Rhizobia and the Protein Makers

Rhizobia Bacteria: Nature’s Fertilizer Factory

Perhaps the single most applied fertilizer nutrient in all of agriculture is nitrogen.

Nitrogen is exceedingly abundant on our planet via the atmosphere (79% of the air we breathe is nitrogen), but elsewhere on the planet it is hard to find. And for all its abundance in the atmosphere, atmospheric nitrogen is woefully unavailable. Nitrogen in the air is triple-bonded to itself as N2 gas, and that triple bond is monstrous difficult to break apart, which is really unfortunate because that breakage is necessary in order to render nitrogen useable in biological systems.

Nitrogen is difficult to obtain, yet it is a high-demand nutrient. Without nitrogen there would be no amino acids and no proteins – the building blocks of life.

List of Nitrogen Fixing Plants

Legume roots with rhizobia bacteria nodules.

Legume roots with rhizobia bacteria nodules.

Luckily Mother Nature has some troops on hand to tackle this problem – a group of tiny organisms called rhizobia bacteria.

Rhizobia aren’t the only ones responsible for nitrogen fixation, but they do the majority of it by far.

Rhizobia bacteria possess the DNA encoding for a protein called nitrogenase. Nitrogenase is an enzyme that breaks nitrogen gas apart into biologically useable forms. Sounds like a miracle – and it is – but rhizobia do require some help. Triple bonded atmospheric nitrogen, as discussed earlier, is very hard to pull apart. Energetically speaking, it is very expensive for the rhizobia to use nitrogenase. In a way it’s like a big truck: there is a tremendous amount of utility in that size of a vehicle, but the gas bill . . . let’s just say the costs of operation can be steep.

Luckily rhizobia form a wonderful partnership with plants. Plants supply the fuel, in this case carbohydrates that they’ve harvested from carbon dioxide and the sun’s light energy. In return for the carbs, the rhizobia give plants some of the much-needed nitrogen. There is one major catch to this symbiosis…

Rhizobia nodules seen through a microscope.

Rhizobia nodules seen through a microscope.

Only certain plants have the ability to form a relationship with rhizobia.

By and large, this group of plants belong just to the legume botanical family. Beans, peas, peanuts, alfalfa, clover, jicama, and ahipa are good examples of leguminous crops.

Having knowledge of and using leguminous crops is a major plus to anyone interested in producing their own food with greater ease, especially if you want to do it without commercial fertilizers. This is beneficial not only for the soil (commercial fertilizers are technically salts) but also for your wallet.

With the help of rhizobia, legumes self-fertilize; that is, they are able to acquire nitrogen on their own without the need of supplemental fertilizers. Furthermore, legumes add nitrogen to the soil so that other crops can use it.

This can be done by crop rotation where non-leguminous crops are planted in the same spot of ground that leguminous crops were planted in previously, or by intercrop where leguminous crops are planted in and amongst other crops so they will help fertilize them.

You can also add large amounts of legume plant material to a compost pile, thereby enriching it tremendously. Legumes can also help prepare nutrient-poor ground for food production by way of the “chop and drop” method: grow legumes on a patch of ground you want to farm and then cut the legumes back and leave all the trimmings behind on the ground. That way much of the harvested nitrogen stored in the plant tissues gradually decomposes back into the soil and enriches it. With this method, the chopped legume plant itself is quite literally used as a fertilizer. In gardening/agricultural circles this technique is sometimes referred to as green manuring.

Legume trees can also be planted throughout a property and any plant material harvested from those trees (autumn leaves, prunings/trimmings, etc.) can be used as a fertilizer – either on the compost heap or composted in or on the soil.

Did you know leguminous trees are some of the best fuel-producers?

If you heat your house with a wood stove you can grow and cut leguminous trees back for fire wood. Since leguminous trees are self-fertilizing because of their symbiosis with rhizobia they grow back vigorously when cut and can be harvested again for fire wood in the future. This wood-harvesting technique is referred to as coppicing and has been used historically for millennia. By coppicing with leguminous trees, a grower is quite literally growing fuel. I’ve even heard of self-sufficiency gurus who harvest fire wood in this manner to not only heat houses but to fuel steam engines that turn generators and thus power houses or recharge batteries. Pretty cool stuff.

Fuel aside, fast growing legume trees can also be harvested for their timber to make farm structures, fences, furniture, even housing, and so on.

Through the miraculous symbiosis between rhizobia and leguminous plants, nitrogen can be pulled from the atmosphere and put to good use in biological systems. With a sound knowledge of leguminous plants and their potential uses, a grower can wisely use one of nature’s greatest environmentally-enriching phenomena to his/her advantage to grow large volumes of high-quality food and fuel.

List of Nitrogen Fixing Plants

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