Can increasing soil carbon also increase soil CO2 back into atmosphere?

N.Yorks.

Member
Finally decided to sit down and try and get my head around 'banking soil carbon' and the whole soil C sequestration thing.

We are trying to increase soil organic matter (OM) levels for all the positive benefits that go with that - better soil structure, better drainage, better nutrient cycling, better moisture retention and greater resilience to compaction etc. So far so good, all postive stuff!

Increasing soil OM also increases soil carbon.

Are we inadvertantly accelerating the conversion of soil carbon into CO2 that comes from respiration of the increased soil OM/C levels?
To increase soil C we're putting more crop residue and plant material into the soil 'breakdown system' driven by soil microbes, but these microbes are operating at a higher rate due to more OM and potentially warmer soils, thereby respiring carbon back into the atmoshere as CO2 at a greater rate.

Will the drive to bank soil carbon actually have the opposite effect or at best have very little net effect? Looking forward to the collective thoughts on here!
 
I think the old humus stays in the soil for hundreds of years idea has been updated, I think now the latest thinking is it's more of a dynamic system (Carbon in, Carbon out, but still more held in the soil), I think ultimately the more we can encourage fungi, as opposed to bacteria to dominate the soil biome the more Carbon is held in the soil. I am not sure how Tera Petra soils (in the Amazon) and Bio Char fit in this, maybe, Bio Char holds far more Carbon than anything else in the soil, if we can find a way of getting more of it into the soil in a commercial setting. I think too much cultivation is bad for fungi, which ultimately is bad for soil holding onto Carbon.

Also recently heard that as we pull Carbon from the atmosphere, so the oceans give up Carbon, but ultimately, the more we can sequester in the soil the better.

I think the best way to sequester Carbon is with mob grazing and getting the soil biome "buzzing", any cultivation is bad for that, however, we still need to eat grains etc so there has to be a compromise on this, but probably cut out ploughing (mind you I guess you still have to for Potatoes etc), so again, compromise.
 
Finally decided to sit down and try and get my head around 'banking soil carbon' and the whole soil C sequestration thing.

We are trying to increase soil organic matter (OM) levels for all the positive benefits that go with that - better soil structure, better drainage, better nutrient cycling, better moisture retention and greater resilience to compaction etc. So far so good, all postive stuff!

Increasing soil OM also increases soil carbon.

Are we inadvertantly accelerating the conversion of soil carbon into CO2 that comes from respiration of the increased soil OM/C levels?
To increase soil C we're putting more crop residue and plant material into the soil 'breakdown system' driven by soil microbes, but these microbes are operating at a higher rate due to more OM and potentially warmer soils, thereby respiring carbon back into the atmoshere as CO2 at a greater rate.

Will the drive to bank soil carbon actually have the opposite effect or at best have very little net effect? Looking forward to the collective thoughts on here!

Are you interested in this from the point of view of looking after your soil/ farm for its own sake or from the point of view of banking carbon?
 

N.Yorks.

Member
Are you interested in this from the point of view of looking after your soil/ farm for its own sake or from the point of view of banking carbon?
The concept of banking carbon got me intereested, as I thought that it was too simplistic to assume that just by increasing soil OM & C we reduce atmospheric CO2.

There are a huge number of soil organisms and the more OM/C you send them the busier they get and the more active they are the more they respire CO2 back out of the soil. Was trawling the scientific leterature and it seems that warmer soils of the future will also drive this higher rate of soil respiration.

I'm thinking that we don't know enough to start selling soil carbon credits - it's very uncertain what the net effects are. A waterlogged upland peat soil accumulates carbon as it is generally anaerobic, but no productive arable/grassland soil should be like that.
 

CornishTone

Member
BASIS
Location
Cornwall
It’s a great question. I think ultimately increased OM will have have a positive impact on soil biology and all that respiration means the carbon cycle is more active. When this is working right it should be a largely cyclical process with carbon entering the cycle via growing plants taking in C02 and exiting via biological decomposition and respiration. Some of that carbon will “stick” in the soil in the form of humus. The more carbon we can push into that dynamic and active cycle, the more we can hopefully get to stick.

It’s worth remembering that an actively growing plant only takes 80% of its C02 from the atmosphere, the other 20% is coming up from the soil, meaning there’s a nice little feedback loop directly from soil to plant and back again. This loop is broken the moment you stop having a growing plant covering the soil. The biology goes on respiring and releasing C02 but there’s not plant to catch it on it’s way up. This is part of the reason that maintaining soil cover with living plants is so important.
 

N.Yorks.

Member
Are you interested in this from the point of view of looking after your soil/ farm for its own sake or from the point of view of banking carbon?
Of course increased soil OM/C leads to a better soil which will be more productive and has so much going for it, but selling C credits may be a step too far in many circumstances.
 
I have also heard that increasing soil carbon increases water infiltration rates and the amount of water a soil can hold as well, so it's a better way of reducing water flow off land during high rainfall events and thus reduce flooding down stream, maybe this should also be pointed out to the "eat less meat for global warming" brigade, maybe we should change what they are saying to "eat less meat to increase flooding of towns and cities"!!!
 

N.Yorks.

Member
It’s a great question. I think ultimately increased OM will have have a positive impact on soil biology and all that respiration means the carbon cycle is more active. When this is working right it should be a largely cyclical process with carbon entering the cycle via growing plants taking in C02 and exiting via biological decomposition and respiration. Some of that carbon will “stick” in the soil in the form of humus. The more carbon we can push into that dynamic and active cycle, the more we can hopefully get to stick.

It’s worth remembering that an actively growing plant only takes 80% of its C02 from the atmosphere, the other 20% is coming up from the soil, meaning there’s a nice little feedback loop directly from soil to plant and back again. This loop is broken the moment you stop having a growing plant covering the soil. The biology goes on respiring and releasing C02 but there’s not plant to catch it on it’s way up. This is part of the reason that maintaining soil cover with living plants is so important.
I remember listening to a US soil scientist who thought that increased soil OM and subsequent increased soil microbe respiration increased the concentration of CO2 in the crop canopy and had the potential to boost yields.

I'm thinking increased soil C isn't the answer to curbing atmospheric CO2 levels.

Woodland/forest planting would have a longer term effect as C is stored in wood/lignin but it depends where that timber ends up long term.....

Think the answer is to stop digging up C from the earths crust and leave it where it can't do harm.
 

cb387

Member
Arable Farmer
Location
Glos
In my simplistic view (which is probably wrong) the carbon gets captured as a crop grows and then released as it breaks down /used. It’s a cyclical thing? The carbon that was once locked in soil / plants pre agriculture days is already in the atmosphere or plant depending on the time of year. We aren’t really releasing more, just really moving it around. It’s burning fossil fuels that is significantly increasing carbon in the atmosphere long term
 
I remember listening to a US soil scientist who thought that increased soil OM and subsequent increased soil microbe respiration increased the concentration of CO2 in the crop canopy and had the potential to boost yields.

I'm thinking increased soil C isn't the answer to curbing atmospheric CO2 levels.

Woodland/forest planting would have a longer term effect as C is stored in wood/lignin but it depends where that timber ends up long term.....

Think the answer is to stop digging up C from the earths crust and leave it where it can't do harm.
I have read that when you plant trees on grassland, the changes to the soil biome causes Carbon to be emitted from the soil (this is eventually equalised by the Carbon being stored in the wood), but if the trees are eventually burnt or allowed to rot, the whole thing is far worse than rotationally grazed pasture, and this is not even thinking of planting trees on peat!

Old woods I think should never be cut down, but we need to be very careful where we plant new woodland, and when we do, what we plant, otherwise it is far worse than what is already there.
 

N.Yorks.

Member
In my simplistic view (which is probably wrong) the carbon gets captured as a crop grows and then released as it breaks down /used. It’s a cyclical thing? The carbon that was once locked in soil / plants pre agriculture days is already in the atmosphere or plant depending on the time of year. We aren’t really releasing more, just really moving it around. It’s burning fossil fuels that is significantly increasing carbon in the atmosphere long term

Think you're right in that the OM/C you stick into the soil determines what you get back, totally cyclical. So by that logic if you stick more carbon into the soil it'll bung a bit more out. Think there will be a lag as a lot of OM isn't broken down so fast.....
 

CornishTone

Member
BASIS
Location
Cornwall
I remember listening to a US soil scientist who thought that increased soil OM and subsequent increased soil microbe respiration increased the concentration of CO2 in the crop canopy and had the potential to boost yields.

I'm thinking increased soil C isn't the answer to curbing atmospheric CO2 levels.

Woodland/forest planting would have a longer term effect as C is stored in wood/lignin but it depends where that timber ends up long term.....

Think the answer is to stop digging up C from the earths crust and leave it where it can't do harm.

I have read that when you plant trees on grassland, the changes to the soil biome causes Carbon to be emitted from the soil (this is eventually equalised by the Carbon being stored in the wood), but if the trees are eventually burnt or allowed to rot, the whole thing is far worse than rotationally grazed pasture, and this is not even thinking of planting trees on peat!

Old woods I think should never be cut down, but we need to be very careful where we plant new woodland, and when we do, what we plant, otherwise it is far worse than what is already there.
There's plenty of work being done on this now. Permanent grassland has been shown to store as much carbon as established woodland and we don't need to do anything other than just leave it alone. But where do people want to plant their trees? On permanent pasture which is seen as less "productive". Trouble is, the moment you dig a hole to plant a tree, you release carbon stored in the soil beneath. That grassland is no longer managed/grazed so grows long and rank and becomes a source of chemical decomposition rather than biological decomposition so releases C. Eventually the tree shades out the grass (or whatever understory establishes in its place) which stops fixing carbon, leaving only the tree. This means the tree actually takes many, many years to offset it's own carbon footprint before it can ever hope to offset anyone else's. Then there's the issue of "safe carbon". Trees can burn, so releasing their carbon. Soil, if left alone, will hold i's carbon no matter what, particularly if its stored nice and deep.

It's far more complex than just "plant some trees". If only people would just leave grass to do what it does best! Of course, there's an agenda at play here. Grass feeds ruminants, as it has done for millions of years, and they are dreadfully unfashionable at the moment. Trees are in fashion so it's "plant trees at all costs and stop cows eating"!
 

CornishTone

Member
BASIS
Location
Cornwall
Think you're right in that the OM/C you stick into the soil determines what you get back, totally cyclical. So by that logic if you stick more carbon into the soil it'll bung a bit more out. Think there will be a lag as a lot of OM isn't broken down so fast.....
It'll not be truly cyclical if the system is working correctly. Some will always get left behind or you'd never build any organic matter... or never would've lost it in the first place for that matter.
 

bactosoil

Member
While there is a huge amount of research being done on Carbon storage and soil bacteria and fungi with terabytes of data being harvested we actually know still so little about just bacteria alone in soil ( estimated at 5-8 % of soil bacteria has been studied in any depth todate )
If soil does have a biological makeup akin to our human dna profiles this adds to further variables , one thing that appears to help keep carbon in the soil is biological balance , any spike caused by say a nutrient oversupply /overload can cause a rapid depletion of carbon in all forms
 
While there is a huge amount of research being done on Carbon storage and soil bacteria and fungi with terabytes of data being harvested we actually know still so little about just bacteria alone in soil ( estimated at 5-8 % of soil bacteria has been studied in any depth todate )
If soil does have a biological makeup akin to our human dna profiles this adds to further variables , one thing that appears to help keep carbon in the soil is biological balance , any spike caused by say a nutrient oversupply /overload can cause a rapid depletion of carbon in all forms
this is why I have read the Roundup is so bad for soil, as it is an antibiotic and kills the soil bacteria
 
would I be right in thinking then, roundup kills soil bacteria, this then causes them to decompose and give off their held Carbon? Would that then mean, the unintended consequences of GM/Roundup ready seeds is the death of the soil biome and increased global warming?
 

cows sh#t me to tears

Member
Livestock Farmer
There's plenty of work being done on this now. Permanent grassland has been shown to store as much carbon as established woodland and we don't need to do anything other than just leave it alone. But where do people want to plant their trees? On permanent pasture which is seen as less "productive". Trouble is, the moment you dig a hole to plant a tree, you release carbon stored in the soil beneath. That grassland is no longer managed/grazed so grows long and rank and becomes a source of chemical decomposition rather than biological decomposition so releases C. Eventually the tree shades out the grass (or whatever understory establishes in its place) which stops fixing carbon, leaving only the tree. This means the tree actually takes many, many years to offset it's own carbon footprint before it can ever hope to offset anyone else's. Then there's the issue of "safe carbon". Trees can burn, so releasing their carbon. Soil, if left alone, will hold i's carbon no matter what, particularly if its stored nice and deep.

It's far more complex than just "plant some trees". If only people would just leave grass to do what it does best! Of course, there's an agenda at play here. Grass feeds ruminants, as it has done for millions of years, and they are dreadfully unfashionable at the moment. Trees are in fashion so it's "plant trees at all costs and stop cows eating"!
How about lucerne? Fixes nitrogen as well.
 

cows sh#t me to tears

Member
Livestock Farmer
would I be right in thinking then, roundup kills soil bacteria, this then causes them to decompose and give off their held Carbon? Would that then mean, the unintended consequences of GM/Roundup ready seeds is the death of the soil biome and increased global warming?
Our nutritionist hates roundup for that very reason. Kills the bugs in the soil. No good for biodynamic farming.
 

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