Ecological services of faba bean

Ulrich Köpkea¹ and Thomas Nemecekb²

Abstract
The key environmental benefits of faba bean are its ability to fix atmospheric nitrogen symbiotically under a broad spectrum of environmental conditions and making this renewable resource available to show positive precrop effects in diversified crop rotations. Non-nitrogen precrop effects entail potential benefits via increased availability of soil phosphorus to the subsequent crops. Faba bean acts as a break crop in intensive cereal-dominated crop rotations.

Faba bean enables diversification of the agroecosystem, i.e. planned biodiversity in time via diversified crop rotations and in space via intercrops, indirectly enhancing associated diversity of wild flora, wild fauna and soil microbes that may affect the sustainability of agricultural systems. Nevertheless, most effects are indirect effects on soil fertility, productivity, and system stability, as well as resilience of the entire agroecosystems, effects that can seldom be attributed solely to this crop.

The environmental impacts of grain legumes have been studied at different levels by means of life cycle assessment (LCA). Considering the individual crops, it can be shown that faba bean enables savings of energy and reductions of greenhouse gas emissions, but it is difficult to assess all precrop effects at the individual crop level. First, comparisons of whole crop rotations with and without grain legumes show reductions of energy consumption, global warming, ozone formation, and acidification and ecotoxicity in intensive cereal-rich crop rotations. Eutrophication was at a similar level, with a tendency for increased nitrate leaching and a decrease of other N emissions. Replacement of imported soybean meal by locally produced pulses could have a favourable effect, particularly for pulses produced and used on-farm. However, depending on the raw materials used to replace soybean meal, the effects can also be unfavourable. Finally, shifting the human diet toward less reliance on meat has the potential to reduce environmental burdens, but care must be taken that the plant products are not too highly processed.


Source
Field Crops Research (2010) 115: 217-233


Author Locations and Affiliations
(1) IOL – Institute of Organic Agriculture, University of Bonn, Katzenburgweg 3, D-53115 Bonn, Germany
(2) Agroscope Reckenholz-Tänikon Research Station ART, Reckenholzstrasse 191, CH-8046 Zurich, Switzerland


Posted February 2010