Crop residue burning occurs in all fifty states, including Alaska. In the contiguous United States nearly 20% of land is dedicated to crops. Residues from corn, cotton, rice, soybean, sugar cane, wheat, grass seed (e.g. Kentucky bluegrass seed), horticultural crops, and fallow fields are most commonly burned. Crop residue burning in the United States takes two forms: (1) the practice of burning residues post-harvest whereby the residues consist of a layer of ground-level senescent vegetation, and; (2) the practice of burning residue pre-harvest (primarily used for sugarcane harvesting), whereby leaves and other biomass are burned prior to the harvest. In addition to burning crop residues both during and after harvest, fire is also used in cropland areas for pest and weed control and to prepare fields for planting. Crop residue burning helps growers stay competitive as it is an inexpensive and effective method to remove excess residue. This excess residue prevents future seeding by shading out the next crop and facilitating mold growth. Crop residue burning also provides a short-term ash fertilization effect.
Setting Fire to the Fields
The spectrum of technologies and systems used to set cropland fires and monitor crop residue burning in the United States ranges from very basic to complex. Depending on where a farmer lives, he or she may simply wake up and decide to burn without any requirements from local, state, or federal laws or agencies. However, he or she may have to plan their burn weeks in advance, pay for a permit to burn, and burn only on days that have been forecasted by state agencies as appropriate ‘burn’ days given local meteorological conditions. Some farmers retrofit old, metal gasoline cans for drip torches while others have equipped small farm machinery with actual torches. In both Arkansas and Idaho, local officials have reported seeing farmers set fire to old tractor tires and then drag these burning tires across the field in order to burn residues. In all cases, farmers aim to completely burn the crop residues within the field boundary.
Most states in the U.S. are so-called “freedom to farm” or “right to farm” states, whereby the state legislature can not pass a law which limits or prejudices agricultural activities or allows for nuisance lawsuits against agricultural activity. However, concerns over impaired air quality and visibility related to smoke from crop residue burning have forced many states to rethink past hands-off legislation on agricultural burning. For example, seven states, including Louisiana and Idaho, require that farmers must burn during the daytime only and that certified Burn Managers must be present at all fire events (Table 1). Because of the proximity of large urban areas such as West Palm Beach, Naples, and Miami, corporate and cooperative sugarcane farmers in Florida requested a burn policy and permit system to limit nuisance complaints. Since 2004, the Florida Department of Forestry issues daily burn permits, based on wind conditions, direction, and flammability. Agricultural burning policy in Washington is enforced by the Washington Department of Ecology under the 1991 Clean Air Act of Washington. The Washington Department of Ecology issues all burning permits and has the legal right to fine farmers $10,000 for any illegal crop residue burning.
Crop Residue Burning Regulations
Table 1. State- level regulations for crop residue burning in California, Florida, Louisiana, Oregon, and Washington.
Using remote sensing to quantify crop residue burning
Satellite monitoring of crop residue burning provides a systematic and reliable approach over large areas. For example, the Moderate Resolution Imaging Spectrometer (MODIS) flown on board the NASA Terra and Aqua satellites has been a key sensor for detecting and quantifying biomass burning, including crop residue burning. By combining both burned area data with actively burning data from the MODIS sensor, McCarty et al. (2009) estimated that 1,239,000 ha of croplands burn annually in the contiguous United States. The results of this analysis show that crop residue burning in the contiguous United States occurred consistently each year in specific regions, particularly the Mississippi Delta states of Arkansas, Mississippi, and Louisiana; the Blackbelt of southern Georgia and Alabama; the Everglades Agricultural Area in south Florida; the southern Great Plains of Texas, Oklahoma, and Kansas; the northern Great Plains of eastern Colorado, Minnesota, South Dakota, and North Dakota; the Snake River region in southern Idaho; the Inland Pacific Northwest of eastern Washington, northern Idaho, and northeastern Oregon; the Willamette Valley in Oregon; and the Central Valley of California. This spatial distribution is directly related to the kinds of crops grown within these regions, particularly wheat, soy, corn, rice, sugarcane, and grass seed. The thirteen states with the largest cropland burned area, in descending order, are: Florida, Arkansas, Idaho, California, Texas, Washington, Kansas, North Dakota, Colorado, South Dakota, Louisiana, Oklahoma, and Oregon.
Crop residue burning in Florida Florida is clustered in the Everglades Agricultural Area south of Lake Okeechobee (Figure 1). This agricultural area mainly grows sugarcane, which is harvested from October to April. Sugarcane fields are often burned prior to harvest to remove dead leaves and other so-called "trash" biomass that can impede mechanical and conventional harvesting, increase transportation costs, and absorb sugar during the milling extraction process. Nearly all sugarcane fields are burned prior to harvest. Sugarcane is a big agricultural industry in Florida, accounting for 25% of all domestic sugar production. On average, Florida farmers grow approximately 162,000 ha of sugarcane each year.
Historically, Kansas farmers used crop residue burning to remove excess biomass from the fields and to prevent plant diseases. Recent air pollution events in neighboring cities like Kansas City, Missouri from agricultural burning in Kansas have forced the state to investigate the necessity to monitor and restrict all forms of agricultural burning, including crop residue burning (Figure 2). Current state law allows farmers to burn agricultural residues as long as certain fire safety precautions are met under Kansas Air Regulation 28-19-648. Corn and soy residues are burned in eastern Kansas during the fall. Wheat residues account for the vast majority of cropland burning in Kansas. Wheat is harvested between late May and July, with a second burning season during September and October to clear fields before the fall planting.
Air quality and crop residue burning
Crop residue burning is a governmental, environmental, and health policy issue at the state and national level. As early as the 1970s, local and state governments in the U.S. had begun to debate the benefits of crop residue burning for farmers, citing the use of fire for pest and weed control as an easy, inexpensive removal method of residues to facilitate planting of the next crop, versus the detrimental impacts of these emissions on air quality. Due to the national growing awareness of the negative effect of crop residue burning on air quality, mainly through the enactment of the 1990 Clean Air Act by the U.S. federal government, more states in the contiguous United States have increased regulation of crop residue burning. In some states, compliance with the regulations is monitored through expanded in-situ, aerial photography, and satellite-based monitoring of agricultural fire and enforcement of prescribed crop residue burning permits, most commonly in the Pacific Northwest states of Washington, Idaho, and Oregon.
Concerns over impaired regional air quality forced the state of Idaho to go to court to defend the practice of crop residue burning. In the case Safe Air For Everyone v. U.S. Environmental Protection Agency, the U.S. Environmental Protection Agency (EPA) Region 10, a private grower, and the State of Idaho defended the practice of crop residue burning against three petitioners: Safe Air for Everyone (an environmental group), the American Lung Association of Idaho, and the neighbor of the aforementioned private grower. On January 30, 2007, the U.S. Ninth Circuit Court of Appeals ruled that a 2005 EPA decision to allow crop reside burning in Idaho was legally flawed. Due to the ruling, all field burning was banned until the state of Idaho could develop a new State Implementation Plan (SIP) that provides more regulation of the practice in accordance with the 1990 Clean Air Act and subsequent EPA regulation on air quality attainment. Citing tribal sovereignty, both the Nez Perce and the Coeur d'Alene tribes started burning Kentucky bluegrass fields within their tribal lands on August 13, 2007 and August 27, 2007, respectively. In 2008, the Idaho Legislature mandated the Idaho Department of Environmental Quality to manage all crop residue burning, which now requires all farmers to receive permits for burning, to pay a $2 fee per acre to burn, to complete burn management training within the past five years, and to follow all rules concerning no-burn days. As of September 2009, the Idaho Department of Environmental Quality had rewritten its SIP to regulate crop residue burning.
Future burning: the impact of climate change
The future of crop residue burning is an uncertain one. The United States loses croplands at a rate of roughly 2% every five years. With farmland becoming increasingly surrounded by real estate developments, farmers are likely to intensify agriculture in order to maintain current yields and profits. Intensification, in turn, could lead to increased burning as farmers add profitable crops, like rice, wheat, and corn, into their normal fallow rotation. Climate change will also alter the distribution of croplands and related burning by shifting growing zones northward and creating drier, less arable micro-climates in the southeast and southern Midwest (Cline, 2007). This northward trend could lead to crop residue fires shifting north, with more southern farmers using fire to stay competitive. Pest and noxious weed populations are projected to grow and expand northward as the climate warms (Coakley et al., 1999), which could increase fire activity in croplands as a mitigation tool. In addition, there is strong scientific consensus that climate change in the next century will lead to a shift to dryland farming due to precipitation increases across the contiguous United States. Dryland farming is defined as the absence of irrigation and a reliance on precipitation; it is sometimes referred to a 'rain-fed.' Dryland farming relies almost exclusively on no-till management practices, where by farmers do not plow. A byproduct of no-till agriculture is dramatically increased residue loads. These increased residues are often managed using fire.
Alternatives to crop residue burning
Current suggested alternatives include incorporating residues back into soils. It should be noted that this alternative requires tilling and could negatively impact many areas where top soil levels are low. In California, the Air Resources Board recommended using crop residues for offsite use, such as “energy production, as construction materials, in paper and cardboard, as compost for mushroom growing and soil amendment, [or] as cover for erosion control and landfill (1995)”. The Air Resources Board also noted that these offsite uses were not economically viable alternatives for most farmers except if there were future growth in energy production from crop residues, which has shown some promise in Brazil with biofuel production from sugar cane. In the state of Washington, Kentucky bluegrass seed farmers are now required to use herbicide, often referred to as “chemical burning”, as an alternative to burning residues. Seed growers in Washington have also sold their excess residues as livestock feed and bedding in nearby and neighboring states, though this is highly dependent on the presence of drought conditions which limit natural growth of pastures.
- Ball, D.A., Walenta, D.L., Rasmussen, P.E. 1998. Impact of nitrogen fertilization and stubble burning on the downy brome seedbank in a winter wheat fallow rotation. Journal of Production Agriculture 11(3): 342-344.
- Baucum, L.E., Rice, R.W., Schueneman, T.J. 2006. An Overview of Florida Sugarcane. In: Florida Sugarcane Handbook. pp. 1-6. University of Florida, Institute of Food and Agricultural Science, Florida Cooperative Extension Service, Gainesville, Florida. Online: http://edis.ifas.ufl.edu/pdffiles/SC/SC03200.pdf. Accessed: September 2008.
- Bottcher, A.B., Izuno, F.T. 1994. Everglades Agricultural Area (EAA): Water, Soil, Crop, and Environmental Management. pp. 32-36. University of Florida Press, Gainesville, Florida.
- Canode, C.L., Law, A.G. 1979. Thatch and tiller size as influenced by residue management in Kentucky bluegrass seed management. Agronomy Journal 71: 289-291.
- California Air Resources Board. 1995. Research Notes: The Economic Impacts of Alternatives to Crop Residue Burning. Online: http://www.arb.ca.gov/research/resnotes/notes/95-16.htm. Accessed September 2008.
- California Air Resources Board. 2006 California Air Resource Board: Smoke Management Program. Online: http://www.arb.ca.gov/smp/regs/regs.htm. Accessed: January 2008.
- Cline, W.R. 2007. Global Warming and Agriculture: Impact Estimated by Country. Washington, DC: Center for Global Development, Peterson Institute for International Economics.
- Coakley, S.M., Scherm, H., Chakraborty, S. 1999. Climate change and plant disease management. Annual Review of Phytopathology 37: 399-426.
- Dhammapala R, Claiborn C, Corkill J, Gullett B (2006) Particulate emissions from wheat and Kentucky bluegrass stubble burning in eastern Washington and northern Idaho. Atmospheric Environment 40: 1007-1015.
- FLDOF. 2005. Florida Division of Forestry Fire Management Information System. Online: http://www.fl-dof.com/fire_weather/index.html. Accessed: July 2007.
- Idaho Department of Environmental Quality. 2009. Air Quality: Crop Residue Burning. Online: http://www.deq.state.id.us/AIR/prog_issues/burning/crop_residue_burning.cfm. Accessed: September 2009.
- KDHE. 2008. Kansas Department of Health and Environment Open Burning Regulations. Online: http://www.kdheks.gov/befs/download/dist_offices/KS_Open_Burning_Regulations.pdf. Accessed: September 2008.
- Korontzi, S., McCarty, J., Loboda, T., Kumar, S., Justice, C.O. 2006. Global distribution of agricultural fires from three years of MODIS data. Global Biogeochemical Cycles, 20(6): 2021. doi: 10.1029/2005GB002529.
- Lapping, M.B., Penfold, G.E., Macpherson, S. 1983. Right-to-farm laws: Do they resolve land use conflicts? Journal of Soil and Water Conservation, 38(6): 465-467.
- LSU Ag Center. 2000. Sugarcane: Sugarcane Production Best Management Practices (BMPs). Publication 2833: Baton Rouge, Louisiana.
- McCarty, J.L., Justice, C.O., Korontzi, S. 2007. Agricultural burning in the southeastern United States detected by MODIS. Remote Sensing of Environment, 108(2): 151-162.
- McCarty, J.L., Loboda, T., Trigg, S. 2008. A hybrid remote sensing approach to quantifying crop residue burning in the United States. Applied Engineering in Agriculture, 24: 515-527.
- McCarty, J.L., Korontzi, S., Jutice, C.O., and T. Loboda. 2009. The spatial and temporal distribution of crop residue burning in the contiguous United States. Science of the Total Environment, 407 (21): 5701-5712.
- ODA (2007) Oregon Department of Agriculture Natural Resources Division: Smoke Management Program Specifics. Online: http://oregon.gov/ODA/NRD/smokeindex.shtml. Accessed: January 2008.
- SAFE. 2007. Safe Air for Everyone (SAFE) News on Federal Court Decision. Online: http://www.safeairforeveryone.com/docs/fedcourtdec.pdf. Accessed: January 2008.
- USDA/NRCS (2003) USDA Natural Resources Conservation Service (NRCS) 2001 Annual Natural Resources Inventory (NRI): Land Use. Online: http://www.nrcs.usda.gov/technical/land/nri01/landuse.pdf. Accessed: January 2006.
- WA DOE. 2005. Washington Department of Ecology Report: A Look at Agricultural and Outdoor Burning - 2005. Online: http://www.ecy.wa.gov/pubs/0802010.pdf. Accessed: July 2007.
- Wedin, D. 1973. Externalities and open field burning: a case study. American Journal of Agricultural Economics, 55(5): 1026-1029.
- Wulfhorst, J.D., Van Tassell, L., Johnson, B., Holman, J., Thill, D. 2006. An industry amidst conflict and change: practices and perceptions of Idaho's bluegrass seed producers. RES-165. Moscow, Idaho: University of Idaho College of Agricultural and Life Sciences. Online: http://info.ag.uidaho.edu/PDF/RES/RES0165.pdf. Accessed: January 2009.