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Saturday, December 12, 2009

GAO Report: Ethanol Has High Water Cost, Especially in South Dakota

I've written previously that, among other things, increasing corn ethanol production may drain water supplies and be harm water quality. The General Accounting Office has issued a new report that supports the idea that, even if ethanol is a good domestic alternative to foreign fossil fuel, we need to consider the other resources we'll pour into the ground to get it.

The report notes that South Dakota is part of a twelve-state region that produced 89% of America's corn in 2007 and 2008 and 95% of the corn ethanol in 2007. The states in USDA Region 7 (that's us, along with North Dakota, Nebraska, and Kansas) rely heavily on irrigation to get corn to grow. In our neck of the woods, growing one bushel of corn requires 865 gallons of irrigated water. In the other big corn-producing states (the rest of the Midwest, from Minnesota and Iowa over to Michigan and Ohio), it rains enough that the same bushel of corn requires only 19 to 38 gallons of irrigation.

Given an average yield in 2008 of 153.8 bushels per acre, another section of grassland turned to corn grown with irrigation will consume another 88 million gallons of water. That's as much water as South Dakotans consume for domestic use every eleven days. And that's a single section turned to corn. Look bigger: South Dakota's ethanol refineries use 291 million bushels of corn each year. That corn took a staggering 252 billion gallons of water to grow, almost 90 years worth of South Dakota domestic water consumption.

Ninety years of domestic water supply, traded for one year of ethanol production. How long can we sustain that trade-off?

p.s.: U.S. Farm Service data suggest that between 2002 and 2007, 475,000 acres of grassland in North and South Dakota were newly plowed for crop production.


  1. Apparently nearly 5 million acres of corn were planted in SD. I was unable to find any breakout of irrigated and non-irrigated corn however. I suspect the irrigated acreage is a relatively low percentage of the total acres however.

    I guessed that irrigated and dryland data for SD would turn up easily in Google, but was surprised at the lack of such information. All kinds of propaganda for corn acreage, but statistics either non-existent or not obvious.

  2. Here's another case of lousy, incomplete AP journalism where separate facts are thrown at the wall and magically weaved into a "story". Little corn in SD is irrigated. Even without ethanol, it would be grown anyway - as it has for generations. SD's average yield in 2008 was about 130 bushels. Of the 291 million bushels (US) refined by ethanol plants, over one third of that, 100 million bushels, is then recycled as livestock feed (distillers grains), and some syrup also re-enters the feed cycle. Remember that little of SD's corn is food - it's feed. Huge difference. The valid concern of over-cropping the semi-arid western plains has been a concern since the 1930s; concerns over aquifer depletion are also that old. Yields and cropping will soon plateau corn ethanol production around 15 billion gallons per year. That's why the renewable fuel standards incentivize cellulose ethanol. Blaming the borrowing of corn starches for ethanol production for water abuse is misleading and misinformation - at best.
    John Kelley

  3. Actually, John, I'm not seeing the misinformation. Replacing grassland with corn planting means more water and resource use. The GAO's report makes the point that getting to cellulosic switchgrass ethanol will mean less water usage, since you don't irrigate switchgrass.

    Forget the hacks at AP: let's read the GAO report itself:

    "However, the impact of corn cultivation on water supplies in these regions varies considerably. For example, in USDA Region 7, which comprises North Dakota, South Dakota, Kansas, and Nebraska, the production of one bushel of corn consumes an average of 865 gallons of freshwater from irrigation. In contrast, in USDA Regions 5 and 6, which comprise Iowa, Illinois, Indiana, Ohio, Missouri, Minnesota, Wisconsin, and Michigan, corn is mostly rainfed and only requires on average 19 to 38 gallons of supplemental irrigation water per bushel."

    That text seems to say pretty clearly that all corn grown in our region, on average, uses a lot more water than the corn grown in Regions 5 & 6.

    Now John, you may have a point about the realtive amount of irrigation in South Dakota. This Ag Census data from the USDA finds SD irrigating 374K acres in 2007, down from 401K in 2002. ND only irrigated 236K acres in 2007, but NE irrigated 8.56M and Kansas 2.76M.

    That same USDA data says in 2008, corn was harvested from 176,000 irrigated acres on 669 farms in South Dakota. Corn was harvested from 302,000 non-irrigated acres on 605 farms. (Douglas! Double check, make sure I read that data right!)

    Now John, if I've done my math right, you tell me if 37% of our corn acreage -- 304 million bushels, over 40% of our production -- is "little corn".

    Sure, we've been growing corn for a long time. But corn is more resource instensive than other crops. And pressure to keep planting corn for ethanol reduces crop rotation, and less crop rotation means more depleted soil and more soil erosion. What if we switched to other crops? Would we get as much food (people food!) without using as much irrigation or fertilizer or pesticides? Would we see less lower nutrient load from run-off into our streams and lakes?

  4. Cory, you have more patience or luck than I had finding information. What is in the table you found appears to be as you reported on irrigated corn acreage in SD.

    Whatever it was that I found did not have numbers remotely like those.

    Nebraska's center pivots are draining the antique water from the Ogalla (sp?) acquifer. Not sure what irrigation in SD damages however.

    I am still not sure the high number for water used for corn irrigation is correct however. The data available seems to make sense of these numbers more difficult than necessary.

  5. Patience and luck -- don't leave your homepage without 'em! :-)

    Some of the water use numbers seem staggeringly high to me, too -- I'm wondering if some USDA guy will look up from his slide rule and say, "Whoops! Missed a decimal point!" But until then, I'll stick by these numbers... and remind folks that corn ethanol uses a whole lot of water.


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