Thursday, March 11, 2010

The Nitrogen Fixers

In high school, a classmate asked my chemistry teacher if nitrogen gas was poisonous. She took a deep breath, held it a second, and let it out, only then saying simply “no.” Her point is well taken. We live our lives awash in a sea of nitrogen gas. It makes up 80% of every breath you take. Yet this vital element is largely unobtainable to most life. Plants need nitrogen to make green leaves. We need it as it is a vital part of many nutrients, most notably protein. So how does it get converted to a usable form? Well, lightning helps a bit. However, most of the real work is done by bacteria. Some of these bacteria live in the soil, producing tiny amounts of biologically available nitrogen as they need it. But the real workhorses get a little help. You see, legumes have formed a symbiotic relationship with nitrogen-fixing bacteria. The legumes form nodules on their roots that create an ideal habitat for the bacteria, which usually lives in the soil, to move in, multiply, and start fixing large amounts of nitrogen.

So, what are these mysterious legumes, how do you get them, and do you really need them? First of all, yes you need them. It really is one of the best ways to get lots of nitrogen in your soil without resorting to buying large bags of fertilizer. Many food crops, such as corn and squash are heavy feeders and steal large amounts of nitrogen from your soil. Legumes form a vital step in crop rotation, replenishing the nitrogen content of the soil.

So what are legumes? Legumes are a family of plants that include peas, beans, peanuts, clover, alfalfa, and hairy vetch, among many, many others. Clover and vetch make great green manures, alfalfa makes great feed for livestock and, of course, peas, peanuts and beans make food for us. I’ll cover green manure in a future post.

There is one important thing to remember, though. Each species of legume forms a symbiotic relationship with one specific species of bacteria. If you have ever grown that kind of legume in that soil, the bacteria is present in the soil. If not, you should spend a few dollars and inoculate the soil.

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