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Tutorial 2

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Biological Sciences
Rudy Boonstra

TUTORIAL 2 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. GROUP #5 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 14:65-76. Your questions: 1. The authors state, at the bottom of p.68, that Also 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? Both. Is this a fact? What does it say about soybean? It doesnt deplete the soil? It uptakes nitrogen right? BGYC58H3F.October,4,2007 TUTORIAL 2 1 www.notesolution.comCorn 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 litre. 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 by-product. 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 kcalyear mg input per hectare (you get 10 tons more per hectare so more energy per yield). Corn requires 8.1 million kcalyear mg input per hectare. Corn can be used as food and switch grass cannot. Answer Question #1: How do you interpret this statement? BGYC58H3F.October,4,2007 TUTORIAL 2 2
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