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energy required to cut an acre of grass ?
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sadeik



Joined: 29 Apr 2010
Posts: 11

PostPosted: Fri Apr 30, 10 5:59 pm    Post subject: Reply with quote
    

sadeik wrote:
Yes I was trying to beat him, I gave William a meaty 50cc clearing saw with a grass cutting blade needless to say he won but I'm going to beat him this year cos I'll put some dodgy fuel in


I have been working out how much energy it takes to cut an acre of grass by scythe. Apparently humans at work have an output of 100w (that is to say each one of us could only produce enough energy to light an old 100w light bulb, 2 or three if they are energy efficient kind)
Now if on average a man cuts one acre in ten hours for example then we get a figure of one kilowatt/hour (thats only 13p in electricity prices for a days work shocking)

sadeik



Joined: 29 Apr 2010
Posts: 11

PostPosted: Sun May 02, 10 2:27 pm    Post subject: Reply with quote
    

Does anybody know how many acres of grass a horse can cut in a day with an old horse drawn finger bar mower. I know that one horse will provide 750 watts of energy so assuming that if a man can cut one acre for 100 watts of energy then a horse should cut 7.5 acres but i would like to know if this is right or not

simon

sadeik



Joined: 29 Apr 2010
Posts: 11

PostPosted: Mon May 03, 10 4:26 pm    Post subject: Reply with quote
    

gil wrote:
I can split this post out into a separate topic under Land Management if you like - you might get more folk looking at it [not just those in the east] - yes ?


Not a bad idea, took a while to find but its about 45 minutes to one hour for one horse to cut an acre with a horse drawn finger bar mower but that was in a competition so I guess that'll be the same as a scything competition and no way I could cut all day long at competition speed.
Just looked at the time it would take me to cut an acre at competition speed 3 hours so I'll double it. That'll be 600 watts to a horse which I'll double and that will be 1500 watts so I guess human power could be more efficient with energy.
Therefore everyone should cut their own grass and eat horses

gil
Downsizer Moderator


Joined: 08 Jun 2005
Posts: 18398

PostPosted: Mon May 03, 10 6:40 pm    Post subject: Reply with quote
    

We need Nat S on the thread to discuss where draft oxen fit into this.

Penny Outskirts



Joined: 18 Sep 2005
Posts: 23385
Location: Planet, not on the....
PostPosted: Mon May 03, 10 6:56 pm    Post subject: Reply with quote
    

sadeik wrote:
Therefore everyone should cut their own grass and eat horses



Ronnie



Joined: 11 Jun 2009
Posts: 73
Location: Highlands
PostPosted: Mon May 03, 10 7:49 pm    Post subject: Reply with quote
    

Sorry, I don't have anything to add to your numbers. But this kind of exercise does show how well and truly f*cked we're all going to be once the oil runs out...

Kunstler said that each of us has the equivalent of 100 oil slaves working for us 24/7/365 to support us in the manner to which we have become accustomed.

Oh, and each calorie of food we grow has had 10 calories of oil used to produce it...

Bulgarianlily



Joined: 01 Jun 2008
Posts: 1667
Location: South West Mountains of Bulgaria
PostPosted: Tue May 04, 10 5:51 am    Post subject: Reply with quote
    

Ronnie wrote:


Oh, and each calorie of food we grow has had 10 calories of oil used to produce it...


Is that an averaged out figure? For whom does this apply? I am pretty sure that here that is not the case, as there is only one tractor and most people don't use it, yet they produce the majority of their food. I am sure it does apply to bread, as that is produced from flour from larger farms and there is some food miles involved. I can't believe that is the figure for the entire world population. Any links to a reference?

Edited to add, I found this which seems an excellent article on the subject. https://www.harpers.org/archive/2004/02/0079915

I quote "Every single calorie we eat is backed by at least a calorie of oil, more like ten. In 1940 the average farm in the United States produced 2.3 calories of food energy for every calorie of fossil energy it used. By 1974 (the last year in which anyone looked closely at this issue), that ratio was 1:1. And this understates the problem, because at the same time that there is more oil in our food there is less oil in our oil. A couple of generations ago we spent a lot less energy drilling, pumping, and distributing than we do now. In the 1940s we got about 100 barrels of oil back for every barrel of oil we spent getting it. Today each barrel invested in the process returns only ten, a calculation that no doubt fails to include the fuel burned by the Hummers and Blackhawks we use to maintain access to the oil in Iraq.

David Pimentel, an expert on food and energy at Cornell University, has estimated that if all of the world ate the way the United States eats, humanity would exhaust all known global fossil-fuel reserves in just over seven years. Pimentel has his detractors. Some have accused him of being off on other calculations by as much as 30 percent. Fine. Make it ten years."

It looks like the oil to food ratio applies to the US and other highly developed nations. Makes you wonder what would have happened if the 'green revolution' which made three times the wheat grow than before, hadn't happened. Maybe the world's population would have stabalised before now (at a terrible short term cost in human life, but that is going to happen at some point, I guess). Time to sharpen up the hand scythes.

vegplot



Joined: 19 Apr 2007
Posts: 21300
Location: Bethesda, Gwynedd
PostPosted: Tue May 04, 10 7:32 am    Post subject: Reply with quote
    

The sums don't factor in the time component. It might be more energy efficient to mow by hand. When you need to produce as much as possible in the shortest time, due to constraints such as the weather then time becomes an important factor which puts a different complexion on the equations and their results.

OP



Joined: 28 Jul 2006
Posts: 4661
Location: Yorkshire
PostPosted: Tue May 04, 10 8:16 am    Post subject: Reply with quote
    

I would also hesitate to draw the conclusion that when the oil runs out we will all be back to ploughing with oxen. Oil has replaced older forms of energy, and it is likely that newer forms of energy will be found, well, I hope so! The point made by Bulgarianlilly about the green revolution is a good one.

Mrs R



Joined: 15 Aug 2008
Posts: 7202

PostPosted: Tue May 04, 10 8:25 am    Post subject: Reply with quote
    

Hey I'm back to ploughing with oxen already it's not so much lack of oil that is my deciding factor, more the cost of it. These new sources of power haven't made it to Rosewood yet and I'm sceptical as to whether we'd be able to afford them anyway.

cab



Joined: 01 Nov 2004
Posts: 32429

PostPosted: Tue May 04, 10 8:55 am    Post subject: Reply with quote
    

If I had an acre of grass, I'd probably get sheep. It would seem foolish to cut it with a mower.

I despair of the obsession our society seems to have with manicured lawns. Almost as much as I despair of the dire condition of my own lawn...

vegplot



Joined: 19 Apr 2007
Posts: 21300
Location: Bethesda, Gwynedd
PostPosted: Tue May 04, 10 9:12 am    Post subject: Reply with quote
    

cab wrote:
If I had an acre of grass, I'd probably get sheep. It would seem foolish to cut it with a mower.

I despair of the obsession our society seems to have with manicured lawns. Almost as much as I despair of the dire condition of my own lawn...


I had assumed this was for the production of hay rather than just cutting grass but it is an assumption.

Rob R



Joined: 28 Oct 2004
Posts: 31902
Location: York
PostPosted: Tue May 04, 10 9:21 am    Post subject: Reply with quote
    

cab wrote:
I despair of the obsession our society seems to have with manicured lawns. Almost as much as I despair of the dire condition of my own lawn...


My dad lives next door to someone who is obsessional about their lawn- trimmed to perfection it is, right next to his which has such a good stand of grass on that I'd like to strip graze it with the cattle.

Rob R



Joined: 28 Oct 2004
Posts: 31902
Location: York
PostPosted: Tue May 04, 10 9:23 am    Post subject: Reply with quote
    

vegplot wrote:
cab wrote:
If I had an acre of grass, I'd probably get sheep. It would seem foolish to cut it with a mower.

I despair of the obsession our society seems to have with manicured lawns. Almost as much as I despair of the dire condition of my own lawn...


I had assumed this was for the production of hay rather than just cutting grass but it is an assumption.


That wouldn't exclude you from getting sheep though, as even hay has to be fed to something...

and self-harvesting in a managed grazing system is one of the major advantages of pasture farming.

sadeik



Joined: 29 Apr 2010
Posts: 11

PostPosted: Tue May 04, 10 2:58 pm    Post subject: Reply with quote
    

Graze sheep all the time on a pasture and eventually you'll get a worm/parasite problem, give it a break for a year by mowing for hay (scythe horse or tractor) and you break the worm/parasite cycle.
Anyway what's wrong with a cow that'll give you milk (cheese etc) and veal!
Having been in Romania they don't have sheep so much in their homestead fields (these graze the open fields and mountain/heath ground with them) Instead they mow by hand and the whole family takes part in this affair, the hay is kept for the cows which mostly stay inside but sometimes go up the mountains to graze. They might not realise that they are keeping a clean grazing system but thats what they are doing. Another thing is the field is not trampled you get two cuts of hay and more milk as the cow does not waste energy walking about except when they go into the mountains.
One other very important advantage is the people are very fit and the young ladies are well toned and tanned, perhaps models should have a go at hay making!

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