Legume

Legumes are plants in the pea family, and they also refer to the fruit or seeds of these plants. When the seeds are used as dry grains for food, they are called pulses. People grow legumes mainly for eating, but they are also used for animal feed and to improve soil.

A selection of dried pulses and fresh legumes

One special thing about legumes is that they have a unique kind of fruit that comes from a single part of the flower and usually opens along two sides when it is ready.

Many legumes have tiny bacteria called Rhizobia living in little bumps on their roots called root nodules. These bacteria help the plants get nitrogen from the air, and some of this nitrogen stays in the soil to help future crops grow. Because of this, legumes are very important in crop rotation, which is the way farmers change the types of crops they grow in a field over time.

Terminology

Distribution

Legumes are very common plants. They are the third-largest group of land plants by number of species. Only two other plant groups, the Orchidaceae and Asteraceae, have more species. Legumes include about 751 different groups, called genera, and around 19,000 known species. This makes up about seven percent of all flowering plants.

Ecology

Nitrogen fixation

Main article: Nitrogen fixation

Root nodules on a Wisteria plant (a hazelnut pictured for comparison)

Many legumes have special bacteria called Rhizobia living in small bumps on their roots, called root nodules. These bacteria can take nitrogen from the air and change it into a form that plants can use. This helps legumes grow well because they get the nitrogen they need to make proteins.

When legume plants die and stay in the field, the nitrogen they stored is released back into the soil. This makes the soil richer and helps future plants grow better. Farmers often grow legumes together with other plants to keep the soil healthy without using extra fertilizers.

Pests and diseases

Legumes play a key role in the nitrogen cycle, making nitrates available to other plants in the soil.

Some small flies called "bean flies" can damage legume crops, especially in warm parts of the world. They can destroy young plants. Other pests like black bean aphids, pea weevil, and bean weevil also harm legumes by eating leaves and other parts of the plant.

Legumes can also get sick with different diseases. Some of these are caused by tiny living things, like fungi and bacteria, while others are caused by things in the soil or bad growing conditions. These problems can make it hard for the plants to grow well.

Storage

Keeping legume seeds for a long time can make them harder to grow. Studies with vetch, broad beans, and peas show that these seeds stay good for about 5 years when stored properly. The best way to keep seeds healthy is to control the air and temperature around them. Lower temperatures help seeds last longer, and cooler air helps keep the seeds drier.

Uses

Legumes are plants grown for many different purposes, such as food, animal feed, and improving soil. They can be used in many ways depending on when they are harvested.

Grain legumes, like beans, lentils, lupins, peas, and peanuts, are grown for their seeds. These seeds are eaten by people and animals or used to make oils. Legumes are also used to make plant-based foods that taste like meat or dairy.

Legumes are also grown to feed animals. Some, like alfalfa and clover, are eaten directly by animals. Others are cut and given to animals as food. These plants help animals grow better than just eating grass.

Other uses for legumes include growing them for their pretty flowers, like lupins, or for making natural dyes and gums. Some legumes are planted to help the soil by adding nutrients. Others are grown for timber, and some legume trees can be used in farming systems that mix trees and crops together.

History

Neanderthals and early modern humans used wild pulses in their meals as long as 70,000 to 40,000 years ago. Traces of pulse farming have been found near the Ravi River in Punjab, an important area of the Indus Valley civilisation, dating back to around 3300 BC. Evidence of lentil growing has also been found in Egyptian pyramids and old cuneiform recipes. Dry pea seeds from a village in Switzerland are thought to be from the Stone Age. These peas were likely grown in the eastern Mediterranean and Mesopotamian areas at least 5,000 years ago, and in Britain as early as the 11th century. The soybean was first grown about 5,000 years ago in China from a wild vine called Glycine soja.

The oldest known domesticated beans in the Americas were found in Guitarrero Cave in Peru, dating to around the second millennium BCE. Studies of the common bean Phaseolus show it began in Mesoamerica and then spread south along with maize and squash, which are often grown together. In the United States, the soybean was brought in 1770 by Benjamin Franklin, who sent seeds to Philadelphia from France.

Pulses for sale in a Darjeeling market

International Year of Pulses

Main article: International Year of Pulses

The International Year of Pulses in 2016 was announced by the Sixty-eighth session of the United Nations General Assembly. The Food and Agriculture Organization of the United Nations helped organize activities with governments and other groups. The goal was to teach people more about how pulses can provide good nutrition, support sustainable food production, help achieve food security, and improve nutrition. This year aimed to encourage better use of pulse proteins, increase pulse farming, improve crop rotations, and solve problems in worldwide pulse trade.