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Tutorial 2

Biological Sciences
Course Code
Rudy Boonstra

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October 4, 2007
It is very important that you do the readings before you come to class. I will be putting you into
groups so that you can answer some questions. I know it is hard to have discussions with a class
this large. After doing your readings I would like you to come up with a question and answer.
In future sessions if there are not a lot of volunteers I will pick a name from the list and you will
be expected to have your question to give to the class and also have your answer.
I will hand out papers and you will form your groups. Each group has to have a spokesperson
that I will call on when needed.
One group has 2 easy answers. When you are finished send someone from your group up to tell
me when you are done. If people have questions it is easiest to send someone from your group to
ask me.
Your paper: Pimental, D. and T.W. Patzek. 2005. Ethanol production using corn, switch
grass, and sod biodiesel production using soybean and sunflower. Natural Resources Research
Your questions:
1.The author’s state, at the bottom of p.68, thatAlso note that these energy credits are
contrived because no one would actually produce livestock feed from ethanol at great
costs in fossil energy and soil depletion (Patzek, 2004).” How do you interpret this
statement, and what do you think of it?
2.How do you think corn and switch grass compare as potential ethanol sources? In
particular, what ecological effects do you think would be associated with large scale
adoption of corn or switch grass as the major source of ethanol?
Your answers:
Are they talking about ethanol from corn or soybean?
Is this a fact?
What does it say about soybean? It doesn’t deplete the soil?
It uptakes nitrogen right?
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Corn really depletes the soil.
Question #2 - Answer
It says that switch grass is 50%. So corn is better. Should we make a table?
So it is negative 50% for switch grass. The summary says 50% more than the actual ethanol that
is produced and the corn is 29%. So the corn is better. It makes less fossil fuel. The cost is 54
cents instead of 45 cents.
In terms of energy output corn is 29% so it takes 29% more fossil energy than ethanol
fuel produced.
Switch grass takes 50%.
Corn costs 45 cents to produce 1 litre vs. and switch grass costs 54 cents to produce 1
Corn is better in this case.
They are invading the energy balance. They put it into the calculation and that is why it is
inflated. You get 29% less than you get from the actual ethanol. You can use it but nobody
does. So it is actually 20% but they are inflating it.
How do you interpret the statement? So really we are using more energy. This is the byproduct
of creating it.
So they are saying that we are using more energy than they are saying if they produce this. The
If they take the corn left over and make livestock feed then minus that.
How do we interpret this statement? What do you think of it?
Takes 20 to 30%.
You have to compare which is better ecologically. Mention the waste for corn?
There is competition for land. This is for the second question.
Corn produces 13 litres of waste to produce 1 litre of ethanol.
Switch grass uses half as much herbicide than corn. Corn also uses insecticides and
switch grass does not.
You can produce more switch grass on the land than you can corn.
Switch grass - 3.8 million kcal/year mg input per hectare (you get 10 tons more per
hectare so more energy per yield).
Corn requires 8.1 million kcal/year mg input per hectare.
Corn can be used as food and switch grass cannot.
Answer Question #1:
How do you interpret this statement?
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It isn’t factual. This is the author’s opinion. So we can say because it is just an opinion.
We don’t know if people actually produce livestock feed. By product of producing corn.
There is a reference which means it is true.
Class Discussion:
The National Geographic article gives an introduction to many of the issues. I thought it was
more balanced than some of the scientific literature that we looked at.
Define the NEB Ratio? Neb is net energy balance which is energy output subtracted by energy
input. We look at energy yielded from fuel vs. energy ingested into the production for example
of ethanol. Ratio is some cases for ethanol where it yields 25% more than in its production and
that is the NEB.
NEB ratio is done a little differently. It is the output of energy vs. input of energy. It is one
thing to remember…terminology NEB and NEB ratio. Ratio is output divided by input so think
of it for ethanol it is 25% more out than what you would put in to get that.
Group #2:
What is the significance of NEB ratio less than 1?
Put more energy input than we get output. If the output from a biofuel is less than input your
NEB ratio will be less than 1. So you are putting more into the production than what you are
getting out.
What is the significance of that? If you saw an NEB ratio of less than 1?
It is costing you more to produce and overall it costs more. It is not necessarily going to be bad
in all cases if some of your inputs are not non-renewable fossil inputs. There is nothing that says
that if I want to drive from point A to o=point B that I have to do it with a fuel that has a ration
greater than 1. If I am relying on fossil fuel totally it means I have to get more fossil fuel out of
the earth and I burn and that is impossible, I can’t just say that. If you have another source of
energy for your inputs there is nothing inherently wrong with driving an ethanol car where it
took more energy than what you are burning.
Question #1 – part 2:
Neb ratio takes into effect everything involved in the production. Facility level all energy used
(including energy for employees to run the plant, etc.) the ratio is too generalized. When
comparing fossil fuels used in this ratio vs. renewable resources we could get a similar NEB ratio
if we use the same energy from coal as from solar. Solar energy is renewable so it makes no
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