Dennis Avery, et al.
These letters appeared in Science, Vol 307, Issue 5714, 1410-1411, March 2005
In his review of Mendel in the Kitchen: A Scientist’s View of Genetically Modified Foods by N. Fedoroff and N. M. Brown (“Changing genes to feed the world,” Books et al., 29 Oct. 2004, p. 815), D. Pimentel misrepresents the impacts of genetically modified herbicide- tolerant (HT) crops and the consequences of organic farming, which he offers as a more sustainable way to meet the food challenges of the 21st century.
Pimentel derides HT crops because they result in increased herbicide use and potential pollution, yet are not significantly more effective against weeds than herbicides and tillage combined. This completely overlooks the drastically reduced soil erosion, increased soil organic matter, and reduced fossil fuel consumption made possible by herbicides and HT biotech crops. The Soil and Water Conservation Society says that herbicide-based, low- and no-tillage cropping systems are the most sustainable ever (1), points made in the book.
Pimentel further denies the benefits of HT crops when he claims that “the soil has to be tilled” with current annual grain crops, causing “serious soil erosion.” Perversely, Pimentel uses this misrepresentation to promote organic farming, which relies heavily on erosion-causing tillage for its weed control.
Pimentel selectively cites Rodale Institute research to claim that organic crop yields are equivalent to nonorganic. Yet, many long-term studies have shown a 10 to 40% organic yield deficit (2-4).
Pimentel may be correct in claiming “organic approaches would reduce the use of fossil energy in corn production by about 30 percent” due to not using synthetic fertilizer, but as Fedoroff and Brown note, only by using far more land per ton of food produced. Replacing synthetic nitrogen fertilizer would require at least a fourfold increase in manure applications or equivalent green manure crops (5).
Humanity already farms more than one-third of Earth’s total land area, and additional land cleared for organic fertility and yield deficits would be of lower productivity, greater erosion potential, and higher ecological sensitivity. As Fedoroff and Brown make clear, genetic engineering offers us powerful and important tools to sustainably feed the larger and more affluent global population without using more land and wasting resources.
Alex A. Avery
Hudson Institute
Center for Global Food Issues
Post Office Box 202
Churchville, VA 24421
USA.
C. S. Prakash
Center for Plant Biotechnology Research
Tuskegee University
Tuskegee, AL 36088
USA.
Alan McHughen
Botany and Plant Sciences
University of California, Riverside
Riverside, CA 92521
USA.
Anthony R. Trewavas
Institute of Cell and Molecular Biology
University of Edinburgh
Darwin Building
Edinburgh EH9 3JR, Scotland
UK.
Thomas R. DeGregori
Department of Economics
University of Houston
Houston, TX 77204-5019
USA.
References
1. Soil and Water Conservation Society, Farming for a Better Environment (Soil and Water Conservation Society, Ankeny, IA, 1995).
2. J. Smolik, T. Dobbs, J. Sust. Agric. 9, 63 (1996).
3. M. Shepard et al., An Assessment of the Environmental Impacts of Organic Farming: A review for Defra-funded Project OF0405 (U.K. Department for Environment, Food, and Rural Affairs, London, UK, 2003) (available at www.defra.gov.uk/science/project_data/DocumentLibrary/OF0405/OF0405_909_TRP.doc)
4. P. Mader et al., Science 296, 1694 (2002).
5. V. Smil, personal communication.
________________________________________
Response
Avery et al. incorrectly equate herbicide tolerance (HT) in crops with the no-till cultivation system. No-till may or may not be used with HT. For example, 75% of U.S. soybean plantings include HT, but only 30% of them are planted with no-till (1). No-till conserves soil and water resources, but HT itself does not conserve soil or increase soil organic matter. In fact, HT with clean culture (using an herbicide or other treatments to eliminate all weeds and leave only the crop growing cleanly without competition from weeds) significantly increases soil erosion. HT in crops increases the application of herbicides, and herbicides are the most serious pesticide pollutants in streams and groundwater in the United States (2). Ninety-five percent of corn production acreage in Iowa receives herbicides, and 70% of this land is also cultivated for weed control (3). Soil erosion is a serious problem in the United States. Agricultural soil is being lost about 10 times faster than soil reformation and sustainability (4).
In reviewing the book, I was surprised that Federoff and Brown devoted such a large portion of it to attacking organic agriculture, when organic agriculture has little or nothing to do with plant breeding and genetic engineering. Because of this intense and misleading attack, I felt that I should present the results of the 22-year corn-soybean example of the Rodale Institute in which corn and soybean yields equaled those of conventional corn and soybean production. I agree that not all organic culture of crops produces yields the same as those of conventional crop cultivation (5).
Avery et al. imply that I reported that all U.S. and world agriculture could be grown organically without commercial nitrogen fertilizer. They are incorrect—I never said this in my review, nor have I ever said this in any of the more than 500 scientific papers that I have published.
Worldwide crops are cultivated on 11% of the world’s land area, not 33% as Avery et al. report. Yes, the world has a severe food shortage problem; the World Health Organization recently reported that 3.7 billion people are malnourished. This is the largest number of malnourished people in history. Certainly, we need sound genetic engineering, as well as soil and water conservation, to increase the yields of our food crops and make agriculture ecologically and economically sustainable.
David Pimentel
College of Agriculture and Life Sciences
Cornell University
Ithaca, NY 14853-0901
USA.
References
1. Economic Research Service, U.S. Department of Agriculture, Agricultural Chemicals and Production Technology: Questions and Answers, available at www.ers.usda.gov/Briefing/AgChemicals/.
2. U.S. Geological Survey, Fact Sheet 181-97, June 1998.
3. “Cultivation: An Effective Weed Management Tool,” available at www.extension.iastate.edu/Publications/PM1623.pdf.
4. National Academies of Science, Frontiers in Agricultural Research: Food, Health, Environment, and Communities (National Academies Press, Washington, DC, 2003).
5. D. Pimentel, G. Berardi, S. Fast, J. Agric. Ecosyst. Environ. 9, 359 (1983).
Response to Pimentel response which was not published in Science:
Dr. David Pimentel’s response to our letter in Science (2005, vol. 307:1410-1411) misconstrues some of our points and is simply wrong in other areas.
First, Pimentel incorrectly claims that we equated herbicide tolerant crops (HT) with no-till cultivation systems. We clearly stated that HT crops facilitate both low- and no-till cropping systems, not just no-till. Low-tillage cropping encompasses a large spectrum of conservation tillage cropping, all of which significantly lower soil erosion compared to organic agriculture’s inherent heavy reliance on tillage for weed control.
The inaccurate focus on only no-till cropping results in a major underestimate of the beneficial impacts of HT crops, as demonstrated when Pimentel incorrectly states that “75% of U.S. soybean plantings include HT, but only 30% of them are planted with no-till.”
According to Dan Towery, just-retired director of the Conservation Technology Information Center located at Purdue University and funded by the USDA’s Natural Resources Conservation Service, fully 85% of U.S. soybean acres were planted to HT crops in 2004 and 61% of U.S. soybean acres were in low- or no-till cropping systems—more than double the percentage claimed by Pimentel.
Pimentel states that “herbicides are the most serious pesticide pollutants in streams and groundwater in the United States.” More accurately, herbicides are the most common pesticide pollutant. This is mostly in the form of seasonal triazine herbicide contamination of surface waters. Characterizing this contamination as “serious” is debatable, given the relatively benign risk profile of triazine herbicides. Nor does this have much relevance to the spectrum of herbicides commonly used in biotech HT crops, such as glyphosate.
Glyphosate is rarely a significant contaminant of ground or surface waters owing to its rapid breakdown in the environment. As noted by Fernandez-Cornejo and McBride (1), the “substitution caused by the use of herbicide-tolerant soybeans results in glyphosate replacing other synthetic herbicides that are at least three times as toxic and that persist in the environment nearly twice as long.”
They further note that “Glyphosate binds to the soil rapidly, preventing leaching, and is biodegraded by soil bacteria. In fact, glyphosate has a half-life in the environment of 47 days, compared with 60-90 days for the herbicides it commonly replaces. In addition, glyphosate has extremely low toxicity to mammals, birds, and fish. The herbicides that glyphosate replaces are 3.4 to 16.8 times more toxic, according to a chronic risk indicator based on EPA reference dose for humans.” (1)
The World Health Organization, in its comprehensive study of pesticides and chemical contaminants in water (2), places glyphosate in a category where “it is unnecessary to recommend a health-based guideline value for these compounds because they are not hazardous to human health at concentrations normally found in drinking water.”
Pimentel cites a completely outdated statistic from 1994—prior to the introduction of biotech HT crops—when he claims that “95% of corn production acreage in Iowa receives herbicides, and 70% of this land is also cultivated for weed control.” This statistic is no longer relevant, given the significantly increased spectrum of herbicides and HT corn combinations available to Iowa farmers today, nearly ten years after the introduction of HT biotech crops. As Iowa State University weed scientist Dr. Mike Owen states, “tillage practices in Iowa corn production have changed considerably since 1994.” (Owen, personal communication, 2005)
Pimentel claims that “soil erosion is a serious problem in the United States” and states that “agricultural soil is being lost at about 10 times faster than soil reformation and sustainability.” While Pimentel may or may not have accurately cited what is claimed in the 2003 National Academy of Sciences publication, a nearly identical claim by Dr. Pimentel was extensively debated in the pages of Science in 1999 between Dr. Pimentel and soil geomorphologist and erosion specialist Dr. Stanley Trimble of the University of California, Los Angeles. (Science, vol. 286:1477) http://www.sciencemag.org/cgi/content/full/286/5444/1477c
In their 1999 exchange in Science, Pimentel and Skidmore cited a USDA report (3) in which U.S. soil erosion rates were estimated at 13 Mg per hectare per year (13 tons per hectare per year), as well as another paper (4) where erosion rates were estimated at slightly less than 12 Mg per hectare per year. Pimentel and Skidmore then cited Troeh et al. (5) when claiming that “this erosion rate is a factor of 12 higher than soil sustainability, on the basis of the average rate of soil formation.”
Dr. Trimble responded to these claims first by noting that, in fact, the 13 tons per hectare per year figure is not an actual measurement of soil loss, but is an estimate “from models, and they do not predict movement of sediment to streams. If U.S. soils have indeed been eroding at such rates over the last two or so decades, where are the detritus and efflux?”
Trimble further noted that “Troeh et al., on the basis of USDA information, state that the soil-loss tolerances for U.S. soils range from 2.2 to 11.0 Mg ha-1 year-1 (2, p. 115). U.S. agriculture is mostly on soils with a soil-loss tolerance of 11 Mg ha-1 year-1 or more (3, p. 678). Hence, there appears to be little disparity between soil-loss tolerance and what Pimentel and Skidmore say is the rate of erosion. Even according to the USDA study cited by Pimentel and Skidmore, only one-third of U.S. agricultural land is eroding faster than the sustainable rate—a statement that remains to be proven. Although erosion rates may be periodically high in some regions, U.S. soil erosion remains a problem but does not seem to be a crisis.”
In other words, Pimentel’s past claims that agricultural soil is being lost 10+ times faster than soil reformation and sustainability is not supported by the papers he himself cites. It is important to note that this exchange came in response to an extensive, 20+ year physical analysis of actual soil loss for one entire highly-erodible basin in Wisconsin (Coon Creek) conducted by Dr. Trimble and published in Science. (Science, vol. 285:1244-1246, 1999) This exhaustive study found rates of soil loss to be far lower than those estimated by the USDA models cited by Dr. Pimentel and Skidmore. As such, U.S. soil losses are likely well below tolerable soil loss rates and are sustainable.
Moreover, there is simply no denying that genetic engineering has and will make possible even further reductions in soil loss from cropland, far below those possible through the tillage-dependent organic farming propagandized by Dr. Pimentel.
Finally, Dr. Pimentel mistakes our statement that “Humanity already farms more than one-third of the Earth’s total land area” as referring only to cropland, which Pimentel correctly notes is 11% of the earth’s total land area. Farmed land is both cropland and land in pasture and rangeland (26%), making the total estimated farmed area 37% of the total global land area. Accounting for pasture and rangeland is clearly relevant when the primary organic fertilizer is animal manure.
Alex Avery
Tom DeGregori
References:
1. Fernandez-Cornejo, Jorge and William D. McBride. 2004. ‘Adoption and Pesticide Use’, pp. 26-29 in Adoption of Bioengineered Crops By Jorge Fernandez-Cornejo and William D. McBride. ERS/USDA (Economic Research Service, United States Department of Agriculture) Agricultural Economic Report No. AER810. 67 pp, May 2002. http://ers.usda.gov/publications/aer810/aer810h.pdf.
2. WHO (World Health Organization). 1998. Guidelines for Drinking-Water Quality, 2nd edition, Volume 1 – Recommendations – Addendum – Health Criteria and Other Supporting Information, Annex 2. Tables of Guideline Values – Table A 2.2 – Chemicals Not of Health Significance at Concentrations Normally Found in Drinking Water. Geneva: World Health Organization.
3. Summary Report: 1992 National Resource Inventory (USDA, Soil Conservation Service, Washington, DC, 1994).
4. N. D. Uri and J. A. Lewis, J. Sustainable Agric. 14, 63 (1999)
5. F. R. Troeh, J. A. Hobbs, R. L. Donahue, Soil and Water Conservation (Prentice Hall, Upper Saddle, NJ, 1999)
