Methods to Estimate On-Field Nitrogen Emissions from Crop Production as an Input to LCA Studies in the Agricultural Sector

Nitrogen compounds emitted from the field are usually considered in Life Cycle Assessments (LCA) of agricultural products or processes. The environmentally most important of these N emissions are ammonia (NH3), nitrous oxide (N2O) and nitrate (NO3). The emission rates are variable due to the influence of soil type, climatic conditions and agricultural management practices. Due to considerable financial and time efforts, and great variations in the results, actual measurements of emissions are neither practical nor appropriate for LCA purposes. Instead of measurements, structured methods can be used to estimate average emission rates. Another possibility is the use of values derived from the literature which would, however, require considerable effort compared to estimation methods, especially because the values might only be valid for the particular system under investigation. In this paper methods to determine estimates for NH3, N2O and NO3 emissions were selected from a literature review. Different procedures were chosen to estimate NH3 emissions from organic (HORLACHER & MARSCHNER, 1990) and mineral fertilizers (ECETOC, 1994). To calculate the N2O emissions, a function derived by Bouwman (1995) was selected. A method developed by the German Soil Science Association (DBG, 1992) was adopted to determine potential NO3 emissions. None of the methods are computer-based and consequently require only a minimum set of input data. This makes them, on the one hand, transparent and easy to perform, while, on the other hand, they certainly simplify the complex processes.