Keywords: Life cycle assessment, nitrogen, minfertilisers, energy balance, greenhouse gas emission, N2O, carbon footprint.
The ‘environmental footprint’ of crop production in general and of fertiliser use in particular includes a wide range of different impacts like nitrate leaching, ammonia volatilisation, greenhouse gas emissions or energy consumption, which itself may contribute to different environmental effects e.g. eutrophication, acidification, and global warming.
The life-cycle assessment (LCA) methodology is particularly suitable to examine and analyse the ‘environmental footprint’, since LCA is an inventory and evaluation of all environmental impacts (emissions and resource consumption) along the ‘life-cycle’ of a product from ‘cradle to grave’. For fertiliser this means the inclusion of raw material extraction, through production to application. Today, LCA is a standardised methodology (ISO 14040 series) and the EU promotes ‘Life Cycle Thinking’ through public inventory data (ELCD database) and LCA related information and recommendation (ILCD Handbook). LCA is mainly used to compare different alternatives (products or services) and to determine their environmental ‘hot-spots’.
The LCA approach can be used in different ways. Its first application was on energy balances, where the energy consumption and energy production is evaluated. The energy balance of crop production is generally very positive, because agricultural crops fix several times more solar energy in their biomass than what is consumed during their cultivation in terms of fertiliser, fuel etc.
A complete LCA study aims at including all potential environmental impacts, which are for crop production systems eutrophication, off-site acidification, global warming, toxicity, and resource consumption (land, water, minerals, fossil fuels). The paper gives examples of wheat production at different nitrogen application rates and with different nitrogen fertiliser types.
Today, the LCA approach is often applied in order to determine the so-called ‘carbon footprint’ of products or production systems. Carbon footprint studies of crop production are particularly critical, because it is not only the energy-related CO2 emissions that are relevant, but in addition there are other specific issues to be considered. These are for instance (1) direct and indirect nitrous oxide (N2O) emissions, (2) potential land-use change impacts (e.g. CO2 from deforestation), (3) varying greenhouse gas emissions from different fertilisers and fertiliser production technologies, and finally, the CO2 fixation in crops, which is only accountable if fossil fuels are replaced by bio-energy sources. This paper gives examples of carbon footprint calculations of winter wheat produced in Europe.
It can be concluded that LCA has become the standard methodology for environmental analyses. LCA can also be applied to agricultural production systems, but the close interaction with natural resources such as land, soil, water and nutrients requires special consideration. In particular for land use and land use change impacts the methodologies are currently under discussion and development (e.g. for proper bio-energy assessments).
LCA studies have shown that agricultural crops grown at optimum intensity have a lower environmental footprint per product unit than low-input systems mainly because they utilise the available resources (e.g. land) more efficiently and thereby can support the preservation of natural ecosystems with high carbon sequestration potential. Improved fertiliser production technology and best agricultural management practices with high nitrogen use efficiency allow a further significant reduction of the environmental impact of crop production.
F Brentrup and J Lammel, Yara International, Research Centre Hanninghof, Germany.
20 pages, 12 figures, 1 table, 31 references.