On the Central Great
PlainsFallowing Falls by the Wayside
Planting foxtail millet, a summer annual forage with low water needs, helps
conserve water for subsequent crops.
An aerial view of the Central Great Plains' amber waves of grain shows they
are changing dramatically.
Land once left bare every other year is now a quilt of yellows, golds, and
earth tones. Since 1990, corn and sunflower acres have increased from few or
none to about 140,000. Since 1980, proso millet acres have tripled to 600,000.
The Central Great Plains area comprises about 20 million acres of dryland
farms in parts of Colorado, Wyoming, South Dakota, Nebraska, and Kansas.
Farmers and ranchers there are paying more attention to recent agricultural
research that has proven that a systems approach based on ecological trends in
and on the soil may enable them to drastically limit their use of
fallowthat is, leaving the soil bare.
Switching to this holistic approach could improve the rural economy across
the region by making farming a more sustainable venture over the long haul.
Rainfall on the Central Great Plains averages a mere 14 to 18 inches a year,
so growers traditionally alternate a year of rainfed crops with a year of
fallow. Precipitation stored in the soil during the fallow year can slake the
thirst of the following year's wheat or other crop.
But scientists with the Agricultural
Research Service are showing that ecologically based farming practices can
provide for crops' water needs with less need for fallow.
"We've improved water use so well, we're nearing our goal of a crop
every year," says agronomist Randy L. Anderson, who is at ARS' Central
Great Plains Research Station in Akron, Colorado.
To see how a crop rotation sequence affects corn growth, biological technician
Karen Couch will measure the leaf area of growing plants.
Three Decisive Factors
Reaching this crop-every-year goal is not simple or guaranteed, cautions
Akron soil chemist Rudy A. Bowman. "Based on long-term trends, we have
observed that three factors are needed before we see soil system changes: soil
surface cover with residue, continuous cropping, and no tillage."
What system changes can occur if all three factors are present? "For
one thing, we have found that more phosphorus will be available for
crops," Bowman says.
Adds biophysicist Robert M. Aiken, "Also, with continuous cropping,
organic matter levels in the top 2 inches of soil are 20 percent higher than
with wheat-fallow. If the rotation includes fallow, organic matter does not
increase." Formerly with ARS, Aiken works at the Kansas State University
Experiment Station at Colby.
"We have always recognized that fallow leads to soil erosion and
strains farmers' economic resources, since they only get one crop every 2
years," Aiken says. "Now, we can minimize fallow if we design
rotations with appropriate crop sequencing."
Team Approach to Solving Problems
The Akron teamBowman, Anderson, Merle F. Virgil, Joe G. Benjamin, and
David C. Nielsenhas been evaluating new crop sequences since 1990. They
pool their expertise in weed science, soil physics, soil health, meteorology,
soil fertility, and organic matter to gain insights into biological responses
of crops, weeds, soils, insects, and soil microbes to crop sequencing.
The Akron team screened more than 20 dryland crop rotation and tillage
systems to find the best combinations. Then they compared these rotations to
"In the Central Great Plains, farmers' biggest natural obstacle is not
having enough water to grow crops continuously," says Nielsen, an
agronomist. "That's why they have traditionally left their land bare every
"However, we've found that those wheat-fallow systems use only 40
percent of the average annual rainfall. With continuous cropping, water use
approaches 80 percent."
Still, Anderson notes, "producers have to be careful how they sequence
crops to avoid crop failure for lack of water. We've found that by using a
cycle of four crops, alternating high- and low-water-use crops, they can
successfully crop continuously in years with normal or higher
precipitation." For example, continuous cropping with wheat-corn-proso
millet in rotation doubles the land's productivity, compared to the traditional
And in dry years? "We still have to work at rotations that succeed in
dry years," admits Virgil, a soil scientist. "One option we're
exploring is to include forage crops or green fallow. Both use less water than
the current cropswheat, corn, millet, and sunflowers."
The team discovered that crop sequencing can sometimes increase yields.
"For example," says Anderson, "we found that corn is beneficial
to a following crop of proso millet or sunflower." And they found that a
broadleaf crop like sunflower also improves yields of the following crop.
Agronomist Randy Anderson (left), soil scientist Merle Vigil (center), and soil
chemist Rudy Bowman look for symptoms of disease on corn roots. Varied crop
rotations can minimize its occurrence.
But sunflowers yielded most when grown only once every 4 years, the team
found. "More frequent cropping than this favored the buildup of soilborne
diseases," says Benjamin, a soil physicist.
Wheat, corn, and proso millet yields were also higher with a longer interval
The scientists are investigating reasons for these yield increases.
"They may be due to changes in soil microbe communities, such as increases
in mycorrhizae when corn is grown," says Bowman.
These results led the scientists to develop rotations based on the 4-year
cycle. "By diversifying crops in the rotation," says Bowman,
"the farmer encourages more diverse soil microflora. And soils with a
diversity of microorganisms have a natural antagonism to soilborne crop
diseases." In the end, the diversity of crops and microbial populations
makes the ecosystem more sustainable over the long haul.
This notion of diversity extends even to crop roots. The team found that
rooting depth and types of roots of crops can vary considerablyeven
within the same field.
"Farmers can take advantage of these differences to grow the best crops
for the soil and environmental conditions," says Aiken. "They can
plan rotations to improve root health so roots explore a greater volume and
depth of soil. This improves the overall efficiency of roots in taking up
fertilizer at various soil depths."
The cycle of four cropstwo winter crops followed by two summer
cropsalso minimizes weed densities, says Anderson. This approach may help
growers reduce pesticide use and subsequently production costs.
"The wheat-fallow system strains farmers' economic resources because
its high cost exceeds the income derived from it. Government payments now
subsidize the low-income wheat-fallow system. With the end of government
payments in 2002, this system will be a financial loser," says Colorado
State University economist Dennis A. Kaan, who works at Akron with the team.
"We've found that alternative rotations can be 20 to 40 percent more
profitableespecially if they include corn or sunflowers," Kaan says.
"Both crops are high water users, so our goal is to understand how they
can be sequenced with low-water-use crops to ensure that we do not exceed our
water limits."By Hank
Becker, Agricultural Research Service Information Staff.
This research is part of Soil Resource Management, an ARS National
Program (#202) described on the World Wide Web at
Randy L. Anderson and
other ARS scientists mentioned in this article are at the USDA-ARS
Central Great Plains Research
Station, 40335 County Rd. GG, Akron, CO 80720; phone (970) 345-2259, fax