Legumes, members of the family Fabaceae, are important components of TLI’s vision of a Natural Systems Agriculture. Their symbiosis with root-nodule bacteria (rhizobia) enables them to supply more than 100 Tg of biologically-available nitrogen to natural and agroecosystems each year through biological nitrogen fixation (BNF). This process, BNF, has been called the most fundamental biological process on earth aside from photosynthesis because nitrogen is the critical limiting element for plant growth. Availability of sufficient nitrogen to crop plants is essential for producing high-quality, protein rich, plant-based foods, and the entire nutritional nitrogen requirement for humans is obtained directly or indirectly from plants.
During plant domestication, legume crops were developed to maintain or increase soil fertility through nitrogen additions for subsequent crop species (like cereal grains) while simultaneous providing high protein seeds for human consumption or highly nutritious forage for livestock. Legumes continue to supply approximately 13% of the annual global agricultural nitrogen requirements, with synthetic inorganic nitrogen fertilizers fulfilling the vast majority of the remaining nitrogen requirements. Increasing the use of legumes for BNF is close to the idea of ecological intensification, using ecological processes rather than external inputs for crop production.
Despite all their benefits, just over a dozen grain legumes (annuals) and a few dozen forage legumes (annuals and perennials) are globally traded and commercially important. With more than 19,500 species in the legume family, humans have probably overlooked many species that merit further investigation and possibly domestication as new crop plants.
We are working closely with the Perennial Agriculture Project Global Inventory (PAPGI) team to identify promising perennial legume species and to develop criteria for evaluating their agronomic potential as perennial crop plants using the pipeline strategy for domestication as a guide.
Perennial Grain Legumes
Perennial grain legumes, though currently non-existent, would be uniquely situated as crop plants able to provide relief from reliance on synthetic nitrogen while supplying stable yields of highly nutritious seeds in low-input agricultural systems. We are currently evaluating some native perennials such as lupins and some non-natives (alfalfa, sainfoin, etc.) as possible new grain legumes.
Companion Grain Legumes
We are also exploring various temperate-adapted wild and cultivated forage legumes as continuous living cover companion species (intercrops) with other TLI perennial grains. We are particularly interested in alfalfa, Kura Clover, and some Astragalus species that fit our criteria for perennial legumes that facilitate BNF and nitrogen-transfer in perennial polyculture cropping systems.
 Erik Steen Jensen and others, ‘Legumes for Mitigation of Climate Change and the Provision of Feedstock for Biofuels and Biorefineries. A Review’, Agronomy for Sustainable Development, 32.2 (2012), 329–64 <https://doi.org/10.1007/s13593-011-0056-7>.
 Jagdish K. Ladha and others, ‘Efficiency of Fertilizer Nitrogen in Cereal Production: Retrospects and Prospects’, Advances in Agronomy, 87.5 (2005), 85–156 <https://doi.org/10.1016/S0065-2113(05)87003-8>; T. E. Crews and M. B. Peoples, ‘Legume versus Fertilizer Sources of Nitrogen: Ecological Tradeoffs and Human Needs’, Agriculture, Ecosystems and Environment, 102.3 (2004), 279–97 <https://doi.org/10.1016/j.agee.2003.09.018>.
 J.N. Galloway and others, ‘Nitrogen Cycles: Past, Present, and Future’, Biogeochemistry, 70.2 (2004), 153–226 <https://doi.org/10.1007/s10533-004-0370-0>.
Brandon speaks about work on perennial legumes at the 2018 Prairie Festival.
Related Scientific Publications
Learn about other perennial crops under development at The Land Institute.