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U.S. corn yields to double in the next 20 years?

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This past month I spoke at the Bryant-Lake Bowl as part of the Bell Museum of Natural History's Café Scientifique series. I had been asked to address the question, "Can agriculture deliver food, fuel, and fiber?" My answer is that it already does and that there's every reason to expect it will continue doing so in the future, even as the world's population grows and becomes increasingly affluent. There are limits, of course, to what can be expected, especially as we look to offset greater amounts of our fossil fuel use with bioenergy. What's more, we run the real risk of incurring tremendous environmental and social costs if when asking more of our land we also neglect to treat it in a more sustainable manner.

In my talk I focused largely on the case study of corn ethanol, which has been at the center of my recent research. I described many of its benefits and drawbacks, summarizing what my colleagues and I have learned these past few years as we investigated whether ethanol really is a better transportation fuel alternative than gasoline (PDF).

Central to any assessment of ethanol's sustainability is the question of how quickly corn yields increase. This is especially important given the rapid growth of this industry. A decade ago we converted about 5% of the corn we grew in this nation into ethanol, while today it is over 30% (PDF). Achieving higher yields from each acre we farm means less cropland is needed to produce the same amount of grain. This in turn lessens the potential need for other land to be brought into corn production, be it planted to other crops, in agricultural reserve programs, or in native ecosystems never before cultivated.

Of course, while higher yields reduce the land footprint of agriculture, they can also result in greater environmental damage, such as from the increased use of fertilizers and irrigation. Tradeoffs such as these are best understood within the context of life cycle assessment, which is a method of quantifying the various environmental impacts a given product.

Let's return to the question of how quickly corn yields increase, which will be the focus of this blog entry. I recently heard a representative of the National Corn Growers Association state the following:

"We have increased our corn production. We've doubled it in the last 40 years, and we're on track to double it again in the next 20 years."

Let's look at what the data show. The first half of this statement is correct. In the last 40 years, U.S. average corn yields have risen from approximately 75 bushels per acre to 150. The second half, however, is not supported by the data. If current trends are followed, corn yields will increase by about 50 more bushels per acre over the next 20 years, or a 33% increase. For corn yields to double (i.e., a 100% increase), the average annual increase in yield would have to more than triple from 1.9 bushels more per acre to 7.5. Indeed, the USDA itself forecasts a 2.0 bushel per acre per year increase (See Table 8 in this document (PDF).)

U.S. average corn yields
hill2010.jpg

To help put this in perspective, doubling the current average yield from 150 bushels per acre to 300 by 2030 would mean the average yield would be where the 2009 National Corn Yield Contest winners (PDF) are today. It is also worth noting that 300 bushels per acre is where the average irrigated contest winners for Nebraska has remained for the past 25 years, suggesting that this may be, in the words of Prof. Ken Cassman and colleagues at University of Nebraska - Lincoln, the "yield potential ceiling" for corn in the North-Central U.S.

Nebraska average corn yields (From Cassman et al. 2003)
cassmanetal2003.jpg

It is of course possible that the representative of the National Corn Growers Association simply misspoke, but this was not the first nor the only time I have heard this claim from the corn and ethanol industries. For example, in an article entitled "Agriculture: Will the yield keep growing" published in the Minneapolis Star Tribune on June 3, 2009, I saw the following:

'"We are projected to double corn yields in this nation in the next 20 years," said Jeff Broin, CEO of ethanol refiner Poet, a South Dakota-based company that produces 1 billion gallons of ethanol a year.'

I have been wondering why a forecast so poorly supported by the data has been so widely repeated, so I did a little sleuthing. The best I can tell is that this traces back to a claim made by Monsanto as reported in a press release dated June 4, 2008. Entitled "Monsanto Will Undertake Three-Point Commitment to Double Yield in Three Major Crops, Make More Efficient Use of Natural Resources and Improve Farmer Lives", it contains two important pieces of information relevant to this discussion. First, it states that "Monsanto will double yield in its three core crops of corn, soybeans and cotton by 2030, compared to a base year of 2000." The projected doubling period, therefore, is 30 years -- 50% longer than the 20 year timeframe. Second, the average reported is not simply a U.S. average, but that of the U.S., Brazil, and Argentina:

"This would mean, for example, that corn production in the prominent agricultural markets of Argentina, Brazil and the United States would reach a weighted average of 220 bushels per acre by 2030, compared to 109.1 bushels per acre in 2000."

I'll crunch the underlying numbers and present them in a future blog entry. They necessarily imply an acceleration in corn yields over what I have presented above. I'll also present more data on why there is no a priori reason to expect this to be so, even with such exciting events as the recent sequencing of the corn genome and 2009 having highest average U.S. corn yield to date. Regardless, it's evident from this press release that the claim of doubling U.S. corn yields over the next twenty years exceeds the expectations even of Monsanto.

(Last year was a bumper harvest, no doubt, but there is no reason to believe it represents the beginning of an accelerated annual yield increase given past annual variability. It's also interesting to note that a quick glance at the figure I presented above shows that 1 in every 3 (15 of 45) of the past 45 years have been record corn yields!)

Update (1/20/10): I have been made aware of the following article, which includes a statement on yield doubling in the next twenty years made by a second NCGA executive.

  The opinions expressed in this blog are those of the author(s) and not necessarily
  of the Institute on the Environment/University of Minnesota.

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