CO2: Is mowing his lawn a citizen gesture?

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Christophe
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CO2: Is mowing his lawn a citizen gesture?




by Christophe » 16/06/15, 19:46

Little common reflection on CO2: is it interesting from a CO2 point of view to mow your lawn?

A first approach will say that it is necessarily negative since we use (most of the time) gasoline to mow.

Only a mowed lawn grows better and will therefore re-store carbon. Mowing waste is stored carbon provided that the mowing waste does not ferment into methane, of course, but this is rarely the case ...

So here, if we could make, together, a small estimate (which will necessarily be quite imprecise), that would be nice.

Figures to start with: average fuel consumption per mowed area and CO2 stored by mowed grass on the same area ... :?:
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by chatelot16 » 16/06/15, 21:34

whether the mowed grass is methanising, rotting or composting, it ends up in CO2

it is only if the grass was used for energy purposes by methanization while saving other energy than that would be positive

a decade ago I had started methanization and had found that the gasoline consumed by an average mower is low compared to the methane that we could produce with grass ... but we need a methanizer which works well and which pays for itself all year round with waste other than grass

except methanisation the lawn does not capture carbon ... the mower is only one more energy consumption for aesthetics

we can also let the grass grow high enough to mow and make hay for the cattle: it does not make energy but it feeds useful animals which is even more valuable
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by moinsdewatt » 16/06/15, 21:40

Lawn mowing at best finished in CO2 after degradation and at worst in CH4.

If we didn't talk about CH4, a lawn would be CO2 neutral over time.

It's not like peatlands where carbon builds up in the roots for centuries.
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by chatelot16 » 16/06/15, 22:33

I confirm ! it is only in peat bogs that it stores carbon ... when it rots or compost carbon returns to CO2

fortunately when it rots it does not methanize ... to methanize you need a rigorous lack of oxygen which is quite rare so that there is no undesirable methanization

methanization is only useful if methane is well used to save oil ... if methane is lost in the atmosphere it is catastrophic given the greenhouse effect of methane much worse than CO2
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by Did67 » 17/06/15, 09:32

I am of the same opinion, with one nuance: the large piles of grass which ferment "methanize" well in part, because a fairly impermeable layer is formed on the surface by compaction, and an "anaerobic" zone below ...

So there, in addition to the CO² balance, is added the impact in terms of "greenhouse effect" [global warming], which is generally measured by equivalent CO² ...

So, yes, a lawn mowed close to the ground or mowed once a year, in balance somehow, it is neutral at first sight.

In detail, in reality, there is under the lawn, a humification process (production of humus), which is a sequestration of C on a human time scale (the humus itself decomposes, but very very slowly; when a soil goes from a stable state low in humus to a stable state rich in humus, it stores C.

It is more important if one mows "old hay", more cellulosic. The young grass, more fermentable, gives almost no humus ...

On the scale of French agriculture, the quantities involved are enormous (but at the moment, "mineral and fossil-fueled agriculture - mineral fertilizers, tractor plowing ..." tends to impoverish the soil in humus. , therefore we are destocking !).

AND indeed, the grass clippings are methanisable ... We then recover the solar energy captured by the lawn. The C balance sheet is neutral (except for gray energy).
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by Christophe » 17/06/15, 11:32

Is that so? So the calculation is quickly done: CO2 + CO2 = CO2 :D

But damn, is there not a small part of the cut grass that ends in humus ????

For methane, we talked about it in another subject a long time ago and many claimed that under domestic conditions (say a heap less than 1 m high) it was not possible to have anaerobic methanization conditions. ..
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by Did67 » 17/06/15, 14:44

There is generally methane: see this Swiss document concerning the composting of organic waste

http://www.ader.ch/energieaufutur/energ ... mposte.php

There is that too:

http://www.passerelleco.info/article.ph ... ticle=1365

Or even this "Composting represents an effective solution to highlight what is biodegradable and which is found in a proportion of more than 40% in all residual materials. But beware, composting releases large quantities of methane. , a gas whose heating power is 21 times greater than that of CO2. " in : http://www.transition-energie.com/trans ... /biomasse/

OR again this: But, if we bury the plant residues, it is no longer the same bacteria that will degrade the plant: the bacteria that live in an anaerobic environment, that is to say without oxygen, produce methane rather than carbon dioxide through their digestion. "

OR again: "However, the greenhouse effect attributed to methane is 30 times greater than that of carbon dioxide. Home composting therefore translates into a real gain in the fight against GHGs, but on condition that it is very well ventilated. " in : http://www.iforum.umontreal.ca/Forum/20 ... nce_1.html

So I sincerely think that the pile of grass mowing that is left to rot in a corner is a source of methane (we are far from the conditions for correct composting: balanced C / N ratio; controlled humidity; turning and aeration; mixing fibrous masses and rods, etc. with more compact masses ...)
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by moinsdewatt » 17/06/15, 17:01

Christophe wrote:Is that so? So the calculation is quickly done: CO2 + CO2 = CO2 :D

But damn, is there not a small part of the cut grass that ends in humus ????


But have you not already destroyed the preexisting humus in the establishment of this lawn ???

In which case this lawn only recreates the humus that there was before being destroyed .....
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by Did67 » 17/06/15, 17:36

The assessment is not so simple!

There is sequestration if the humus level increases between an instant A and an instant B ... The variations in the humus levels of the soil are very slow, but the masses in play high ...

An increase can occur if, for example, we cultivate land that was cultivated before, for quite a long time: tillage and large removals of biomass (if we harvest significant parts of cultivated plants) can lead to a negative annual balance. Cultivation and plowing could have brought down the humus level.

Grassing can then result in a slow increase in the humus level, i.e. sequestration of C.

Note: the level of humus, under crops, can increase by the simple fact that we leave the roots and certain "falls" in place!
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by Did67 » 17/06/15, 17:41

moinsdewatt wrote:
But have you not already destroyed the preexisting humus in the establishment of this lawn ???
..


It doesn't go away like that, humus!

The mineralization rate (=% of humus which is destroyed in mineral elements per year) varies according to many factors: nature of the soil, climate, work of the soil, humidity ...

It varies from about 0,6 to 0,7 up to 2% (in medium soils; some marshy soils may have lower mineralization; hence often black colors ...

So this is not what we did to install a lawn that will weigh (I am not talking, of course, of backfilling with "inert", deep soils, instead of "topsoil" removed during digging foundations ...)
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