How much CO2 do plants absorb when growing?

[Jrr1]

Hi All

I am new to this forum and I am hoping someone here can help me.
The question is, "How much CO2 do plants absorb when growing?" In other words, in 1 tonne of dry plant material, how much of it started out as atmospheric CO2?

The reason I ask is this.

I live in New Zealand where the government is trying to bring in an Emissions Trading Scheme.(ETS.) Methane emmissions from ruminants (cows and sheep, deer and goats) are going to be included in the ETS. Farmers are to pay for their emissions. Methane, "a potent greenhouse gas", is produced by bacteria in an animal's gut during the digestion of their feed.


In making their calculations they take account of the greenhouse gasses put into the atmosphere but take no account of the CO2 taken out as the plants grow.

I maintain that the whole process is at the very worst carbon neutral. By this I mean that Atmospheric CO2 is absorbed by plants as they grow. Some of this CO2 is tranferred into the livestock when they feed. Some is returned to the atmosphere as methane. According to the National Institute of Water & Atmospheric Research (NIWA) , a dairy cow produces about 75 kg of methane per cow per year. http://www.niwa.cri.nz/ncces/projects/ghge/agricultural

In New Zealand, a milking cow on a pasture only diet eats about 16 kg dry matter per day or 5840 kg per year. American grain fed animals eat more.

The amount of carbon put into the atmosphere (as methane) must necessarily be less than the carbon taken out (during photosynthesis) but to work it out I need to know what percentage of the plant came from atmospheric CO2.
The fact that they have left out this from their calculations shows me the ETS has been very poorly thought out.

I am sure someone has already worked this out.

[CO2Realist]

The Formula for photosynthesis is:

6CO2 + 6H2O = C6H12O6 + 6O2
264 108 180 192

That is all the plant has going for it in food / energy terms.
Once it has the glucose, everything else in the plant is made by the plant from the glucose.

You could consider the formula for the methane produced from the digestion process as:

C6H12O6 = 3CH4 + 3CO2
180 48 132

So very approximately, in simple terms:
9ozs of CO2 are removed from the atmosphere to make 6ozs of animal fodder which ferments in the gut to produce 2ozs of methane and 4ozs CO2
It also uses 4ozs of water but gives you 6ozs Oxygen

Hope that helps

[eadler2]

The Formula for photosynthesis is:

6CO2 + 6H2O = C6H12O6 + 6O2
264 108 180 192

That is all the plant has going for it in food / energy terms.
Once it has the glucose, everything else in the plant is made by the plant from the glucose.

You could consider the formula for the methane produced from the digestion process as:

C6H12O6 = 3CH4 + 3CO2
180 48 132

So very approximately, in simple terms:
9ozs of CO2 are removed from the atmosphere to make 6ozs of animal fodder which ferments in the gut to produce 2ozs of methane and 4ozs CO2
It also uses 4ozs of water but gives you 6ozs Oxygen

Hope that helps

Thank you for that analysis, but it needs to be completed to determine the effect on global warming.
Because CH4 has a different molecular bond structure and more modes of vibration than CO2, CH4 in the atmosphere has a global warming potential 23 times as high as CO2 per Kg over a 100year period.
http://en.wikipedia.org/wiki/Global_warming_potential

So to compare the GWP of the methane and CO2 produced by the above process with the GWP of the starting 9 Oz of CO2, the ratio is (23*2+4)/9=5.5.

So it is a good idea to ferment the cow waste and burn the methane produced to get CO2.

[ceyda]

Hi All

I am new to this forum and I am hoping someone here can help me.
The question is, "How much CO2 do plants absorb when growing?" In other words, in 1 tonne of dry plant material, how much of it started out as atmospheric CO2?

The reason I ask is this.

I live in New Zealand where the government is trying to bring in an Emissions Trading Scheme.(ETS.) Methane emmissions from ruminants (cows and sheep, deer and goats) are going to be included in the ETS. Farmers are to pay for their emissions. Methane, "a potent greenhouse gas", is produced by bacteria in an animal's gut during the digestion of their feed.


In making their calculations they take account of the greenhouse gasses put into the atmosphere but take no account of the CO2 taken out as the plants grow.

I maintain that the whole process is at the very worst carbon neutral. By this I mean that Atmospheric CO2 is absorbed by plants as they grow. Some of this CO2 is tranferred into the livestock when they feed. Some is returned to the atmosphere as methane. According to the National Institute of Water & Atmospheric Research (NIWA) , a dairy cow produces about 75 kg of methane per cow per year. http://www.niwa.cri.nz/ncces/projects/ghge/agricultural

In New Zealand, a milking cow on a pasture only diet eats about 16 kg dry matter per day or 5840 kg per year. American grain fed animals eat more.

The amount of carbon put into the atmosphere (as methane) must necessarily be less than the carbon taken out (during photosynthesis) but to work it out I need to know what percentage of the plant came from atmospheric CO2.
The fact that they have left out this from their calculations shows me the ETS has been very poorly thought out.

I am sure someone has already worked this out.

Hi JRR1

There was a news story on this site from the The New Zealand Climate Science Coalition:

http://nzclimatescience.net/index.php?o ... 9&Itemid=1

Perhaps you could get in touch with them and somone there maybe sympathetic to you cause.

Good Luck

[Jrr1]

Hi There

Thanks for the help.

The numbers you have given me account for the atmospheric CO2 that is returned to the air but not all of the CO2 does this.

I grow about 6 hectares (15 acres) of maize (Americans call it corn) each year. I would normally harvest about 20000 kg per hectare which ends up being eaten by our cows. Thats a lot of CO2.

But this doesn't include the many tonnes per hectare of roots that are underground. Maize roots commonly reach 1.5 metres ( 5 feet) beneath the surface. These roots take many years to break down and over time organic material (i.e. carbon compounds) builds up in the soil.

Maize, pasture and other crops act as a carbon sink but they are completely ignored in the Emissions Trading Scheme.

A milking cow (fed mainly on pasture) in NZ would normally eat 16 kg of dry matter per day. 5840kg per year. Not all of this returns to the atmosphere.
We are told a cow produces 75 kg of methane per year.

I suppose my point is that if you don't take into account the CO2 that is being removed from the system then you only have half a budget. It is like doing a financial budget but only looking at the expenses and ignoring the income.


I am hoping the general population will realise AGW is based on shonky science before this ETS does too much damage.

Thanks again for your input.

[CO2Realist]

Hi Jrr1,
Pardon the expression but are you saying you are about to get taxed on cow farts?
This ETS is just b******t, or oxex, as I prefer to call it.
Just think about the millions of buffalo that roamed the planes of America before the railroaders ate them all. No doubt they all farted like thunder.
Similarly the millions of wilderbeasts in Africa, and as for the elephants. Ye gods! You could have powered a small city on their gaseous effluvia.

But to return to your problem.
If your harvest of about 20000 kg per hectare is 'everything above ground' and fed to your cows then to allow for 'all below ground' I would start with a figure of double. If your harvest yield is made up of just the corn-cobs then four times the plant material has been grown. But what do you do with the stems and leaves? If you burn it at harvest then that's 25% CO2 returned to the atmosphere in the same year.
Oh! By the way, you cannot include the water element of the harvest yield which probably accounts for 50% of the mass.

[Infrared]

Some people think the buffalo that roamed the planes (sic) of America are still doing it. You'd think so too, if you'd recently flown anywhere in the States! (Making a funny.)

[eadler2]

Hi There

Thanks for the help.

The numbers you have given me account for the atmospheric CO2 that is returned to the air but not all of the CO2 does this.

I grow about 6 hectares (15 acres) of maize (Americans call it corn) each year. I would normally harvest about 20000 kg per hectare which ends up being eaten by our cows. Thats a lot of CO2.

But this doesn't include the many tonnes per hectare of roots that are underground. Maize roots commonly reach 1.5 metres ( 5 feet) beneath the surface. These roots take many years to break down and over time organic material (i.e. carbon compounds) builds up in the soil.

Maize, pasture and other crops act as a carbon sink but they are completely ignored in the Emissions Trading Scheme.

A milking cow (fed mainly on pasture) in NZ would normally eat 16 kg of dry matter per day. 5840kg per year. Not all of this returns to the atmosphere.
We are told a cow produces 75 kg of methane per year.

I suppose my point is that if you don't take into account the CO2 that is being removed from the system then you only have half a budget. It is like doing a financial budget but only looking at the expenses and ignoring the income.


I am hoping the general population will realise AGW is based on shonky science before this ETS does too much damage.

Thanks again for your input.

Hi There

Thanks for the help.

The numbers you have given me account for the atmospheric CO2 that is returned to the air but not all of the CO2 does this.

I grow about 6 hectares (15 acres) of maize (Americans call it corn) each year. I would normally harvest about 20000 kg per hectare which ends up being eaten by our cows. Thats a lot of CO2.

But this doesn't include the many tonnes per hectare of roots that are underground. Maize roots commonly reach 1.5 metres ( 5 feet) beneath the surface. These roots take many years to break down and over time organic material (i.e. carbon compounds) builds up in the soil.

Maize, pasture and other crops act as a carbon sink but they are completely ignored in the Emissions Trading Scheme.

A milking cow (fed mainly on pasture) in NZ would normally eat 16 kg of dry matter per day. 5840kg per year. Not all of this returns to the atmosphere.
We are told a cow produces 75 kg of methane per year.

I suppose my point is that if you don't take into account the CO2 that is being removed from the system then you only have half a budget. It is like doing a financial budget but only looking at the expenses and ignoring the income.


I am hoping the general population will realise AGW is based on shonky science before this ETS does too much damage.

Thanks again for your input.

Jrr1,
There is some literature on this. Unfortunately I haven't been able to locate any numbers you can use to make your case. The amount of carbon sequestered when roots are left in the soil seems to depend on whether the soil is tilled or not and other soil conditions.

I used the words - corn growth sequestered carbon roots , in a Google search. Here is one of the papers I found.
http://www.ias.ac.in/currsci/oct102006/885.pdf
Monsanto advertises that no till practices will increase carbon sequestration and claims that farmers use this practice for credits in the US.

http://www.monsanto.com/responsibility/our_pledge/healthier_environment/carbon_sequestration.asp

Depending on their farming practices, farmers can actually reduce carbon dioxide in the air. Plants take in carbon dioxide and use it to build roots, stalks, grain, and other parts. If farmers minimally till their fields before planting, much of that carbon remains in the soil. Farmers can sell this sequestered carbon as credits on the Chicago Climate Exchange. “This incentive encourages more farmers be an integral part of efforts to reduce greenhouse gas emissions,” Steiner said.

Here is a paper that claims:"Organic Farming Sequesters Atmospheric Carbon and Nutrients in Soils"
http://www.strauscom.com/rodale-whitepaper/

But another paper says that no till farming does not help carbon sequestration.
http://cnmp.unl.edu/Jan%2024%20Inservice/2006%20AEE%20Baker%20tillage%20and%20soil%20C%20sequestration.pdf
"It is widely believed that soil disturbance by tillage was a primary cause of the historical loss of soil organic carbon (SOC) in North
America, and that substantial SOC sequestration can be accomplished by changing from conventional plowing to less intensive methods
known as conservation tillage. This is based on experiments where changes in carbon storage have been estimated through soil sampling of
tillage trials. However, sampling protocol may have biased the results. In essentially all cases where conservation tillage was found to
sequester C, soils were only sampled to a depth of 30 cm or less, even though crop roots often extend much deeper. In the few studies where
sampling extended deeper than 30 cm, conservation tillage has shown no consistent accrual of SOC, instead showing a difference in the
distribution of SOC, with higher concentrations near the surface in conservation tillage and higher concentrations in deeper layers under
conventional tillage. These contrasting results may be due to tillage-induced differences in thermal and physical conditions that affect root
growth and distribution. Long-term, continuous gas exchange measurements have also been unable to detect C gain due to reduced tillage.
Though there are other good reasons to use conservation tillage, evidence that it promotes C sequestration is not compelling"

One paper I found says that feeding cattle grass is the best way to help carbon sequestration.
http://www.botanicgardensblog.com/index.php/2008/07/22/feel-good-about-eating-grass-fed-meat/

I think the lack of definitive numbers makes it hard to really build a case. Maybe you can find something if you follow up more thoroughly than I have done.

[CO2Realist]

Some people think the buffalo that roamed the planes (sic) of America are still doing it. You'd think so too, if you'd recently flown anywhere in the States! (Making a funny.)

Sorry! Slip of the brain. I only fly in Britsh Airways, or in that nice Mr Branson's planes. I had forgotten they are not allowed to fly over the plains of 'The Colonies'. Damn that Tea Party.

[Jrr1]

Hi Co2Skeptic

Yes I am afraid they are going to tax our cows farts. Strictly speaking though most of the methane is in the belching. However it is most certainly bull manure.

I've been thinking about nominating Buffolo Bill for a Nobel Peace prize for his efforts to reduce greenhouse gas emmissions in the nineteenth century. Shooting thousands of Buffalo must have helped.

Everything that is harvested becomes fodder. Leaves stalks and cobs get shredded and ensiled. Bacterial anaerobic fermentation lowers the ph to about 5.5
This prevents rotting and allows it to be stored for years if necessary.

The 20000 kg/ha is just dry matter. That is not including water.

Hi Eadler2

Thanks for the references. I think there has not been much research on soil carbon sequestration. The science is not settled.

I liked the one on feel good about grass fed meat as our cows are never housed in barns and spend their entire lives outside grazing on pasture. I never snows where I live although there has been snow this year on some nearby hills. This has not happened sine the 1970's

We supplement the cows diet during summer with turnips and with maize silage in winter and spring. However 80 to 90% of their diet is grass. I suspect that the carbon sequestration of pasture will be less than for deep rooting crops like maize, but I also suspect it could be considerable.

I also think it is irresponsible of our government to enact economically damaging legislation when their are so many uncertainties.

Thanks again for your interest and help.