This article looks at the agronomic advantages of legume crops, particularly for organic farming, and reports on recent findings regarding their nutritional benefits.
Beans, lentils, peas, and chickpeas are all used as food, while animal feed makes use of other legume crops that have either protein-rich seeds – protein crops known as pulses – such as peas, broad beans, soybean, and lupin, or are used as fodder, such as alfalfa and clover.
The distinguishing feature of legume crops, found nowhere else in the plant kingdom, is their ability to fix nitrogen from the air. This confers them with an agronomic advantage that is particularly important when it comes to organic agriculture; they reduce the use of nitrogen fertiliser, while also reducing the need for fossil fuels to produce, transport, and apply nitrogen fertiliser. Legume crops also contribute to lower greenhouse gas emissions because nitrogen fertilisers are the source of atmospheric nitrous oxide (N2O), a gas whose impact to climate change is 300 times greater than carbon dioxide.
Another benefit of legume crops is their contribution to diversifying crop rotations, which have become quite short and based on a small number of species. Using legume crops reduces the growth of weeds, disrupts parasite lifecycles, and can reduce the use of pesticides.
In addition, pulses such as peas, broad beans, and lupins, constitute a particularly important source of plant protein in animal feed.
Despite these numerous benefits, the production of legume crops has continued to fall in France and in Europe since the 1980s for a number of reasons, including the low cost of nitrogen fertiliser and the higher levels of economic support given to grain crops. Protein crop production in Europe is insufficient and 75% of the plant protein used in animal feed in Europe must be imported, primarily in the form of soycakes.
Rekindling interest in legume crops has become an important issue in organic farming. To do so, a better control of plant selection is needed. It will also be necessary to restructure the agribusiness industry, to find new markets, and to develop new harvest and sorting techniques to deal with legume–grain associations – a promising and increasingly-widespread pant combination.
Increasing the share of legumes in field crops was put forward as one of the ten key measures for reducing greenhouse gas emissions in a report prepared by INRA that was commissioned by ADEM, and the French Ministry of Agriculture, Agrifood and Forests, and the Ministry of Ecology, Sustainable Development and Energy. This study, published in July 2013, is entitled How Can French Agriculture Contribute to Reducing Greenhouse Gas Emissions? Abatement Potential and Cost of Ten Technical Measures.