Sustainability analysis of irrigated and rainfed wheat production systems under varying levels of nitrogen fertilizer through coupling of emergy accounting and life cycle assessment

Most of the crop production systems have strived for improving crop productivity by increasing various resource inputs; especially water and synthetic nitrogen (N) fertilizer, without considering their environmental consequences. Yet, only few studies have evaluated the sustainability of cropping systems simultaneously using life cycle assessment (LCA) and emergy accounting (EMA) techniques. The former highlights pollutant emissions and environmental impacts, while the latter emphasizes resource consumption and system efficiency. In this threeyear field study, the environmental impacts and sustainability of farming systems were estimated under rainfed and irrigated patterns at four N application rates in the Northwest China. Our result indicated that the irrigated pattern enhanced grain yield by 9%, while simultaneously increasing 8% of environmental impact and 12% of emergy input based on per hectare of wheat production. Almost similar results of environmental impact per kg basis of grain production and emergy sustainability index revealed that irrigation practice did not decrease the overall sustainability of a cropping system. Conversely, the higher N levels of 240 and 360 kg N ha-1 did not provide a proportionate yield return and were accompanied by increased environmental impacts of 20% and 69%, respectively on per kg grain production basis, when compared to an N dose of 120 kg N ha-1. Meanwhile, the gross unit emergy value revealed that the production efficiency under 120 kg N ha-1 was enhanced, in comparison with other N levels. Therefore, a moderate N dose of 120 kg N ha-1 under both irrigated and rainfed patterns is highly recommended for adoption due to its overall advantage in terms of yield returns, environmental impact and production efficiency.