Legume-based crop rotations as a strategy to mitigate fluctuations in fertilizer prices? A case study on bread wheat genotypes in northern Spain using life cycle and economic assessment

Today's agricultural production is heavily dependent on synthetic nitrogen (N) fertilizer. Its energy-intensive production and use are associated with a number of environmental burdens, such as global warming and marine eutrophication. Furthermore, fertilizer prices are subject to high volatility and have been rising steadily for years. One strategy to reduce the dependence on synthetic N fertilizer is to include legumes in the crop rotation, but it is important that this practice is economically viable to be adopted by farmers. Through gross margin analysis and life cycle assessment (LCA), we quantified the economic and environmental impacts of introducing grain legumes into rainfed bread wheat rotations in northern Spain. The analysis covered the full two-year sequences of barley-wheat, rapeseed-wheat and vetch-wheat. We further investigated the effect of four different bread wheat genotypes on the environmental and economic performance. In this case study, replacing synthetic N fertilizer with legume-fixed N in a two-year cropping rotation decreased most of the analysed environmental impacts. Modelled greenhouse gas emissions were 24 % lower for vetch-wheat compared to barley-wheat and 11 % lower compared to rapeseed-wheat. Despite higher wheat yield, the vetch-wheat rotation had an 18 % lower gross margin than the rapeseed rotation and a 1 % higher gross margin than the barley rotation. The sensitivity analysis showed that only when fertilizer and wheat grain prices were more than doubled, that the legume rotation became more profitable than the other rotations. Consequently, farmers would require a financial incentive to include legumes in crop rotations and reduce environmental impacts.