A Plant Part of the Legumes Family That Is Grown for Hay or Forage
The legume is commonly recommended every bit a companion institute. It is believed that the excess nitrogen produced by the legume will aid feed the companion growing adjacent to it. In the Three Sisters agriculture organization the bean provides nitrogen for the corn to abound and since corn needs a lot of nitrogen, it grows better.
Legumes are also an important ingredient in ingather rotation. Abound corn one year and follow that upward with beans or peas the following yr to restore the level of nitrogen in the soil.
There is no doubt that legumes are able to capture atmospheric nitrogen (using bacteria) and convert it to plant usable nitrogen, but how much of this actually benefits other plants? Are legumes a good source of nitrogen for the garden?
Do Legumes Add Nitrogen to the Soil?
Legumes and Nitrification
Legumes, including beans and peas, are able to take a symbiotic human relationship with a specific family unit of leaner chosen rhizobia. The plant roots class nodules (petty bumps), which firm the bacteria. The nodules provide protection for the bacteria and the root provides them with sugars as a food source. In return, the bacteria take atmospheric nitrogen, which plants can't apply, and through a process called nitrogen fixation they catechumen it to ammonia. The ammonia is converted to nitrate as it is captivated by the plant.
Nitrification root nodules on Wisteria roots (hazelnut for scale)
The plant is then able to use the nitrogen to make proteins and other molecules.
This procedure is well understood, and is not up for debate. However, what is much less clear is how does this fixed nitrogen become available to other plants, in what quantities and when?
Note: not all legumes make nodules and some scientists believe not all legumes are able to fix nitrogen. Others believe there is a non-nodulating way for some plants to ready nitrogen.
Most garden writers just presume that a lot of this nitrogen flows to other plants for them to use.
Nitrogen from Live Legumes
Does nitrogen move from a legume establish to a neighbor plant while the legume is even so live? This must be true if the nitrogen is a benefit to a companion plant.
The answer to this question has NOT been fully answered by science. Some research suggests that the nitrogen does movement from one plant to others growing nearby. In ane study wide beans were injected with radioactive urea to meet where it goes. The garlic growing nearby captivated some of the nitrogen from the bean, clearly showing it moved while both plants were alive.
Other research has shown no movement of nitrogen between plants. This motion may depend on environmental weather condition, type of plants, blazon of soil, nutrient levels in soil or other unknown weather.
We don't have a definitive reply, but if nitrogen does move from legumes to other plants, it is about certain that the amount is small because most studies can't find any motility at all.
Legumes keep most of the nitrogen so they tin can use it themselves.
Nitrogen in Living Legumes
Where does a legume shop nitrogen? Some insights into this can be found inDesigning and Maintaining Your Edible Mural Naturally, Robert Kourick, which shows a bean plant and its relative nitrogen levels.
In a green establish before flowering, threescore% of the fixed nitrogen is found above ground in leaves and stem and 40% below footing. The aforementioned plant with mature pods has fourscore% of the plants fixed nitrogen in the seed, nine% in leaves and stem, and rest in the roots.
Are Your Legumes Nodulating?
In social club for legumes to form nodules and host the bacteria, the bacteria needs to exist present in the soil. There are dissimilar species of rhizobia for different types of legumes. If your soil does not comprise the right strain, no nodules volition be formed.
Gardeners solve this problem by inoculating seed with the right leaner at the time of planting. Picayune packs of bacteria can be purchased from seed companies and y'all can also buy seed that is already coated with the right bacteria.
One time the bacteria is in the soil, information technology will survive in that location for several years, so fifty-fifty a 4 twelvemonth crop rotation does not need to be inoculated each fourth dimension.
How do you know if you have the correct leaner in the soil? Abound the legume and have a look at the roots halfway through the summer or in fall. You can easily see the pea-size nodules if they are in that location and they are most visible as the plant blooms.
If the plant did not make nodules you either practise not have the right bacteria in the soil, or you have too much nitrogen. Excess fertilizer volition prevent the formation of the nodules since the plant merely does non need the leaner.
Nitrogen from Dead Legumes
As discussed above, living legumes provide very footling nitrogen to the soil or other plants. Once the legume dies, the nitrogen in the found is returned to the soil, where decomposers (bacteria and fungi) convert the organic affair into free nitrogen ions, like nitrate, which tin can be used by other plants.
This all sounds great, but the story is a bit more complex.
The legume uses near of the nitrogen it obtained to produce seeds – the beans and peas. If you harvest the seeds or whatsoever other function of the plant, you are removing most of the nitrogen before it gets to the soil. In fact, "the residue from a corn crop (a non-legume) contains more than nitrogen than the residual from a bean crop, just because the corn crop has more residue".
Forage crops that are harvested and removed from the land provide well-nigh no nitrogen for future plants because "roots and crowns add little soil nitrogen, compared to the to a higher place basis biomass". About 80% of a plants nitrogen is found above ground.
The other result is one of time. Organic matter takes time to decompose. A rule of thumb is that organic matter decomposes slowly over a 5 year period with some nutrients constantly being released. This is OK for the long term gardener, but if yous remember that legume will provide a lot of nitrogen for next years crop, y'all are incorrect.
There is some shorter term nitrogen released from legumes. As the constitute grows it might shed the nodules as it grows new roots or matures. These discarded nodules are a quicker source of nitrogen for the soil.
Legumes and Companion Planting
Legumes are highly touted equally a great companion constitute because they add nitrogen to the soil for the partner plants. This is simply not true.
They may provide a reasonable amount of nitrogen in futurity years, provided you don't harvest a crop from them, but as a companion plant they fail to meet expectations.
Legumes and Crop Rotation
Legumes tin provide a practiced source of nitrogen in future years provided you don't harvest a crop from them. So a legume cover ingather makes a lot of sense since all of the nitrogen is returned to the soil.
Keep in mind this is a good long term strategy for building up nutrients in soil – not a brusque term strategy.
Clover in Lawns
Clover is a legume and many gardeners suggest growing information technology in a lawn because information technology 'adds nitrogen' for the grass. The idea that clover is synonymous with lots of nitrogen is a myth. Cutting the clover will add together some light-green plant material to the backyard, but the same happens when grass is cutting. Both plants add together some future nitrogen equally the material decomposes in the lawn.
Clover does not add significantly more nitrogen than grass, still, some of that nitrogen did came from the air as fixed nitrogen, whereas all the nitrogen in grass is from the soil. Leaving the clover in a lawn is a good idea, just don't await it to add a lot of nitrogen.
Does the Three Sisters Agriculture Piece of work?
I discussed this in more detail in Three Sisters Agriculture . The part of the story where the bean provides nitrogen for the corn is a myth.
References:
- Image of root nodules; past Rowan Adams
Source: https://www.gardenmyths.com/legumes-add-nitrogen-soil/
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