Environmental impact assessment of agricultural production systems using the life cycle assessment (LCA) methodology II. The application to N fertilizer use in winter wheat production systems

Abstract

This study examined the environmental impact of different nitrogen (N) fertilizer rates in winter wheat production by using a new life cycle assessment (LCA) method, which was specifically tailored to crop production. The wheat production system studied was designed according to “good agricultural practice”. Information on crop yield response to different N rates was taken from a long-term field trial in the UK (Broadbalk Experiment, Rothamsted). The analysis considered the entire system, which was required to produce 1 ton of wheat grain. It included the extraction of raw materials (e.g. fossil fuels, minerals), the production and transportation of farming inputs (e.g. fertilizers) and all agricultural operations in the field (e.g. tillage, harvest). In a first step, all emissions and the consumption of resources connected to the different processes were listed in a Life Cycle Inventory (LCI) and related to a common unit, which is 1 ton of grain. Next a Life Cycle Impact Assessment (LCIA) was done, in which the inventory data are aggregated into indicators for environmental effects, which included resource depletion, land use, climate change, toxicity, acidification, and eutrophication. After normalization and weighting of the indicator values it was possible to calculate summarizing indicators for resource depletion and environmental impacts (EcoX). At N rates of 48, 96, 144 or 192 kg N/ha the environmental indicator “EcoX” showed similar values per ton of grain (0.16–0.22 EcoX/ton of grain). At N rates of zero, 240 and 288 kg N/ha the EcoX values were 100–232% higher compared with the lowest figure at an N rate of 96 kg N/ha. At very low N rates, ‘land use’ was the key- environmental-factor, whereas at high N rates ‘eutrophication’ was the major problem. The results revealed that agronomical optimal arable farming does not necessarily come into conflict with economic and environmental boundary conditions.