On any given day of the year, you can find legumes growing at Terra Firma. Peas are harvested in the spring. Green beans are a summer and fall crop. We also grow leguminous cover crops — vetch in the winter and cowpeas in the summer — on many of our fields.
The Legume plant family also includes other important agricultural crops such as alfalfa, which is the primary crop grown for hay fed to livestock, clover, soybeans, garbanzos and lentils. There are even leguminous trees.
Legumes have the unique ability to pull nitrogen out of thin air and “fix” it into the soil among their roots, through an ancient relationship that they have developed with a particular type of soil organism. In doing so, they create their own fertilizer. For this reason they are often called “Green Manures”.
This unique biological relationship is also what makes legumes such an important food crop. As most vegans and vegetarians know well, legumes are fairly unique among plants in providing protein. That is thanks to the amino acids that they produce using the nitrogen pulled from the air.
For organic farmers, leguminous crops are an important strategy for building soil. If a legume is grown as a “cover crop” it is not harvested, but rather returned to the soil along with all the nitrogen it has “recycled” from the atmosphere. But even when legumes are harvested for food, they remove little from the soil — essentially giving it a “vacation”.
Most legumes are sprawling, vine-y crops that grow quickly up and out. They shade out weeds and protect the soil from strong winds and heavy rain that might otherwise blow or wash it away. They also produce a large mass of fine roots that further holds the soil in place and leaves it soft and loamy. Crops that are grown afterwards tend to thrive.
Unfortunately for small farms like ours, most legumes (even organic ones) are commodity crops grown on a large scale using highly mechanized systems. That’s good for consumers who rely on them as a cheap and nutritious food source, but it makes it difficult for us to grow them without losing money. So we focus on “vegetable legumes”: beans and peas that are harvested before they mature fully and must be hand-harvested or hand-sorted.
We also grow lots of leguminous cover crops. Technically we don’t “make” any money by growing them, since we don’t harvest anything to sell. But we lose less money by planting them than we would if we grew a crop like pinto beans. And in the long-run, they are key to the financial success of our farm. For example, if we plant a winter cover crop of legumes prior to growing Butternut Squash, the field will yield up to 30% more than if we had not grown the legumes.
Over the long run, we have seen our overall yields increase over time, even if it’s been a year or two since a field was planted in cover crops. As a general rule, we try to put a leguminous cash crop in a field once every four years, and a cover crop in every third year. So on average legumes are growing in all our fields twice over a four-year period.
Legumes are not just a win for farmers and eaters. They provide nectar for bees and other pollinators, as well as habitat for beneficial insects and hunting grounds for hawks, owls, egrets and other birds of prey. Everyone’s a winner.