There is this strange dichotomy between the permaculture world and that of conventional approach regarding the need for carbon in soil. Permie world seems to say you need high amounts of carbon, yet the conventional class says all carbon can be accessed by the plant through the atmosphere. Part of the debate, if I understand correctly, is from the permie side carbon is synonymous with either life, as in bacteria, or in decaying life, such as plant matter. Therefore it is seen as an overall facilitator for healthy soils as opposed to simply an inert chemical commodity to be extracted by root tips. So if I have any of this wrong please correct me. But my basic question is- "Do plants take up carbon from the soil in significant quantities?" If so, why is there no discussion of this from conventional growers?
Carbon in the soil, through the action of soil biota, creates humus which provides plants with nutrients in a form they can use. This is basic soil science.
"By breaking down carbon structures and rebuilding new ones or storing the C into their own biomass, soil biota plays the most important role in nutrient cycling processes and, thus, in the ability of a soil to provide the crop with sufficient nutrients to harvest a healthy product. The organic matter content, especially the more stable humus, increases the capacity to store water and store (sequester) C from the atmosphere."
Organic matter in soils, which is mostly carbon compounds, is a huge benefit not only to the soil biota but to what one might call the sponginess of the soil.....it's ability to absorb, retain, and release air, water, and nutrients of all kinds. The classic improvement to both a tight clay soil and a complete sand soil is to add all the organic matter possible. Also, this organic matter is a major pathway to sequester carbon from the atmosphere (where it's current excess is causing climate change). Moving carbon from the air and into the soil benefits both, and almost always improves plant growth. That said, large amounts of uncomposted or uncharred carbon mixed in the soil can cause a temporary nitrogen deficiency as soil microbes take up nitrogen as they multiply on the carbon substrate. Adding a high nitrogen input like urine, or simply leaving the organic matter on the surface as a mulch rather than incorporating it (worms and such will do it for you anyway, and at a pace in balance with the soil's nitrogen budget), will prevent this.....
To answer your question, plants take up carbon from the air as they grow, and deposit it in the soil as they decay. Plants are the main pathway on land for moving carbon out of the air and into the soil. Microbes use soil carbon, and gradually move it back into the air....a process which in most temperate climates is slower than the movement of carbon the other way by plants and leads to a gradual buildup of carbon in the soil..... The humid tropics are different....there, these processes are in balance and most of the accumulated carbon is in the living and dead vegetation and never really makes it into the soil. This is one reason why destroying rainforest is extra damaging....there is less reserve of organic matter in the soil to jumpstart it's regrowth
It would seem that plants can get all the carbon they need from the atmosphere. The photosynthesis equation goes like this:
6CO2 + 6H2O + light → C6H12O6 + 6O2.
Or put simply:
Carbon Dioxide + Water in the presence of Light = Carbohydrates and Oxygen.
So the place of carbon in the soil is about something else. Permiculture and conventional agriculture perhaps have different starting points and as well as different goals. By increasing organic matter/carbon in the soil, the permiculturist is improving soil fertility, soil structure, soil flora and fauna and increasing water holding capacity of the soil- etc , or in another words the permiculturist is primarily concerned with sustainability of the system: the long term health of the soil system, which will ensure the long term viability of his/her and future generations of future yield. Organic matter in the soil is the best way to achieve these goals. Conventional agriculture doesn't need healthy soil because it can achieves its goals on the basis of cheap inputs made possible by cheap fossil fuel. It is concerned with getting the highest yield for the the least amount of money invested. Check out this on you tube
(Watch the whole programme because it is really excellent stuff! but from 7.00 shows how much oil goes into our food) Because fossil fuel is so relatively cheap ( for the moment) a fossil fuel based agricultural system is the best way (for the moment) to achieve a high yeild for little cost, while it is relatively more expensive to achieve those same goals organically. That's why organic food is more expensive. And that is why peak oil should be of concern to us all. As oil becomes more difficult and expensive to extract the price of energy will start to rise. The economics between the two systems may change dramatically. Especially as the soils farmed conventionally have been degraded by its methods and are totally reliant on cheap fossil fuel inputs to make them productive. Listen to Jeremy Grantham who is a commodity trader (ie he is very much a capitalist) yet he is extremely concerned about some of the unsustainable aspects of capitalism especially that of how we farm and treat the soil. He talks about a 'deal the farmer has made with the devil.'
!st yes it is true that trees get all their carbon from the air and not from the soil.
However carbon in the soil make the soil porous and in that state the tree roots and grow faster to access more minerals that they do need from the soil.
The porous soil also hold more water than non-porous soil.
The carbon in the soil also helps hold mineral vs just letting the rain wash it all away.
If you give critter like worms carbon(leaves) they will eat it and in return digg plenty of holes, which un-compacts the land, aerating it.
The carbon that we are talking about come from plant leaves/etc. And these plant parts contain not just carbon, but potassium, phosphorous, calcium, sulfur, etc, that previous trees have mined from deep in the soil (15ft) and have deposited on the surface which seedling with baby roots can now use.
Plants also have a secondary sets of root. That covers a much wider and deeper area than the primary roots. These roots are the mycelium of mycorrhizal fungi. The mycelium increases the efficiency of water and nutrient absorption of most plants and confers resistance to some plant pathogens.
Location: Grand Valley of Colorado's Western Slope
posted 6 years ago
Yeah, why we need carbon in the soil is because we want to maintain a biosphere here on earth that is friendly to OUR kind of organism.
The CO2 that is in the soil is therefore NOT in the atmosphere. The bio-cycle (plants capturing CO2 which is eaten or left in the soil has the potential to clear out the excess PPM of CO2 in a short time.
I am passionate about this. This gives me hope that we can actually do something other than wait around for the so called experts to solve the situation. Just trying to have a small to zero carbon foot print won't do enough to get us back where we need to be. IMO, it is ALL about soil carbon.
Peter Donovan is working hard through the soil carbon coalition to spread the word, and encourage small holding land stewards as well as large holders to boost soil carbon.
and there was a great book published in 2013 connecting soil carbon to flood drought cycles, climate change and the "work" accomplished by solar driven photosynthesis. The book is called "Cows Save the Planet" by Judith Schwartz. here is a link to the Soil Carbon Coalition review and description of the book http://soilcarboncoalition.org/taxonomy/term/3
My library has a copy, but I also got a used copy pretty cheap from Abe Books, my favorite online bookstore. Actually I've bought several copies so I can lend them around, it is that important to me that the word is spread.
If you go to this link http://soilcarboncoalition.org/files/htmlquery.htm and at the bottom, type in CWF (has to be all caps) you can see the photos taken the day Peter Donovan tested my soil for pre-existing carbon. You can see the soil is almost not soil. The total carbon (which includes mineral carbon such as calcium carbonate, a salt which makes the soil alkaline) is 1.4 %. If you take away the CaCO3 ( I think that's calcium carbonate) I probably have about 2/3 of one percent organic carbon. My trial will finish in ten years, and I am hoping to have managed to get literally tons of CO2 out of the air and into my ground, because of all that happens when the soil is rich in organic carbon (as opposed to mineral carbon.)
I have been working in other parts of my place. It all started out that impoverished, but the place Peter tested is more like what I started with. After he tested, I began to try to build soil carbon in that part of the property, just through planting deep rooted grasses, which I will have grazers eat, or mow periodically. I have planted some C4 grasses, well, several species of C4 plants, in addition to existing C3 plants.
yes, passionate aobut this. Go soil carbon!
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