“Soybean production is killing us,” notes Larry Gates of the Minnesota Department of Natural Resources. Southeast Minnesota, which once boasted clean rivers and streams, is increasingly inhospitable to healthy and diverse aquatic life—as well as to the people who flocked to those waters to fish and swim. Encouraged by Farm Bill incentives, Minnesota farmers have been converting their pastures and grasslands to soybean fields. That simple switch has had a profound impact, as endless rows of soybean plants have led to unprecedented levels of erosion. Load upon load of sediment has been washed into the river. As a result, brown trout populations, which had been rising for decades, are declining to the point where hundreds of thousands of young trout will have to be placed in the river if the population is to be maintained.1
Producing food animals, and the grains and soybeans that speed their growth, takes a tremendous toll on farmland—particularly its precious topsoil. Growing crops for animal feed frequently erodes the
soil, as does overgrazing of grasses by livestock. Further, cattle’s constant trampling of vulnerable rangeland can almost irreparably damage the environment. The immense quantities of fertilizers—including old-fashioned manure, urban processed sewage sludge, and conventional chemicals—and pesticides used to grow feed grains contain nutrients and toxins that disrupt the soil ecosystem, poison wildlife, and pollute local and far-off waterways.
Agriculture has an enormous impact on soil and soil quality: Grazing land and cropland are the second- and third-largest uses of land in the United States (forests are the largest), together accounting for just under half of America’s total acreage.2 In contrast, urbanization and sprawl affect only about 3 to 5 percent of the U.S. land area.3
Importance of Good Topsoil
Soil, along with water and sunlight, is one of the three fundamental elements of crop production. A thick layer of topsoil, rich in such nutrients as nitrogen, phosphorus, and potassium, absorbs and holds rainwater well and provides the best environment for growing crops.
But topsoil can be lost, leached away by water or blown away by wind. The U.S. Department of Agriculture (USDA) estimates that almost 2 billion tons of topsoil eroded from cropland in 2001.4 That’s a huge amount, but represents a 40 percent decline since 1982. The main cause of erosion is the lack of plants that hold the soil in place. Native meadow grasses, hay, and small grains such as wheat help protect topsoil by providing a solid cover over a field.5 Many large farms, however, plant livestock feed crops, such as corn and soybeans, that are grown in rows and endanger topsoil since the bare patches between each row are relatively susceptible to erosion. The loss of topsoil reduces fertility,6 which increases the need for chemical fertilizers. And the switch from healthy natural topsoil to artificial nutrients leads to a whole host of problems—nutrient imbalances, runoff, and water pollution—detailed later in this chapter.
Livestock’s Demand on Soil
Feeding grain to livestock and then eating the livestock (or their eggs or milk) needs a lot more land than just eating the grains themselves. Raising livestock creates a huge demand for corn, soybeans, and a few other crops. About 66 percent of U.S. grain ends up as livestock feed at home or abroad.7While pigs and chickens consume a good share of that grain, cattle at feedlots are the biggest consumers, in part because they are the least efficient converters of grain to meat. Outside the United States, livestock consume only 21 percent of total grain production, with the vast majority of grain consumed directly by people. But as nations’ incomes rise, so does their appetite for pork, chicken, and grain-fed beef.
Frequently, farmers respond to the huge demand for feed grains by turning to monocropping—raising single crops over huge areas—or they use limited rotations, where two crops destined for livestock feed are raised in alternating years. About 16 percent of corn—over 12 million acres—is raised without any rotation at all, though the majority of corn—59 percent—is rotated with soybeans.8 Meadow grasses and small grains (such as wheat), both vital to the preservation of topsoil, are included in only 8 percent of corn rotations, according to the USDA.9
Good soil health depends on several factors, including maintaining nutrient and organic matter content and avoiding topsoil loss.10 Robust crop variation—including seasons when land remains fallow altogether—is critical to maintaining optimal soil health. Including soybeans in a rotation helps maintain nutrient levels because soybeans and other legumes can “fix” nitrogen (the process by which bacteria convert nitrogen from its
relatively inert gaseous form in the atmosphere into compounds useful as nutrients, such as nitrate). However, soybeans, because they leave little residue on the field after harvest, are even less protective of topsoil loss than corn.11
A typical acre of U.S. cropland loses 5 tons of soil each year.12 About 20 percent of cropland—some 65 million acres—erodes at a rate that actually decreases its productivity.13 The resulting nutrient losses and lowered yields cost almost $10 billion per year (see table 1). And soil’s reduced water-holding capacity is not only costly (an estimated $3.2 billion per year) but self-perpetuating. It increases the rate of further erosion because unabsorbed water flows over the soil, with less water remaining for plants. Eroded soils therefore likely need more irrigation than “healthy” land—but irrigation, in turn, promotes more erosion.
The problems caused by cropland erosion extend well beyond the farm. Soil carried away by wind creates dust and haze and causes respiratory illnesses and property damage, which together cost over $14 billion per year.14Impaired water quality, due to sediment damage from agricultural runoff, accounts for about one-third of the cost of erosion. When soil is deposited into water, the suspended particles block sunlight, impairing the growth of
aquatic plants and depriving animals that feed on them of food. Sediment can also raise water temperatures, disrupting the habitats of aquatic species. But perhaps the greatest harm is not from the soil itself, but from fertilizers and pesticides that attach to soil particles.18 The cost of water pollution from erosion is estimated at $14 billion per year—and that doesn’t take into account the health and environmental harm from runoff from agricultural chemicals.19
Compaction occurs when topsoil—particularly when it is wet—is subjected to the intense weight of the heavy machinery farmers use to cultivate, plant, and harvest fields and of large livestock such as cattle—though machinery typically is the more damaging.21 Compaction makes soil too dense for plant roots to penetrate easily, reducing the rates of plant growth and crop yields.22 It also reduces soil’s ability to absorb water. The American Society of Agricultural Engineers found that pasture grazed by cattle for 10 years absorbs less than one-fifth as much water as ungrazed pasture.23 One consequence of compaction is erosion, because water that is not absorbed runs off, carrying topsoil with it.
Soil compaction is a major problem on western rangelands where cattle congregate in the biologically rich areas along the banks of waterways or in wetlands. That compaction reduces the capacity of those wetlands and soil to hold water, which leads to greater flooding and inhibits the recharging of water tables.
Compaction poses a different, but not a lesser, problem in the arid and semiarid regions of the West. Few grasses, bushes, and other plants grow on these lands. Instead, the main soil covering is an interconnected community—collectively referred to as microbiotic crust—of mosses, lichens, and cyanobacteria. (This last is an unusual form of bacterium that uses chlorophyll and other pigments to capture light for photosynthesis.) Crusts help hold soil nutrients, control water absorption, and create a medium for plant growth. Although tough enough to support life in some of the hottest, driest climates in the United States, crusts are quite vulnerable to physical disturbances. Because the crusts are only 1 to 4 millimeters thick (less than one-sixth of an inch), compaction and grazing by cattle can easily destroy them. And that destruction inevitably leads to erosion, water loss, and harm to native plant species. Moreover, crust recovers extremely slowly. Full regeneration takes 50 to 250 years, depending on the extent of damage, according to government scientists.24
New Practices Help, but More Help Is Needed
Over the past two decades, farmers have used various measures to better conserve farmland. And that has paid off: In 1982, 3 billion tons of topsoil eroded from cropland. By 1997, that figure was reduced by 40 percent to just under 2 billion tons.26 But in some areas, soil losses remain well above levels of sustainability.
Several factors account for the dramatic improvement in soil conservation. For starters, the USDA’s Conservation Reserve Program (CRP) has paid tens of thousands of farmers to idle their most erodible lands, thereby dramatically improving soil health.[*] The CRP idles about 35 million acres of land.27 Only about 1 percent of CRP land, fewer than 1 million acres, is eroding at an unsustainable rate.28,[+] That success is impressive, particularly since most of the land included in the program was experiencing serious erosion. The CRP shows that even in extreme cases, strong (though expensive) measures can protect the land.
Farmers also have reduced erosion by using conservation tillage or reduced tillage on roughly half the nation’s cropland. That practice cuts back on plowing and leaves crop residue (such as cornstalks) on the ground after harvest to prevent erosion.29 “No-till” agriculture, which is facilitated by genetically engineered herbicide-tolerant soybean and corn varieties, barely disturbs soil from planting to harvest time.30 Farmers also have been planting buffer strips or terracing land to help reduce erosion.
Topsoil losses persist nonetheless. Reducing or eliminating the need for corn, soybeans, wheat, and other grains for livestock feed—especially for cattle—could further reduce erosion. In theory, ceasing
[*]CRP land may be grazed or cut for hay under emergency conditions such as drought or an animal feed shortage, but it otherwise remains fallow.
[+]Though the vast majority of acres enrolled in the CRP are “highly erodible land,” other lands are also enrolled to protect wildlife habitats and water quality and to address other environmental problems. Inclusion of those acres lowers the average rate of erosion on CRP land.
Wind erosion still occurs on about 420,000 acres of CRP land and water erosion on 365,000 acres, with some land experiencing both types of erosion. However, even if there were no overlap, only 2.4 percent of all CRP land would experience erosion-induced productivity losses.
grain production for livestock would allow close to 100 million acres to lie fallow and revert to natural grasslands and woodlands.31 That shift could save as much as 700 million tons of topsoil per year. In reality, though, much of that land would be used to grow crops for export or for conversion to gasohol, high-fructose corn syrup, and other products, and some would be planted in crops that would replace some of the meat in our diet.
Effects of What We’re Putting on the Soil
Loss of topsoil decreases productivity, so to compensate for that farmers add soil nutrients. That means applying fertilizer—and lots of it—in the form of chemicals, manure, or treated sewage sludge.
Fertilizer causes environmental problems primarily because farmers often apply too much to their land. Because about half of all fertilizer applied in the United States is used solely for raising feed grains for animals, reducing that usage could reduce environmental degradation.32
Even when not over-applied, nitrogen fertilizer causes serious environmental problems. That fertilizer is usually applied as ammonium nitrate, which can react with oxygen in the air and release ammonia. Ammonia can damage local ecosystems, including the plant life on the fertilized land.33 When carried by wind and rain, the ammonia may be deposited in waterways and affect distant ecosystems (see “Ammonia,” p. 104, for further details).
When the oxygen content of soil is low, nitrogen fertilizer undergoes a process called denitrification, which yields a variety of nitrogen-containing gases, including nitrogen gas, nitric oxide and nitrogen dioxide (which are together known as NOx, since, in the presence of sunlight, they rapidly interconvert), and nitrous oxide.[*] The harmless nitrogen gas simply returns
[*]The fact that oxygen-containing species are produced may seem strange considering that the reaction takes place in the absence of oxygen. What actually happens is that in oxygen-poor conditions, anaerobic bacteria strip the oxygen from nitrogen dioxide (which occurs naturally in soil or is deposited by acid rain), releasing nitrogen gas and nitric oxide into the atmosphere. Oxygen in the atmosphere readily recombines with those gases to produce nitrous oxide and NOx.
to the atmosphere. However, NOx destroys ozone, impairs lung function, and contributes to fog and acid rain.35 It also travels even farther from its source than ammonia.36 Nitrous oxide is a destructive greenhouse gas 300 times more potent than carbon dioxide (for more on this topic, see “Nitrous Oxide” and “Nitric Oxide and Nitrogen Dioxide,” pp. 107 and 108).37Agriculture contributes about 37 percent of all nitrous oxide releases in the United States, with much of that coming from fertilizer.
Besides polluting the air, fertilizers also increase the acidity of soil.38 That reduces the soil’s ability to hold nutrients and can permanently reduce soil productivity. Acidification ordinarily is controlled by applying even more chemicals, such as lime (calcium carbonate).
Heavy Metals in Chemical Fertilizer
The potash and phosphate ores used to produce chemical fertilizers frequently contain heavy metals that may contaminate the soils on which they are used. Those contaminants can be absorbed into the grains grown in the soil, the livestock that consume those grains, and eventually the people who consume the resulting meat and dairy products.39 The U.S. Environmental Protection Agency recognizes that cadmium, lead, arsenic, zinc, and other minerals sometimes contaminate fertilizer.40 With intensive application of nitrogen, phosphate, and potassium fertilizers, cadmium and lead levels in soil can double in a dozen years.41 Liming materials, such as sludge from water treatment facilities (see “‘Biosolids’ Fertilizer: Processed Sludge,” p. 84), also contain a potpourri of heavy metals, including mercury.42 So when liming materials are used to reduce the acidity of soil, they also may pollute it.
A 1999 study of toxic waste in California by the nonprofit Environmental Working Group found that one in six samples of commercial fertilizers exceeded the state’s criteria for what constitutes hazardous waste. Among the heavy metals detected, lead and arsenic were present in the greatest amounts.43
The concentrations of metals may be even greater in manure than in chemical fertilizers, and transferring them to soil may lead to higher levels in food crops.44 In fact, many poultry farmers add to feed an arsenic-
containing drug, roxarsone, to kill parasites that slow the animals’ growth. The U.S. Geological Survey states that each year the poultry litter that is spread onto nearby fields contains 2 million pounds of roxarsone and “could result in localized arsenic pollution.”45 Johns Hopkins University
researchers warn that “If animal waste were classified as hazardous waste, it would be prohibited from land disposal based solely on its concentrations of leachable arsenic.”53
“Biosolids” Fertilizer: Processed Sludge
To address their waste-disposal problems, cities sell treated sewage sludge—biosolids—to farmers cheaply as fertilizer. Sixty percent of processed urban sewage sludge—3.4 million tons per year—is now applied as fertilizer. In theory, that approach is mutually beneficial, because it enables cities to dispose of their waste, while providing farmers with affordable fertilizer. The one problem—and it’s a significant one—is that sewage can be tainted with industrial waste and pathogens.54 Government regulations are supposed to restrict levels of heavy metals; volatile organic chemicals; and pathogenic bacteria, viruses, and parasites.55 But the controls sometimes fail. In 2003, hundreds of cows at Georgia dairy farms died after they ate hay grown on fields fertilized by processed sewage sludge.56
Currently, fertilizer manufacturers are not required to disclose heavy-metal content on product labels, so the full extent of the problem is unknown. To date, only Washington and Texas limit heavy-metal contaminants (including those from industrial sludge) in fertilizer.57
Pesticides: Gauging the Health Risk
Large amounts of pesticides—and potentially dangerous (and misnamed) inert chemicals included in pesticide products—continue to be applied to soil, though the current volume is 40 percent less than was used in the late 1970s and early 1980s.58 Pesticides can unintentionally harm plants and animals; organisms living in the soil; and fish and other animals, plants, and microorganisms in the waterways into which the chemicals are carried. Because they adhere to particles in soil, pesticides can be carried long distances on dust and then tracked into homes and public spaces.
Glyphosate (marketed under the name Roundup) and atrazine are the two most widely used herbicides, helping control weeds on millions of acres of soybeans, corn, and other crops. Over 100 million pounds of those two pesticides are used every year. Even though their half-lives are moderate (between 30 and 100 days, depending on environmental conditions59), significant residues still may be present in soil after a year.
Because of their widespread use, scientists have explored the possible environmental and health effects of glyphosate and atrazine. Both have been implicated in the decreases in amphibian populations seen in the upper Midwest and elsewhere around the world. University of Pittsburgh
researchers have discovered that a supposedly inert ingredient in glyphosate endangers amphibians.60 Rick Relyea and two colleagues studied the detergent (polyethoxylated tallowamine) that helps glyphosate get into plant leaves. At doses that are likely to occur in nature, the detergent kills tadpoles and frogs. Relyea considers Roundup “extremely lethal to amphibians.”
Atrazine, used by most corn farmers, also affects amphibians. Tyrone Hayes and his colleagues at the University of California at Berkeley exposed frogs to levels of atrazine lower than what is permitted in drinking water and found that the herbicide caused gonadal and limb abnormalities and hermaphroditism.61 Hayes uses the term “chemical castration,” and says, “because the hormones that are being interfered with occur in all vertebrates, maybe they’re telling us it’s just a matter of time” before atrazine is found to harm humans.62
Pesticides eventually are broken down in the soil by microorganisms or through chemical reactions, or they are carried into groundwater or streams. Some of the harm they can cause there is discussed in “Pesticides Wash Off of Farmland,” p. 100.
What It All Means
Healthy topsoil is crucial to producing crops, but modern agriculture has placed extraordinary demands on cropland. The enormous quantities of feed grains that farmers produce help satisfy our desire for inexpensive meat and dairy products—but at great cost to topsoil, the environment, and even human health. The row crops that stretch from one end of the horizon to the other in many parts of the United States provide less anchorage for topsoil, increasing erosion. The chemical and biosolids fertilizers applied to farmland sometimes upset the balance of nutrients, as well as release into the atmosphere gases that harm human health and the environment. And the pesticides applied to the land and crops disrupt ecosystems, harm wildlife, and—as discussed in “Risks from Pesticides,” p. 53—endanger farmworkers and possibly consumers.
(Please note: this page numbered 201 to match placement of endnotes in printed edition)
1. C. Niskanen, “Trout in troubled waters: shifts in land use in southeast Minnesota are causing sediment damage to streams,” St. Paul Pioneer PressApr. 17, 2005:7G.
2. U.S. Department of Agriculture, Economic Research Service (USDA ERS), “Briefing room: land use, value, and management: major uses of land” (2002), www.ers.usda.gov/Briefing/LandUse/majorlandusechapter.htm, accessed May 2, 2003.
3. G. Wuerthner, freelance biologist and former employee of U.S. Bureau of Land Management, email to Center for Science in the Public Interest (CSPI), Sept. 16, 2004.
4. U.S. Department of Agriculture, Natural Resources Conservation Service (USDA NRCS), National Resources Inventory 2001 NRI: Soil Erosion (2003), www.nrcs.usda.gov/technical/land/nri01/erosion.pdf.
5. USDA ERS, Agricultural Resources and Environmental Indicators(Washington, DC, 2003), p. 4.2-15.
6. M. Al-Kaisi, “Soil erosion and crop productivity: topsoil thickness” (Ames, IA: Iowa State University, 2001), www.ipm.iastate.edu/ipm/icm/2001/1-29-2001/topsoilerosion.html.
7. The 37 percent figure is from United Nations Development Programme, United Nations Environment Programme, World Bank, and World Resources Institute, World Resources 2000–2001: People and Ecosystems—The Fraying Web of Life (Washington, DC, 2001), pp. 258–59.
8. USDA ERS, Agricultural Resources, pp. 4.2-14, 15.
9. USDA ERS, Agricultural Resources, pp. 4.2-14, 15.
10. USDA ERS, Soil, Nutrient and Water Management Systems Used in U.S. Corn Production (Washington, DC, 2002), p. 9.
11. USDA ERS, Agricultural Resources, pp. 4.2-14, 15.
12. USDA ERS, Summary Report 1997 National Resources Inventory(Washington, DC, 2000), pp. 51, 57. Much of the data on soil erosion in this chapter are adapted from that report. Although the 2002 Inventory has been published, it is not as exhaustive as the 1997 report, and USDA maintains that data from the 1997 report are more reliable and consistent. For further explanation, see www.nrcs.usda.gov/technical/NRI/.
13. USDA ERS, Summary Report, pp. 58–95. USDA NRCS estimates that water erosion impairs crop productivity on about 65 million acres, and wind erosion impairs productivity on 48 million acres. Some of that land experiences both types of erosion. Current national data do not allow distinguishing the extent of erosion related to different crops. If those data were available, one could estimate the erosion resulting from animal agriculture.
14. USDA NRCS, Managing Soil Organic Matter: The Key to Air and Water Quality (2003),
15. P. Sullivan, Overview of Cover Crops and Green Manures: Fundamentals of Sustainable Agriculture (National Sustainable Agriculture Information Service, 2003), http://attra.ncat.org/attra-pub/PDF/covercrop.pdf.
16. USDA ERS, Summary Report, pp. 58–59.
17. USDA NRCS, “What is topsoil worth?,”http://soils.usda.gov/sqi/concepts/soil_organic_matter/som_d.html, accessed Dec. 26, 2005.
18. W.R. Osterkamp, hydrologist, U.S. Geological Survey, email to CSPI, Apr. 25, 2003.
19. USDA NRCS, Managing Soil Organic Matter.
20. A. Fletcher, “Soil erosion could devastate food sector” (2006),www.foodnavigator.com/news/ng.asp?n=66605-soil-nutrients-crops.
21. USDA Agricultural Research Service (USDA ARS), “Technologies for management of arid rangelands,” research project description (2001),www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=142788; J. Daniel, Grazinglands Research Laboratory, USDA ARS, email to CSPI, Apr. 28, 2003; and J.A. Daniel and W.A. Phillips, “Impacts of grazing strategies on soil compaction,” paper presented at American Society of Agricultural Engineers 2000 Summer Meeting, Milwaukee, July 9–12, 2000.
22. A.J. Jones, R.D. Grisso, and C.A. Shapiro, “Soil compaction … fact and fiction: common questions and their answers” (Lincoln: University of Nebraska Cooperative Extension Service, 1988), http://ianrpubs.unl.edu/soil/cc342.htm.
23. J.A. Daniel, P. Kenneth, W. Altom, et al., “Long-term grazing density impacts on soil compaction,” Trans ASAE (2002) 45:1911–15.
24. U.S. Geological Survey, “An introduction to biological soil crusts,”www.soilcrust.org/crust101.htm, accessed June 17, 2004.
25. J. Belsky and J.L. Gelbard, “Comrades in harm: livestock and weeds in the intermountain west,” in G. Wuerthner and M Matteson, eds., Welfare Ranching: The Subsidized Destruction of the American West (Washington, DC: Island Press, 2002), pp. 203–06.
26. USDA NRCS, Summary Report 1997 National Resources Inventory(Washington, DC, 2000), p. 9. For similar 2003 data, see USDA, “Johanns announces 43 percent decline in total cropland erosion,” press release, May 22, 2006, www.usda.gov/2006/05/0170.xml.
27. USDA Farm Service Agency, Conservation Reserve Program monthly contract report, www.fsa.usda.gov/crpstorpt/06Approved/r1sumyr/us.htm, accessed Aug. 3, 2005.
28. USDA NRCS, National Resources Inventory: 2002 (Washington, DC, 2004), p. 1.
29. USDA, Agricultural Resources and Environmental Indicators(Washington, DC, 2003), ch. 4.2, pp. 22, 41.
30. Purdue University, “Tillage type definitions” (2002), www.ctic.purdue.edu/Core4/CT/Definitions.html.
31. Calculations based on acreages in USDA, National Agricultural Statistics Service (USDA NASS), Agricultural Chemical Usage: Field Crops Summary for 1998, 2000, 2001; and grain used for feed from Agricultural OutlookSept. 2002, www.ers.usda.gov/publications/agoutlook/sep2002/ao294.pdf, p. 44, table 17.
32. Calculations based on acreages in USDA NASS, Field Crops Summary for 1998, 2000, 2001. Total U.S. fertilizer use in 2001 was 20.6 million tons according to USDA ERS, “Agricultural chemicals and production technology: questions and answers, 2002,” ERS Online Briefing Room,www.ers.usda.gov/Briefing/AgChemicals/Questions/nmqa2.htm, accessed Mar. 23, 2004.
33. C.E. Pitcairn, U.M. Skiba, M.A. Sutton, et al., “Defining the spatial impacts of poultry farm ammonia emissions on species composition of adjacent woodland groundflora using Ellenberg Nitrogen Index, nitrous oxide and nitric oxide emissions and foliar nitrogen as marker variables,”Environ Pollut (2002) 119:9–21.
34. Adapted from USDA NASS, Milk Production, Disposition, and Income 2002 Summary (Washington, DC, 2003), p. 2; USDA NASS, Poultry Slaughter 2002 Summary (Washington, DC, 2003), p. 2; USDA NASS, Livestock Slaughter 2002 Summary (Washington, DC, 2003), pp. 35, 41, 49; and USDA NASS, Chickens and Eggs 2003 Summary (Washington, DC, 2004), p. 2.
35. National Research Council (NRC), Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs (Washington, DC: National Academies Press, 2003), ch. 3.
36. United Nations Industrial Development Organization, Technical Report No. 26 Part 1: Mineral Fertilizer Production and the Environment (Geneva, 1998), p. 49; and NRC, Air Emissions, p. 75.
37. Potash and Phosphate Institute and Potash and Phosphate Institute of Canada (PPI-PPIC), Technical Bulletin 2002–1: Plant Nutrient Use in North American Agriculture—Producing Food and Fiber, Preserving the Environment, Integrating Organic and Inorganic Sources (Norcross, GA, 2002), p. 60.
38. D. Eckert, “Efficient fertilizer use: fertilizer management practices” (Bannockburn, IL: IMC-Agrico),www.agcentral.com/imcdemo/05Nitrogen/05-0.htm; and A. Napgezek,
“Aging soils?,” University of Wisconsin Extension NPM Field Notes Feb./Mar. 1999.
39. H. de Zeeuw and K. Lock, “Urban and periurban agriculture, health and environment,” discussion paper for Food and Agriculture Organization of the United Nations-Resource Centre for Urban Agriculture and Forestry electronic conference, Urban and Periurban Agriculture on the Policy Agenda (2000), www.fao.org/urbanag/Paper2-e.htm.
40. U.S. Environmental Protection Agency, Office of Pollution Prevention and Toxics (EPA OPPT), Background Report on Fertilizer Use, Contaminants, and Regulations (1999), www.epa.gov/opptintr/fertilizer.pdf, pp. ii, iv; and U. Krogmann and L.S. Boyles, Land Application of Sewage Sludge (Biosolids), No. 5: Heavy Metals (New Brunswick, NJ: Rutgers University Agricultural Experiment Station, 1999).
41. EPA OPPT, Background Report, p. 112.
42. EPA OPPT, Background Report, p. 110.
43. J. Kaplan, Z. Ross, and B. Walker, As You Sow: Toxic Waste in California Home and Farm Fertilizers (San Francisco: California Public Interest Research Group, 1999), p. 1.
44. PPI-PPIC, Technical Bulletin, p. 48.
45. R.L. Wershaw, J.R. Garbarino, and M.R. Burkhardt, “Roxarsone in natural water systems,”
in U.S. Geological Survey, Proceedings: Effects of Confined Animal Feeding Operations (CAFOs) on
Hydrologic Resources and the Environment, meeting held in Fort Collins, CO, Aug. 30–Sept. 1, 1999,http://water.usgs.gov/owq/AFO/proceedings/afo/html/wershaw.html.
46. Based on manure data in R.L. Kellogg, C.H. Lander, D.H. Moffitt, et al.,Manure Nutrients Relative to the Capacity of Cropland and Pastureland to Assimilate Nutrients: Spatial and Temporal Trends for the United States(Washington, DC: USDA, 2000), p. 49; and USDA NASS data on numbers of livestock, www.nass.usda.gov:8080/QuickStats/indexbysubject.jsp?Pass_group=Livestock+%26+Animals.
47. Based on a midyear population of 285,317,559 from the U.S. Census Bureau, “State population estimates: April 1, 2000 to July 1, 2002,”www.census.gov/popest/archives/2000s/vintage_2002/ST-EST2002-01.html, accessed Jan. 13, 2003; and an average waste generation of about 0.518 tons per person per year from EPA, National Pollutant Discharge Elimination System Permit Regulation and Effluent Limitation Guidelines and Standards for Concentrated Animal Feeding Operations (CAFOs), as cited in Fed Reg (2003) 68(29):7175–274 (complete document is atwww.epa.gov/EPA-WATER/2003/February/Day-12/w3074.htm).
48. Adapted from American Society of Agricultural Engineers, Manure Production and Characteristics (St. Josephs, MI, 2002), pp. 687–89; and Kellogg et al., Manure Nutrients, p. 49.
49. Kellogg et al., Manure Nutrients, p. 74.
50. Council for Agricultural Science and Technology, Storing Carbon in Agricultural Soils to Help Mitigate Global Warming, CAST Issue Paper 14(Washington, DC, 2000), p. 2; and Kellogg et al., Manure Nutrients, pp. 53, 56.
51. PPI-PPIC, Organic or Inorganic, Which Nutrient Source Is Better for Plants?, Enviro-briefs No. 2 (Norcross, GA, 2002).
52. University of Maryland Cooperative Extension Service, Nutrient Manager: Making the Most of Manure (College Park, MD, 1994).
53. K.E. Nachman, J.P. Graham, L.B. Price, and E.K. Silbergeld, “Arsenic: a roadblock to potential animal waste management solutions,” Environ Health Perspect (2005) 113(9):1123–24.
54. J.E. Lee, “Sludge spread on fields is fodder for lawsuits,” New York TimesJune 26, 2003:20.
55. EPA, Office of Enforcement and Compliance Assurance, Land Application of Sewage Sludge: A Guide for Land Appliers on the Requirements of the Federal Standards for the Use or Disposal of Sewage Sludge, 40 CFR Part 503 (1994), www.epa.gov/owm/mtb/biosolids/sludge.pdf.
56. Lee, “Sludge.”
57. EPA OPPT, Background Report, p. iii.
58. R. Kellogg, R. Nehring, A. Grube, et al., “Trends in the potential for environmental risk from pesticide loss from farm fields” (USDA Natural Resources Conservation Service, 1999), www.nrcs.usda.gov/technical/land/pubs/pesttrend.html.
59. Extension Toxicology Network, Movement of Pesticides in the Environment, Toxicology Information Brief (1993), http://extoxnet.orst.edu/tibs/movement.htm.
60. “Roundup kills frogs as well as tadpoles, Pitt biologist finds,” University of Pittsburgh news release, Aug. 3, 2005, www.umc.pitt.edu:591/m/FMPro?-db=ma&-lay=a&-format=d.html&id=2115&-Find; and “Roundup highly lethal to amphibians, finds University of Pittsburgh researcher,” Medical News Today Apr. 3, 2005, www.medicalnewstoday.com/medicalnews.php?newsid=22159.
61. T. Hayes, K. Haston, M. Tsui, et al., “Atrazine-induced hermaphroditism at 0.1ppb in American leopard frogs (Rana pipiens): laboratory and field evidence,” Environ Health Perspect (2003) 111(4):568–75; and L. Tavera-Mendoza, S. Ruby, P. Brousseau, et al., “Response of the amphibian tadpole Xenopus laevis to atrazine during sexual differentiation of the ovary,”Environ Toxicol Chem (2002) 21:1264–67.
62. M. Losure, “Frog researcher invited to tell his story,” Minnesota Public Radio, Oct. 26, 2004, http://news.minnesota.publicradio.org/features/2004/10/25_losurem_frogresearch/.