Optimal environmental design of nitrogen application rate for facultative wheat using life cycle assessment

Abstract

Nitrogen (N) supply is a relevant factor in wheat production, affecting yield and yield components. However, this input plays a dominant role in the environmental impact level arising within all the on-farm growing processes. To assess the effects of N fertilization on environmental impact levels, the agricultural life cycle assessment (LCA) was performed for facultative wheat as affected by sowing date (autumn versus spring) and N fertilization (0, 50, 100, 150, and 200 kg ha−1) on a chernozem soil under Pannonian conditions in Eastern Austria for two years (2019/2020 and 2020/2021). In this study, an LCA was performed to find the optimal cropping design to achieve a low environmental impact with an adequate yield level. Processes from cradle to farm gate were involved within the system boundary. As the functional units, grain N yield and land demand for generating the same grain N yield were used. SimaPro software and the ReCiPe 2016 method with Midpoint and Endpoint characterization model were involved. Data were interpreted for 18 impact categories. From an environmental point of view, wheat crops with high doses of N (˃ 150 kg ha−1) were associated with the highest environmental impact. The appropriate grain N yield should be reached to balance the environmental impact resulting from the fertilizer application and all the other inputs. A sufficient increase in yield must be achieved with increased fertilization to justify additional emissions that are related to N fertilization. Variants of winter wheat with medium inputs of N (between 100 and 150 kg ha−1) were associated with the lowest impact on the environment. Consequently, according to environmental impact assessment, it is disadvantageous not to fertilize wheat with N or, on the contrary, to over-fertilize it with N.