Legumes

legumes

Photo: Shannon McGee on Flickr, shared under CC-BY-SA licence

Photo: Shannon McGee on Flickr, shared under CC-BY-SA licence

A legume is a plant from the Fabaceae (pea or bean) family. Most of them have the amazing ability to fix (or change) atmospheric nitrogen into readily available nitrogen in the soil, i.e. nitrogen that other plants and organisms can use. They do this by having a special relationship with the nitrogen fixing bacteria, Rhizobium, which lives inside their root nodules. This makes them perfect for use in intercropping, crop rotations, and as cover crops.  Note that the legume plant should be left in the soil to die down at the end of its growing season so that the nitrogen it has fixed can be returned to the soil.

Key benefits:

  • Increase the quantity of readily available nitrogen in the soil, decreasing the need for artificial nitrogen fertilisers
  • Increase the yield of the subsequent crop/ crops grown alongside legumes
  • Often an edible, tasty and nutritious source of plant proteins

Disadvantages:

  • Requires upkeep. They struggle with soil water stress, are sensitive to weed competition, and can be prone to some pests and diseases
  • Some legumes fix less nitrogen than others, e.g. chick peas are not an effective nitrogen fixing legume
  • If grown alongside other crops to provide nitrogen, there may be a trade-off; you may get less of a crop from the legume for more of the second crop
     

Example:

Try including a legume in a crop rotation. For example, broad (or fava) beans are a hardy legume crop that will grow in most climates, with great nitrogen fixing potential. To include these in a crop rotation, simply, plant them where you previously had another crop. For maximum benefit, follow the beans with a crop that requires high nitrogen, then follow that with with a crop that requires little nitrogen, and repeat. Three year cycles help to break the cycle of pests and disease. Choose a well-drained site, and if in sandy soil or low in organic matter, improve with compost

 

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This text is based on an academic literature review by Alice Ambler at the James Hutton Institute as part of our collaborative GROW Observatory project.


 

Flag of EuropeThe GROW Observatory has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 690199.