Organic farming builds soil organic matter better than conventional no-till farming
Research carried out over 9 years by the US Department of Agriculture’s Agricultural Research Service has shown that organic farming can build soil organic matter better than conventional no-till farming. Organic farming’s addition of organic matter in manure and cover crops more than offset losses from tillage.
In addition, a follow-up three-year study showed that organic plots had more carbon and nitrogen and yielded 18 percent more than conventional no-till plots.
No-till farming is also widely practiced in conjunction with herbicide resistant genetically modified crops, whereby herbicides such as glyphosate are applied on the crops, rather than tilling, to deal with weeds.
However, worries about weed problems in organic farming were allayed by research demonstrating that adding more kinds of crops to the organic rotation helped control weeds. Rotating diverse crops markedly lowers the numbers of weed seeds lying dormant in soil.
Organic Farming Beats No-Till?
By Don Comis
Organic farming can build up soil organic matter better than conventional no-till farming can, according to a long-term study by Agricultural Research Service (ARS) scientists.
Researchers made this discovery during a nine-year study at the Henry A. Wallace Beltsville Agricultural Research Center (BARC), Beltsville, Md. BARC is operated by ARS, the U.S. Department of Agriculture's chief scientific research agency.
Plant physiologist John Teasdale, with the ARS Sustainable Agricultural Systems Laboratory in Beltsville, was surprised to find that organic farming was a better soil builder than no-till. No-till has always been thought to be the best soil builder because it eliminates plowing and minimizes even light tillage to avoid damaging organic matter and exposing the soil to erosion.
Organic farming, despite its emphasis on building organic matter, was thought to actually endanger soil because it relies on tillage and cultivation - instead of herbicides - to kill weeds.
But Teasdale's study showed that organic farming's addition of organic matter in manure and cover crops more than offset losses from tillage.
From 1994 to 2002, Teasdale compared light-tillage organic corn, soybean and wheat with the same crops grown with no-till plus pesticides and synthetic fertilizers.
In a follow-up three-year study, Teasdale grew corn with no-till practices on all plots to see which ones had the most-productive soils. He found that the organic plots had more carbon and nitrogen and yielded 18 percent more corn than the other plots did.
Read more about the research in the July 2007 issue of Agricultural Research magazine
No Shortcuts in Checking Soil Health
experiments are a feature of many ARS
research efforts. Whether in the Pacific Northwest, Midwest, or Southeastern
regions of the
relatively new long-term experiment at
“It is one of a few long-term studies comparing organic farming with no-till,” says John Teasdale, the lead scientist for the 9-year study. “Most others compare organic with conventional plow-tillage cropping systems.” Teasdale heads the Agricultural Research Service’s Sustainable Agricultural Systems Laboratory at Beltsville.
These results are the latest from several long-term projects that are part of ARS’s national program in Agricultural System Competitiveness and Sustainability. This program supports production systems that enhance both profits and natural-resource quality.
Organic Builds Soil Better Than No-Till
From 1994 to 2002, Teasdale compared minimal-tillage organic corn, soybean, and wheat with the same crops grown conventionally with no-till.
Many agriculturalists believe that no-till builds soil better than organic farming, which uses tillage to incorporate manure and control weeds. Tillage is known to destroy soil organic matter. But Teasdale’s study showed that organic farming built up soil better than conventional no-till because use of manure and cover crops more than offsets losses from tillage.
In a 3-year study following the 9-year system comparison, Teasdale grew corn with conventional no-till practices on all plots to see which ones had the most productive soils.
Those turned out to be the organic plots. They had more carbon and nitrogen and yielded 18 percent more corn than the other plots did.
“It takes time for organic matter to build up, so we wouldn’t have seen these surprising results had we only looked after a few years,” Teasdale says.
What About Weeds?
Despite organic farming’s enrichment of the soil, weed problems during the 9-year study were enough to lower corn and soybean—but not wheat—yields below those of no-till crops.
But in another long-term experiment begun in 1996, Teasdale learned that adding more kinds of crops to the organic rotation helped control weeds.
“Weeds tend to adapt to crops whose growth timetable creates conditions favorable to weed growth,” Teasdale says.
Planting the same summer annual crop year after year allows weeds suited to that growth cycle to keep maturing and adding their seeds to the soil. In organic systems, Teasdale showed that rotating diverse crops markedly lowers the numbers of weed seeds lying dormant in soil.
In an ongoing experiment called the “Farming Systems Project,” Teasdale and ARS soil scientist Michel Cavigelli showed that after 10 years, corn yields were higher in diverse organic rotations that included a perennial legume.
“This is one of a few studies that consider the effects of rotation length and crop complexity on organic grain yields,” Teasdale says.
Sustainable Surprises in Grass Seed Country
have also come in recently from the grass seed-growing region of the
in wet western
In a 10-year study, scientists at the ARS Forage Seed and Cereal Research Unit at Corvallis—plant physiologists Gary M. Banowetz and Stephen Griffith, agronomist George W. Mueller-Warrant, and hydrologist Jerry Whittaker—found that rather than burn or bale leftover grass straw after harvest, farmers would do better to plant the next crop right through the straw.
can lead to higher yields and lower costs while also protecting soil
from erosion,” Banowetz says. The study was conducted jointly with
The team also found that no-till meadowfoam—a native winter annual—was a good addition to perennial grass rotations. “It is very suitable to no-till and low-input production. It didn’t need spring fertilizer or herbicide and yielded more seed oil than meadowfoam grown with tillage,” Mueller-Warrant says.
Mueller-Warrant and colleagues also found that meadowfoam and some other rotation crops help to control small rodents called “voles” without the need for tillage to disrupt their tunnels.
In 2006, Washington State University (WSU) and ARS scientists published a paper on an 8-year study on the wheat farm of Ron Jirava. The farm is in an area that has annual rainfall of 11 inches.
paper provides the first comprehensive, multidisciplinary report of
long-term alternative annual no-till cropping systems in the low-precipitation
region of the
In that study, Douglas Young, WSU agricultural economist, found that, in years of normal precipitation, returns from growing no-till spring wheat every year were similar to returns from growing one crop of winter wheat every other year with a year of fallow in between.
In dry years, however, the annual spring wheat showed significantly more economic risk. This made the 8-year average net returns for the annual cropping lag behind the conventional summer fallow rotation by $24 to $29 per acre.
Kennedy appreciates ARS’s ability to sustain research experiments for the long haul—especially collaborative research with university colleagues when grants may run out.
“We often find things that we wouldn’t have found in a shorter study,” she says. “This is especially true in farming, where there are so many variables, such as the weather. Even economic studies require a span of years to get a clear view of what’s really happening. We need to go through enough cycles to average things out.”—By Don Comis, Agricultural Research Service Information Staff.
This research is part of Agricultural System Competitiveness and Sustainability, an ARS national program (#216) described on the World Wide Web at www.nps.ars.usda.gov.
Gary Banowetz, Stephen Griffith, George Mueller-Warrant, and Jerry Whittaker are with the USDA-ARS Forage Seed and Cereal Research Unit, 3450 SW Campus Way, Corvallis, OR 97331; phone (541) 738-4125, fax (541) 738-4160.
Ann C. Kennedy is with the USDA-ARS Land Management and Water Conservation Research Unit, Johnson Hall, Room 215, WSU, Pullman, WA 99164-6421; phone (509) 335-1554, fax (509) 335-3842.