Keywords: energy balance, emission, wheat, life cycle assessment
The paper describes the results of energy balance calculations based on input data from winter wheat field experiments between 1989 and 1997. The nitrogen (N) rates applied varied from 0 to 220 kg N/ha. The N form was calcium ammonium nitrate (CAN). The total energy consumption was calculated for the winter wheat systems including the manufacture of fertilisers, seeds, plant protection substances and machinery, transport from factory to field and all on-farm activities. Energy output in the form of the harvested biomass was calculated using the physical combustion value of the different metabolic components of the grain. A linear relationship was found between increasing energy input into the total system and increasing N fertiliser application. In the absence of N fertilisation, total energy input was 7.5 GJ/ha. This increased to 17.5 GJ/ha, at highest rates of N fertilisation. At each production intensity, defined as N fertilisation level, energy output in the form of grain was much higher than energy input. The energy input to obtain the maximum net energy yield (i.e. energy output minus energy input) was approximately equal to the energy required to achieve economic optimum grain yield.
The consumption of fossil fuels is one environmental aspect of agricultural production. Another aspect is the release of different emissions to soil, air and water. Consequently, the environmental impact of fertiliser production, transport and use has to be seen in a Life Cycle perspective to get a right ranking of all environmental impacts. Therefore a Life Cycle Assessment (LCA) was carried out to examine the impacts of using different types of fertilisers (solids, liquids and manure) in winter wheat production.
Different LCA procedures are used to assess the environmental impacts (e.g. global warming, eutrophication, acidification, depletion of fossil fuels) of the wheat production systems, taking account of the potential of each impact to harm the environment. The results show reasonable differences dependent on the methodology used.
JÃƒÂ¼rgen KÃƒÂ¼sters, Centre for Plant Nutrition and Environmental Research Hanninghof, Hydro Agri, Germany
27 pages, 10 tables, 14 figures, 24 refs.