Environmental effects of energy crop cultivation in Sweden—I: Identification and quantification
Introduction
Replacing fossil fuels with biomass leads to global environmental benefits such as reduced emissions of greenhouse gases. However, not only the use of biomass could lead to benefits for the environment, but also the production of the biomass. This paper will show that when traditional annual food crops are replaced by dedicated perennial energy crops on Swedish arable land, negative environmental effects from current agriculture practices such as erosion, nutrient leaching and the emission of greenhouse gases, may be reduced. Similar conclusions have been drawn in earlier studies concerning, for example, perennial energy crop production in the USA (see e.g., Tolbert[1]; McLaughlin and Walsh[2]; Kort et al.[3]; Grigal and Berguson[4]; Bransby et al.[5]). Energy crop systems can also be used to purify municipal waste, thus reducing negative impacts from the community. Furthermore, the content of heavy metals in the soil could be reduced through cultivation of short-rotation forest. These environmental benefits could increase the value of the energy crops, thereby affecting future market conditions for biomass.
In this paper, environmental changes are identified and quantified when traditional food and forage crops produced with current agriculture practices are replaced by perennial energy crops on Swedish arable land. This paper, which is based mainly on a literature review, represents Part I of the analysis, which is complemented by a second part in which an economic valuation of the environmental changes is carried out (see Börjesson[6]). Thus, this paper is a background to the second paper, which includes a more integrating synthesis. The purpose with the overall study is to analyse how energy crop cultivations in Sweden could be located and managed to maximise environmental benefits. Neither environmental effects arising from replacing fossil fuels by biomass nor environmental benefits from the reduced use of fossil fuels in perennial energy crop cultivation, in comparison to annual crop cultivation, are included in this study as such benefits have already been analysed in earlier studies (see e.g., Börjesson7, 8). The magnitude of the environmental benefits depends on, for example, geological and geographical conditions, while population density influences the amount of municipal waste that can be recycled on energy crop cultivations. Thus, the environmental impact is analysed on a regional basis and then aggregated to a national level. Since agricultural practices, the load of antrophogenic pollutants and the generation of waste, are changing over time, the potential impact of energy crop cultivation also changes over time. The time during which environmental advantages could be achieved is therefore estimated.
Section snippets
Methodology and assumptions
Energy crops included in this analysis are short-rotation forest (Salix) and energy grass (reed canary grass). In the north of Sweden, only reed canary grass is assumed to be grown for energy purposes as the climatic conditions are not suitable for Salix cultivation[9]. This situation can, however, change in the future if more frost resistance Salix clones will be available. The energy crop cultivations are assumed to be geographical equally distributed on current arable land used for perennial
Greenhouse gases
Greenhouse gas emissions from arable land can be reduced in three different ways when annual crops are replaced by perennial energy crops, through (i) accumulation of soil carbon (C) in mineral soils, (ii) reduced carbon dioxide (CO2) emissions from organic soils, and (iii) reduced nitrous oxide (N2O) emission caused by the use of fertilisers. Changes in the emissions of other greenhouse gases are estimated to be small and are therefore neglected.
Conclusions and discussion
An overall conclusion of this study is that the environmental benefits from large-scale introduction of energy crop production in Sweden could be substantial, as the negative environmental impact from current agriculture practices and municipal waste treatment could be significantly reduced. The carbon dioxide emission from organic soils through biological oxidation of the organic matter, for example, could be significantly reduced (by about 7 tonne C/ha yr) when annual crops are replaced by
Acknowledgements
I would like to thank L. Gustavsson, B. Johansson and A. Lundborg for reviews and useful comments. I also gratefully acknowledge the economic support provided by Vattenfall AB and The Swedish National Board for Industrial and Technical Development.
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