Study: A Regional Analysis of Sweet Potato and Cassava Yield for Ethanol Production
20 August 2008
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| Calculated bioethanol yield per hectare. Click to enlarge. Data: Ziska (2008) |
A study by Agricultural Research Service (ARS) scientists found that sweet potatoes grown in Maryland and Alabama, and tropical cassava grown in Alabama, yielded between two to three times as much carbohydrate (starch, sucrose, glucose) for fuel ethanol production via fermentation as field corn grown in those states.
Dr. Lew Ziska, a plant physiologist at the ARS Crop Systems and Global Change Laboratory in Beltsville, Md., and colleagues at Beltsville and at the ARS National Soil Dynamics Laboratory in Auburn, Ala., performed the study. The research is unique in comparing the root crops to corn, and in growing all three crops simultaneously in two different regions of the country.
Relative to carbohydrate production from corn in each location, sweet potato and cassava yielded approximately 2.8x and 2.9x respectively as much carbohydrate as corn in Alabama; 2.3x and 0.5x respectively for the Maryland site. For sweet potato, overall carbohydrate production was 9.4 and 12.7 Mt Ha-1 for the Alabama and Maryland sites, respectively. For cassava, carbohydrate production in Maryland was poor, yielding only 2.9 Mt Ha-1. However, in Alabama, carbohydrate production from cassava averaged ~10 Mt Ha-1.
Averaged for both locations, sweet potato yielded the highest concentration of root carbohydrate (ca 80%), primarily in the form of starch (ca 50%) and sucrose (ca 30%); whereas cassava had root carbohydrate concentrations of (ca 55%), almost entirely as starch.
Sugarcane, which contains 10-15% sucrose, can produce 8 to 12 Mt of carbohydrate Ha-1; corn contains 60-65% starch and produces between 7 to 10 Mt carbohydrate Ha-1.
Yet, because sucrose is easier to convert to ethanol than starch, actual bioethanol yields are approximately 6.4 to 9.6 and 2.0 to 2.8 m3 Ha-1 for sugarcane and corn, respectively. Assuming a similar conversion efficiency for corn and cassava, cassava grown in Maryland would not be competitive with either corn or sugarcane. For cassava grown in Alabama however, bioethanol yields would be approximately 4.0 m3 Ha-1 which is comparable to corn bioethanol production in this region. Interestingly, because of the greater sucrose yields for sweet potato relative to cassava, bioethanol production would be 5.2 m3 Ha-1 in Alabama (3 and 2.2 m3 Ha-1 from sucrose and starch); and, 6.4 m3 Ha-1 in Maryland (3 and 3.5 m3 Ha-1 from sucrose and starch). For sweet potato, these potential yields of bioethanol are more than double estimates of bioethanol from corn at each location and are approaching the lower limits of sugarcane production.
—Ziska et al. (2008)
The disadvantages to cassava and sweet potato are higher start-up costs due primarily to increased labor at planting and harvesting times. If economical harvesting and processing techniques could be developed, the data suggests that sweet potato in Maryland and sweet potato and cassava in Alabama have greater potential than corn as ethanol sources, according to the researchers.
| Carbohydrate and Calculated Bioethanol Yields | ||
|---|---|---|
| Crop | Carbohydrate yield Mt Ha-1 | Calculated ethanol yield m3 Ha-1 |
| Corn | 7-10 | 2.0-2.8 |
| Sugarcane | 8-12 | 6.4-9.6 |
| Cassava - Alabama | ~10 | 4.0 |
| Cassava - Maryland | 2.9 | na |
| Sweet Potato - Alabama | 9.4 | 5.2 |
| Sweet Potato - Maryland | 12.7 | 6.4 |
Further studies are needed to get data on inputs of fertilizer, water, pesticides and estimates of energy efficiency. Overall, the data indicate it would be worthwhile to start pilot programs to study growing cassava and sweet potato for ethanol, especially on marginal lands.
A separate study by Ziska and colleagues also found that wild kudzu—an aggressive vine species imported from Asia to control soil erosion—stands in Alabama and Georgia could produce 5 to 10 tons of carbohydrate per hectare, which would rival carbohydrate production from corn and sugar cane fields, but without the costs associated with planting, fertilizer and pesticides. This would rival carbohydrate production from corn and sugar cane fields, but without the costs associated with planting, fertilizer and pesticides.
ARS is a scientific research agency within the US Department of Agriculture.
Resources
Lewis H. Ziska, G. Brett Runion, Martha Tomecek, Stephen A. Prior, H. Allen Torbet, and Richard Sicher (2008) A geographical evaluation of root-crops as potential carbohydrate sources for bioethanol production.
So maybe we do not cellulostic ethanol, maybe we just need the right feedstock.
Even if they are harder to plant and harvest, a little work on automation might sort that out.
And keep looking for other crops - perhaps work out a protocol for evaluating new crops so many groups can do it simultaneously and consistently.
Posted by: mahonj | 20 August 2008 at 02:14 PM
Would that mean that fuel would be expensive during the early spring and cheap in the late fall? Is it possible to get multiple crops per year in the south US? I eat Yams and sweet potato all the time, so I'd hate to see the prices sky rocket.
Posted by: | 20 August 2008 at 02:59 PM
Root base feedstock is not the right approach for biofuel production, they tried in France with sweet beat it doesn't make sense economicaly, intense labor, high energy input, require a lot of tilling, generates strong erosion of soils.
non perenial crops is the only acceptable feedstock for biofuel : period.
Posted by: Treehugger | 20 August 2008 at 04:48 PM
When get 10 pound gummi bears to grow on trees, we will be set.
Seriously, I think biofuels will have a place in the mix, but other renewables will soon surpass them -- specifically electric producing sources. But then, who knows.
Posted by: JMartin | 20 August 2008 at 06:35 PM
Potato contains too much moisture, so it is subject to rotting; it is expensive to transport and to store. Dry corn is much more convenient.
Posted by: Andrey Levin | 20 August 2008 at 09:54 PM
There was a news story where they walked through a corn field to show how good the crop was, even with the recent flooding. Looking at the 6 foot tall stalks, I could not help thinking how much biomass is there. Corn for food and stalks for fuel.
Posted by: sjc | 21 August 2008 at 10:55 AM
10 / 2.9casava.
9.4 /2.7potatoe.
Different outputs from different states?
Obviously these outputs reflect growing conditions include soils temps and water.
The point is that as in all agriculture there will be as much or more seasonal variation.
This means that availability and cost will vary immensely making both the refinery plant and Hectare planting sizing will be up and down by 30% (we are always conservative here).
As with the unreliable corn supply, leading to wild economic fluctuations.
All food crops affect the price of food for human consumption even when fed through intermediate livestock.
Basically all agricultural lands are better used or held back and rested for (International) food security
until the world population and projected growth is stabilised.
Hint - Its all well and good getting a warm and fuzzy feeling encouraging population increases , when it comes to seeing those populations live well within in a sustainable ecosystem, that also needs recognition.
Posted by: arnold | 21 August 2008 at 05:31 PM
As said, even with the best producing plants, there is not enough land area to grow enough fuel to supply a large part of the US energy use. It won't even supply a large part of the liquid fuels used for transportation.
Plug in hybrid cars are a better investment of money and resources.
Every life form, including humans, has forever ingested and retained radio-active postassium in order to live. Humans have always been radio-active and cannot afford to live if they avoid radio-activity as much as possible. Radio-activity does not only come from humans it comes from the earth and space and cannot be avoided.
Life forms, two billion years ago, had existed with more than twice as much built in radio-activity than we do now, so we know that we can and many people have demonstrated that we can live with more than twice the radio-activity by living at high altitudes.
Nuclear power plants can provide electricity to plug-in-hybrid cars and heat to ethanol plants to eliminate the use of fossil fuels or even bio-mass for that purpose. Eventually they can produce cheap hydrogen for making fuels. ..HG..
Posted by: Henry Gibson | 23 August 2008 at 02:38 PM
You do not need more land if you use the corn stalks from the corn you already grow. There are more than 100 million acres in corn production. Even with only 2 tons per acre, that is 200 million tons at 100 gallons per acres for 20 billion gallons of alcohols. That is more than E10 from cellulose and that is just corn stalks. You also have wheat straw, rice straw, forest product waste totaling one billion tons of biomass each year for 100 billion gallons of the 140 billion we use. NO extra land, just use the biomass left over from what we grow now. Combine that with using it in E85 hybrids that get 40 mpg, and you eliminate oil imports all together.
Posted by: sjc | 23 August 2008 at 04:13 PM
Don't you need some of that biomass to go back into the soil, to replenish it?
Posted by: danm | 24 August 2008 at 05:57 AM
sjc:
There is an old Chinese saying that says that whatever is removed from th soil has to be returned in one form or another.
Using plants to produce all the liquid fuel we use (need) may be too demanding from most soils.
It may be wiser to first reduce our liquid fuel consumption by 75% with widespread use of PHEVs and BEVs before attempting to do the impossible and/or permanent damage to the soil required for food production.
Getting rid of our GHG producing gas guzzlers is the first step.
Posted by: HarveyD | 24 August 2008 at 09:56 AM
BioChar from the gasification process returns nutrients to the soil. You can also make nitrogen fertilizer from the NH3 that get from the biomass. Making it a series operation where you have to get some percentage of PHEVs will waste time. Do a parallel effort where we work on FFV PHEVs AND biomass gasification on a large scale. That way we get their faster.
Certainly you have to consider soil nutrients, only a fool would not. But after all that is considered, we need to get on with it in a BIG way over the next 10 years. The USDA and DOE can work out the detail with the farmers. But we will need MUCH more than the token steps that have been taken and we will need them starting next year non stop for the next 10 years...at least.
Posted by: sjc | 24 August 2008 at 10:07 AM
The answer to our energy crisis does not lie with one crop or one source of energy. A problem that large requires multiple solutions, and I think that ethanol is one of the most important and most effective solutions we have at our disposal.
Posted by: Bryan | 24 August 2008 at 12:46 PM
It's important to match the technology with the region. Biofuels and bioenergy makes more sense for low to medium population density regions. Nuclear energy makes sense for high population density regions.
When Craig Venter invents a prolific micro-organism that makes gasoline, diesel, and jet fuel, the equation will change, but who knows when that will be?
Fossil fuels will be used for the next century at least for transportation (jets, ships, heavy equipment, locomotives etc) needs--heavy oils, shale oils, oil sands, coal to liquids, gas to liquids, etc. Gasification and F-T works quite well with solid FF's too at current oil prices.
Solar and wind suffer from intermittency, and are still very expensive for all that.
Once you grow up and realise that Al Gore's been getting rich off of your gullibility, the future becomes a lot clearer and less fearful.
Posted by: Al Fin | 24 August 2008 at 05:21 PM
We are a renewable fuels' consulting company based in Buffalo, NY. We represent a Brazilian company that has developed an extraordinary biotechnology for producing ethanol out of Sweet Potato, BIOEX Etanol.
We are currently looking for investors, cooperatives, partners or parties interested in a joint venture for building ethanol plants based on the referred genetic matrix.
The technology we represent has proven to provide outstanding results as for productivity and quality in all aspects.
Please, check out our website and feel free to reply or contact our main office in Buffalo, NY for more information. www.churchsinternational.com
Kind Regards
Posted by: Renato | 23 September 2008 at 01:06 PM
We are a renewable fuels' consulting company based in Buffalo, NY. We represent a Brazilian company that has developed an extraordinary biotechnology for producing ethanol out of Sweet Potato, BIOEX Etanol.
We are currently looking for investors, cooperatives, partners or parties interested in a joint venture for building ethanol plants based on the referred genetic matrix.
The technology we represent has proven to provide outstanding results as for productivity and quality in all aspects.
Please, check out our website and feel free to reply or contact our main office in Buffalo, NY for more information. www.churchsinternational.com
Kind Regards
Posted by: Renato | 23 September 2008 at 01:10 PM