
Farmers Now Part of the Global Warming
Solution as U.S. Agriculture Becomes Net Carbon SinkBy Don Comis May 17, 1999WASHINGTON, May 17,
1999--Sometime in the past 15 years, American farmers turned an
environmental corner, Agricultural Research
Service Administrator Floyd Horn announced today. A dramatic change in tillage techniques shifted U.S. farm soils from
net carbon dioxide producers to net accumulators of carbon--in the form of
valuable soil organic matter. This makes their soils more productive and part
of the potential global warming solution, rather than part of the
problem, Horn said. American farmers have virtually abandoned the
moldboard plow used to break open the American West. Horn said that Raymond R. Allmaras, a soil scientist with the
U.S. Department of Agricultures
Agricultural Research Service in St. Paul, Minn., made these findings after a
thorough search of published reports and surveys for several major crops,
comparing 1940 to 1990 conditions. These reports showed that, in 1980, 75 to 85 percent of American
farmers were still using the plow. By 1993, a USDA survey showed that farmers
used the moldboard plow on only 6 to 9 percent of corn, soybean, and wheat
fields, Horn said. Horn said Allmaras used yield records to estimate amounts of crop parts that
would be left after harvest. He also used long-term tillage experiments
conducted by himself and ARS colleagues nationwide. Dale E. Wilkins, an ARS
agricultural engineer in Pendleton, Oregon, assisted him in
the study, Horn said. Allmaras said that one of his tillage experiments showed there was no carbon
accumulation in soils during a 10-year period when corn and soybeans were
planted after annual plowing; another showed that abandoning the moldboard plow
produced distinct increases in soil carbon in as little as 10 years. The soil is storing more carbon that otherwise might be in the
atmosphere as carbon dioxide, which is one of the greenhouse gases thought to
cause global warming, Allmaras said. The plow lifts and inverts an
8 to 12-inch slice of soil, and also buries stubble and other unharvested crop
residue that was once on or near the surface. That places the residue deep in
the plow layer where different microbes live. These microbes convert the
residue to a form of carbon that readily converts to CO2, which can escape to
the atmosphere, he said. As farmers put aside the plow, they leave more residue on the soil or within
a depth of 4 inches, Allmaras said. For example, corn and grain sorghum
farmers are returning about twice as much residue than in 1940, and they are
keeping it on or near the surface. Here, the residue readily decays to valuable
organic matter, a more stable carbon compound and a key component of the black,
fertile prairie soil originally broken open by the plow. The moldboard plow
robbed the soils of the increased organic matter offered by the yield increases
since 1940, Allmaras said. Allmaras said the dramatic shift away from the moldboard plow has altered
the farm landscape in another equally broad way: the reduced tillage and
increased organic matter in the soil has led to a looser, less erodible soil
that holds more water for crops. This noticeable shift in the soil is the
main reason farmers have abandoned the moldboard plow, he said. Horn added that farmers too often are criticized for causing environmental
problems. Heres a case where theyre definitely part of the
solution, and for that, they deserve a pat on the back, he said. Scientific contact: Raymond R. Allmaras, ARS
Soil and
Water Management Research Unit, St. Paul, MN, phone (617) 625-1742,
[email protected]. U.S. Department of Agriculture | |