granlund
distinctly in southern Finland Kallio, 1995; Reko- lainen et al., 1995. A model-based regional analysis
of erosion and nitrate losses from agricultural land in the Nordic countries Rekolainen and Leek, 1996
showed that in Finland the risk of nitrate leaching was somewhat higher than in Sweden but consider-
ably lower than in Denmark and some parts of Nor- way. The analysis reflected the different agricultural
practices in the Nordic countries, especially the fer- tilisation rates, and differences in climatic conditions.
In Finland, nutrient loads have caused eutrophication of surface waters, and contamination of groundwaters
by nitrates has been detected in areas where cultivated
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 3 2 - 8
2 K. Granlund et al. Agriculture, Ecosystems and Environment 80 2000 1–13
fields or intensive livestock production and fur farms are located adjacent to groundwater formation areas.
Dissolved reactive
phosphorus, being
totally bioavailable, has been considered to be of crucial im-
portance in controlling the eutrophication of surface waters in Finland. In recent years, however, the role
of nitrogen as a limiting factor in primary production in lakes and rivers has become more clear. Pietiläi-
nen 1997 carried out a comprehensive survey of nutrient status in Finnish lakes and rivers, based on
the ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus. The results showed that 27
of the lakes and 25 of the rivers were nitrogen lim- ited. Furthermore, nitrogen is the limiting factor for
algal growth in the Baltic Sea during the major part of the year Granéli et al., 1990; Kivi et al., 1993. As
Finnish agriculture is concentrated in coastal areas or in river valleys discharging to the Baltic Sea, the need
to reduce nitrogen losses is greatest in these areas Valpasvuo-Jaatinen et al., 1997.
According to a Decision-in-Principle by the Finnish government in 1998 Ministry of the Environment,
1998, nitrogen loading from agriculture should be re- duced by 50 from the level in the beginning of the
1990s by 2005. Additionally, international agreements within the HELCOM framework aim at similar reduc-
tions in nitrogen loads to the Baltic Sea HELCOM, 1994.
In order to reduce the agricultural nutrient losses, the Finnish Agri-Environmental Support Scheme
was implemented when Finland joined the European Union in 1995, in keeping with Common Agriculture
Policy EEC, 1992. The goal of the Scheme is to en- sure the development of agricultural practices towards
higher sustainability. In a priori assessments it has been estimated that a 25–40 reduction in nutrient
losses may be achieved by full implementation of the Scheme Valpasvuo-Jaatinen et al., 1997. Accord-
ing to this programme farmers are paid for adopting environmentally sound management practices. A de-
tailed description of the programme was presented by Valpasvuo-Jaatinen et al. 1997. In 1998, more
than 90 of Finnish farmers participated in the pro- gramme. During the first 3 years 1995–1997 of the
programme, its implementation and changes in agri- cultural practices have been monitored by interview-
ing farmers in four study areas in Finland Grönroos et al., 1998.
A monitoring network of water quality is needed to evaluate the actual impacts of altered practices. How-
ever, due to slow responses of water quality to changes in practices and high fluctuations in annual nutrient
losses caused by meteorological variation, monitoring programmes cannot detect changes occurring within
short time periods. The objective of this study was to assess the potential impacts of changes in cultivation
practices on nitrate leaching in the study areas by using a mathematical simulation model. The SOIL-N
nitrogen model Johnsson et al., 1987 was used as a tool to estimate the potential changes in nitrate losses
on the basis of information about crops, soils, fertilisa- tion rates and management practices. This paper gives
an overview of the regional changes in nitrogen fer- tilisation rate resulting from the Agri-Environmental
Support Scheme and presents the calculated potential changes in nitrate leaching caused by changes in
fertilisation rate.
2. Materials and methods
