Do any plants add nutrients back into the soil as they grow?

Question

It seems reasonable that there ought to be at least a few symbiotic plant varieties that benefit from improving soil condition for other plants.

If not that, are there plants that essentially improve soil conditions if not by improving land fertility?

Improve may be relative as certain plants do have different requirements so I am imagining a sort of 'balancing' plant.

Maybe the answer is something like 'most non-fruiting plants' but I'd think most of those still are about getting what they need and not improving it for others.

For the sake of argument, say you have a near-barren lawn that only has little bits of scattered grasses. Aside from manually adding the fertile soil, can plant-life improve it?

Answer 1

Legumes are often used for this purpose. From Wikipedia:

Legumes are notable in that most of them have symbiotic nitrogen-fixing bacteria in structures called root nodules.

And

Within legume nodules, nitrogen gas from the atmosphere is converted into ammonia, which is then assimilated into amino acids (the building blocks of proteins), nucleotides (the building blocks of DNA and RNA as well as the important energy molecule ATP), and other cellular constituents such as vitamins, flavones, and hormones. Their ability to fix gaseous nitrogen makes legumes an ideal agricultural organism as their requirement for nitrogen fertilizer is reduced. Indeed high nitrogen content blocks nodule development as there is no benefit for the plant of forming the symbiosis. The energy for splitting the nitrogen gas in the nodule comes from sugar that is translocated from the leaf (a product of photosynthesis). Malate as a breakdown product of sucrose is the direct carbon source for the bacteroid. Nitrogen fixation in the nodule is very oxygen sensitive. Legume nodules harbor an iron containing protein called leghaemoglobin, closely related to animal myoglobin, to facilitate the conversion of nitrogen gas to ammonia.

But in a lawn, there isn't really a way to improve conditions (naturally) without amending the soil. Adding decomposed organic matter in bulk is the way to go. It takes years, but you can also go from barren land to lawn with the use of intensive green manuring, where nitrogen fixers and mass growers are grown and plowed under for the specific purpose of improving the soil. In good soil, rye (in winter) and buckwheat (in summer) will add biomass fast. Good nitrogen fixers will include vetch (in winter) and red clover or alfalfa (in summer). There are many, many more, but these are the reliable ones I've tried that come to mind right away.

So green manuring with balances of leguminous/non-leguminous plants is the most effective means of plants building soil. In nature, what you see as topsoil is darker than the subsoil because of humus, which is amorphous decomposed organic matter. You will not get much more than a very small fraction of an inch of new humus per year in nature. Topsoil took a very, very long time to form.

Answer 2

There are many potential problems that could exist in poor soil and there are endless types of plants that can help repair poor soil. In your example of "near-barren lawn", one potentially serious problem you are likely to have is soil compaction. If that is the case, then all solutions you attempt may fail until you directly address that issue.

If you have some time, here is an excellent video that goes over 6 no-till options for building healthy soil (wood chips, straw bales, soil/compost bombing, sheet mulching, Ruth Stout method, living mulch, and hugelkultur): https://www.youtube.com/watch?v=tV6sbGWE0E4 In each other these methods the soil can improve year over year without needing to import fertilizer to do it.

Also, if your interest is more around lawns. Here is an excellent approach called "Organic Lawn Care For the Cheap and Lazy": http://www.richsoil.com/lawn-care.jsp

Answer 3

There is evidence that nitrogen fixing plants such as clover and some beans do improve nitrogen levels if the roots are left in place, but generally speaking, plants don't improve the soil while they're growing - they improve the soil when they're dying, hence a green crop, ploughed in, works in that way. Biomass or humus rich materials added to soil keep the general fertility up rather than just improving nitrogen levels alone, improve bio diversity within the soil, and increase mycorrhizal activity, but this is in the process of breaking down, not while they're actually growing.

Answer 4

Yes, living plants do provide for bacteria and fungi and other soil organisms while they are alive and thriving. Plants need bacteria, fungi and bacteria, fungi need plants. They've got a symbiotic relationship as well as a biotrophic and necrotrophic relationship.

A few reports I've read give plants credit for a 40% addition of carbon around the roots to attract bacteria/fungi! While they are alive and thriving. Plants need help to take up the nutrients critical to their survival. When we till or disturb the topsoil a lot of this carbon is released into the atmosphere as CO₂. Supposedly a huge contributor of CO₂!

Regardless, live plants feed their soil organisms. Nitrogen fixing plants as well as nitrogen fixing bacteria help the crop and soil but gets complicated. Planting legumes won't necessarily negate the need for additional nitrogen.

This report about symbiosis of plants and animal/bacteria/fungi is pretty good. Dry, but to the point (pages 191-192).

Using decomposed organic mulch is the best way to improve any soil! In fact, the only way. Just applying it to the top (controls germination of weed seeds) of the soil is all that is necessary and it makes a huge difference in one season. No mixing/digging on your part. In fact, it is better that you 'till' the soil as little as possible.

I double dig my garden beds and planting beds one time only at the very beginning. Keeping plants thriving in the soil, improves the soil. Mulch on top keeps improving the soil (decomposed organic mulch), immediately. During the winter a green cover crop is powerful! Plant in the fall after cleaning up old vegetable plants. In the spring just use a spade to turn the (clover, buckwheat, annual rye...etc.) over before the plants can go to seed, dig out drainage trenches around the bed tossing the soil on top of the turned under cover crop and allowing a good month to decompose.

A bed of soil that has been raised (due to double digging and no traffic to compact) with live plants, good decomposed organic mulch, extended release organic fertilizer and an avenue (trench) for excess water is all one needs for 'improving' the soil and having a complex, healthy ecosystem! And deep, infrequent watering.

Answer 5

If by nutrients, you mean acids, hormones and such, then yes, I'm sure most plants contribute acids and other chemicals to the soil (probably different ones from different plants), which will affect different plants in different ways. Different plants may attract different kinds of microbes, and animals, which may also affect the soil nutrients (different ways for different kinds).

Different acids and other chemicals have different effects on different things. Whether it's an improvement (and what it's an improvement for) depends, but it can be an improvement, I believe. Different acids may make different elements more or less available to different plants.

If by nutrients, you mean elements, that's another matter that other people seem to have attempted to answer, with the discussion on nitrogen-fixing. Legumes tend to have microbes that fix the nitrogen (the plants themselves don't actually do it). Some other plants, I've read, can hinder this process (such as calendula, I believe), and may not be good to plant with legumes.

I suppose a venus fly trap may catch insects, and their left-over skeletons may eventually somehow contribute to the soil.

Trees can grow deep roots to bring nutrients from way down to the surface (the trees drop their leaves, which contain nutrients from down below, which may be able to contribute to the topsoil in ways).

Because many plants have delicious fruit, they influence humans to grow them, and the humans may improve the soil as a result (as well as the plant breeding; so, it's a synergistic effect). It's kind of like a symbiotic relationship, except humans aren't actually attached to the plants.

I suggest learning about cover crops. There's more to good soil than fertility (like soil structure, and probably more stuff). Buckwheat is supposed to be a good one (but not for nitrogen fixing).

In short, the answer is yes. People usually call them cover crops if they're planting them specifically for the purpose of improving soil.

Answer 6

Comfrey is a chop and drop perennial plant that is very beneficial. The plant leaves can be cut off 2-3 times a season and used as a stinky tea or used as a mulch. There is little cellulose in the leaves so they break down quickly. The roots go deep once it is established and like trees it gets the minerals deep in the soil. It is considered invasive by some. The Hybrid variety like the Russian Comfrey Bocking 14 strain does not produce seed, but does flower. It can be propagated via root. The non-hybrids produce seed. If you consider comfrey just understand that once it is there it will be hard to remove it. Most people opt for the hybrids and put them in areas they do not till or dig in and then harvest the leaves for their gardens or for healing poultices.

To get them established I use my post hole digger and made a 4-5 deep hole and filled with compost and other soil amendments then plant the root (I use Bocking 14). They will get 2 feet wide and 1 1/2 foot tall.

Answer 7

Applicability will vary with what you consider "lawn" - some people are very grass-centric there.

Clover, particularly "Dutch White Clover" can indeed be added to a lawn in difficulty (such as described) and will, over time, benefit it, being a legume, and a nice short green mowable plant. For people that douse lawns with broadleaf "weed" killers, this does not work, as those "weed" killers will kill clover.

Answer 8

I am not a scientist, but I have been undertaking my own self funded research for 20years. I knew that in a complex arrangement with soil bacteria, legumes added nitrogen to the soil, and that the a field is left fallow, the fertility improves, thanks to the work of weeds! I was determined to discover the role of individual plants. My discoveries are ignored by scientists, but I have taught thousands of students in India and Nepal how to develop their 'Sixth sense' and discover answers to all sorts of questions. This started with an interest in 'water divining' - a subject discounted out of hand by scientists. This is very frustrating as, just like animals, we are all born with this amazing gift, which I suspect, science will never be able to explain. With the ability to divine for water, not just on the ground, but over maps, sketches or Google Earth images of locations anywhere in the world, I wondered what other answers might be obtained by divining. I discovered that, when I ask to be shown a representation of an particular element, a single diving rod will rotate in ones hand to align itself to a specific compass bearing. Thus I drew up what I call 'My Circle of Elements'. Once one has done this - and with patience anyone can do it - one simply asks to be shown which element/s particular plants add to the soil. Clearly they must be harvested from the atmosphere, used for the construction of their biomass etc and modified within them presumably, with oxygen related back into the atmosphere and other exudates into the soil. The first discover was that the role of lavender is to add boron to the soil. This is such an important element for plants growing on the nutrient deficient soils of Western Australia. African lovegrass was introduced to Australia at some time in the past, and it grows rampantly - and is a real pest. Thinking laterally - I thought rampantly growing plants are possibly doing so to address a deficiency of a particular element or elements in the soil. Thus it was determined that it adds magnesium to the soil. I thought that if I provide magnesium in the form of Epsom salts, maybe I cold put the weed out of work! And this is exactly what has happened! Simply by adding a very important, low-cost trace element to the soil, I have killed this highly invasive weed. So we should not look at a weed as 'an enemy', but as Nature's way of trying to help us. I am now working on how to address other highly invasive weeds in the same way. Out of interest - while I cannot recall at this moment which elemets hemp adds to the soil,I recall there are five. It is little wonder that after a hemp crop, wheat performs vastly better.

Answer 9

I have read that hemp will replenish nitrogen and nutrients in soil.