Farmers Fight Global Warming with No-Till Farming

On one field, there is only rich, lumpy black earth, free of weeds or debris, below the rows of cornstalks waving gently in the breeze. On another field, you can hardly even see the dirt below a thick layer of woody residue -- dried-up bits of corn cobs, pieces of stalk up to eight inches long, even the crumbly remains of the soybean plants that typically alternate with corn crops on Midwestern fields.

A city dweller might think the difference is the matter of a lazy or preoccupied farmer. But in reality, the messier-looking field is an example of a practice that could play a significant role in reducing global warming.

The first field is tilled with a standard plow, a massive machine towed by a tractor that grabs the earth and turns it over completely, removing the residue of past crops. The second field is a "no-till" plot, meaning it was not plowed but rather the new crop was planted amidst the waste of the old. There are also "partial till" plots, in which a special plow that turns over the soil to a lesser degree than the standard one is used.

When a field is plowed, the turning over and stirring of the soil spurs the release of carbon dioxide, which has been identified as a greenhouse gas contributing to global warming and climate change. Though industry and automobiles are responsible for the majority of carbon dioxide emissions in the U.S., the decomposition of organic matter on farmlands is a significant source of the gas. When a field is not tilled, the decomposition and resultant release of carbon dioxide is vastly slowed.

To Till or Not to Till

No-till farming has grown in popularity over the past decade, as farmers who once would have called the practice "crazy" realize the benefits in lower labor and equipment costs and increased productivity. Labor and time are saved when the farmer doesn't plow the field, and the organic matter sitting on the soil works effectively to decrease water run-off and erosion and boost the soil's nutrient retention. In 2000, about 52 million acres in the U.S. were no-till, according to the group Conservation for Agriculture's Future, for a total of about 17 percent of the country's farmland. The practice had increased dramatically between 1990 and 1995, then leveled off over the past half decade.

It wasn't until recently, however, that farmers and scientists began talking about the role of carbon sequestration (meaning 'no-till' or reduction of plowing) in connection with diminishing the greenhouse effect.

A groundbreaking $15 million project called CASMGS (Consortium for Agricultural Soils Mitigation of Greenhouse Gases) being carried out by 10 universities with funding from the U.S. Department of Agriculture is in the process of documenting the environmental benefits of carbon sequestration in agriculture and developing outreach programs to convince farmers to adopt the practice. CASMGS scientists note that while carbon sequestration doesn't actually remove carbon dioxide from the air, it can significantly slow the expected increase in emissions. If no-till farming were widely adopted in the U.S., they say the projected increase in U.S. carbon dioxide emissions could be cut by as much as 20 percent.

"Plants trap carbon during photosynthesis, and that carbon goes into the soil [in the form of plant residue] during harvesting," said Ron Turco, director of the Environmental Sciences Engineering Institute and head of the CASMGS group at Purdue University in Indiana. "We want to keep that carbon in the soil rather than releasing it into the atmosphere as carbon dioxide."

Turco noted that the original carbon content of the soil across the country has been reduced by about 50 percent since John Deere invented the steel plow in the mid-1800s. With widespread no-till, he thinks close to original levels could be restored in as little as 40 years, with 75 to 200 million metric tons of carbon sequestered per year.