Group Title: Agricultural research (Washington, D.C.)
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Title: Agricultural research
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United States -- Agricultural Research Service
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U.S. Department of Agriculture Agricultural Research Service .J y 199
Agricultural Research



What Will It Do to

Climate has changed tremendously
over geologic time. Even during the rela-
tively stable climate since the last ice age
ended about 12,000 years ago, conditions
have varied-sometimes for more than a
century at a time-from much cooler and
wetter to very warm and dry.
So there is nothing new about climate
change. What does appear to be different
is the possibility of a new cause of
climate change. Now, human influence
on natural processes and cycles may
affect the range of temperatures near the
Earth's surface, amounts and patterns of
precipitation, and other important aspects
of weather, like the frequency and
severity of storms.
The atmosphere contains small
concentrations of carbon dioxide and
other gases that absorb a portion of the
sun's energy as it is radiated back
towards space from the Earth. This
greenhouse effect warms the lower
atmosphere and planet surface. Scientists
have shown that concentrations of so-
called greenhouse gases have increased
dramatically since the beginning of the
Industrial Age about 200 years ago, as a
direct result of human activities-and
that the concentrations are still rising.
Though scientists are not as certain
about the effects of this change on
climate, some think climate change could
be disastrous and has already begun. A
recent assessment by the United Nations-
based Intergovernmental Panel on
Climate Change concluded that "the
balance of evidence...suggests a discern-
ible human influence on global climate."
The panel's assessment projects a rise in
global mean temperature of about 20C by
the year 2100.
Other scientists do not yet find a
human effect on climate and do not
expect one. Obviously, much remains to
be learned.

And while answers to questions about
changing carbon dioxide levels, temper-
ature, and precipitation patterns are
important to virtually all sectors of the
U.S. economy, they are especially
important to agriculture.
In the United States, fine-tuning
agriculture to match environmental
conditions and to tolerate highly variable
weather has allowed us to provide the
best quality and greatest diversity of
food ever known-and at reasonable
prices. This bounty could be threatened
if rising temperatures and altered rainfall
patterns catch us unprepared.
For that reason, the Agricultural
Research Service (ARS) has taken an
active role in providing research results
that are helping scientists predict how
crop and animal production systems and
agroecosystems will respond to change.
This issue of Agricultural Research
presents a wide sampling of ARS studies
and results that are directly applicable to
the subject of climate change. Included
is basic science about how plants
respond at the biochemical level to
temperature and drought stresses. We're
developing crop varieties that better
withstand heat and drought, and we're
improving predictions of possible
climate change effects on water supplies.
Our investigations of agriculture's
contributions to greenhouse gas emis-
sions show how management and
conservation practices reduce those
emissions and how agriculture can help
reduce total global emissions.
Such information is necessary for
making informed decisions and formu-
lating appropriate policies. The feature
article on page 4, "Preparing Agriculture
for a Changing World," is especially
timely, because environmental ministers
from over 160 nations are meeting
periodically to negotiate an international
agreement to decrease emissions of
greenhouse gases.
Of course, ARS researchers do not
work alone in addressing global issues.
We are but one agency in the United

States Global Change Research Pro-
gram-established by the Global Change
Research Act of 1990-and are part of
an even larger international community
of scientists. Information about the U.S.
program is available on the World Wide
Web at
In addition, the ARS National
Agricultural Library provides research
and educational institutions access to one
of the world's most extensive collections
of data on both agricultural and natural
ecosystems. Their challenge is to help us
integrate and apply that knowledge to
understanding global change, since much
of the information was collected to
support other agricultural research
programs and objectives.
Climate change is only one aspect of
environmental change that may affect the
entire world. Global environmental
change, commonly called global change,
refers to large-scale changes-whether
of natural or human origin-in Earth's
biological, geological, hydrological, and
atmospheric systems.
Other examples of global change
include the direct effects of rising carbon
dioxide levels on plants and ecosystem
processes, depletion of the stratospheric
ozone layer that filters out harmful
radiation, declining biological diversity,
and processes like deforestation and
desertification that threaten the natural
resources that sustain us.
These, too, are issues that require our
attention now, because they may limit
our options in the future. And to the
extent that agriculture contributes to, is
affected by, or can mitigate these
changes, ARS scientists will continue to
search for knowledge and solutions.

Herman S. Mayeux
ARS National Program Leader
for Global Change

Agricultural Research/July 1997

July 1997
Vol. 45, No. 7
ISSN 0002-161X

Agricultural Research is published monthly by
the %gncultural Research Service, U.S.
Department of Agriculture, Washington, DC
The Secretary of Agriculture has determined
that this periodical is necessary in the transac-
tion of public business required by law.
Dan Glickman, Secretary
U.S. Department of Agriculture
Catherine Woteki, Acting Under Secretary
Research, Education, and Economics
Floyd P. Horn, Administrator
Agricultural Research Service
Robert W. Norton, Director
Information Staff
Editor: Lloyd McLaughlin (301) 344-2514
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Agricultural Research

Preparing Agriculture for a Changing World 4

RZWQM-Modeling Effects of Farm Decisions 18

Mending the Ties That Bind 20

String Trimmers for Curbing Weeds in Row Crops 21

New Clues to Wheat Hardness 21

Dogwood, Hydrangea Chemicals Foil Key Crop Pests 22

Fuzzy Leaves Confuse Fungi 22

Science Update 23

Aericu'~Atua1ResearcYNJuiy 'l997

'. re

f`. *:'.'

,. "~'c-
i .

release carbon dioxide
(CO2) into the atmo-
sphere. In the wondrous
biological process of photosynthesis,
plants use the sun's energy to
convert this gas to the food we eat
and the oxygen we breathe.
Yet this crucial gas may have a
dark side. C02 and some other gases
may be changing our climate.
Atmospheric C02 concentrations
have risen from 280 to more than
350 parts per million during the last
200 years. At current C02 emission
rates, that concentration will double
again over the next century.
"The so-called greenhouse effect
is a natural process that helps keep
the planet surface at a comfortable
temperature," says Herman S.
Mayeux. "The concern is that
concentrations of greenhouse gases
are increasing in the atmosphere. As
a result, the surface temperature of
the planet may be rising." Mayeux is
the ARS national program leader for
rangelands and global change at
Beltsville, Maryland.
Potential temperature increases
and the changes in precipitation
patterns that could occur because of
the rise of greenhouse gas concen-
trations are known collectively as
global climate change.
Scientists can measure an in-
crease in atmospheric gas concentra-
tions, but determining the effect of
that rise is difficult because of
natural variability in temperature
and precipitation. Computer models
that simulate atmospheric behavior
indicate that global temperatures
generally increase as greenhouse gas
concentrations rise.
"Because climate and C02 play
such important roles in agriculture,
any long-term changes are of great
concern," Mayeux says.
For that reason, ARS scientists
nationwide are evaluating U.S.

PERRY RECH (K3829-14)


w..i .World

Range scientist Herman Mayeux checks a light-sensing bar that indicates solar radiation
levels within plastic growth tunnels. Carbon dioxide concentrations inside the tunnels
range from today's 350 parts per million to the 200 ppm present during the last ice age.

agriculture's contribution to the
increase in greenhouse gases, the
potential impact of climate change on
how we produce food, and the
industry's unique opportunities to
help mitigate atmospheric change.
The following pages present a
glimpse into the variety of state-of-
the-art experiments under way in
ARS. The projects range from basic
studies that provide a foundation for
our understanding of how plants
interact with the atmosphere to
applied research on the impact of
specific farming techniques.

All of the work shares the goal of
reducing uncertainty about how
global climate change will affect
agriculture and future food security.
Information on how to contact each
of the ARS scientists mentioned in
these stories begins on page 16.

Agriculture's Contribution to
Global Change
Scientists use the term "climate
forcing" to compare the contribution
of different activities to climate
change. Climate forcing is a measure
combining estimates of greenhouse

Agricultural Research/July 1997


gas emissions with the absorption of
long-wave radiation from the Earth
and the estimated lifetime of each gas
in the atmosphere.
U.S. agriculture is responsible for
less than 1 percent of this forcing,
according to the Council for Agricul-
tural Science and Technology, a
nonprofit agricultural sciences
organization based in Ames, Iowa.
Agriculture and industry contribute in
various ways to atmospheric concen-
trations of three greenhouse gases.
Carbon dioxide-Microbes
produce C02 in soil as they free up

The Greenhouse Effect

Solar radiation passes though the atmosphere and warms the Earth's
surface. Some is reflected back into the atmosphere and dissipates into
space. The greenhouse effect refers to an accumulation of specific
gases that absorb the reflected radiation, effectively trapping heat in
the lower atmosphere. The most important of these gases are water
vapor and CO2. Smaller amounts of methane, nitrous oxide, chlorof-
luorocarbons. and ozone also contribute, intensifying the greenhouse
effect. But global \\arming doesn't mean e\er. place on Earth will be
%warmer. Rather, it indicates a general rise in the planet's average
surface temperature. More important than either the rise in gases or
temperature would be the potential impacts of these increases-
changes in the amount and pattern of rain and snow fall, length of
growing seasons, sea le\el, and storm patterns.

The chart below shows how concentrations of three greenhouse gases
changed between 1800 and 1990.

Gas Atmospheric concentration Current rate of
change per year

circa 1800 1990

Carbon dioxide

280 ppmv*

353 ppmv

1.8 ppmv

Methane 0.8 ppmv 1.72 ppmv 0.01 ppmv.

Agricultural Research/July 1997

carbon molecules while feeding on
organic matter. Tillage not only frees
CO2 in bursts of gas, but also lets in
oxygen that speeds up microbial
action. Crops and other plants reduce
atmospheric C02 levels as they take it
from the air during photosynthesis.
Burning forests and grasslands are
other sources. But burning fossil fuels
like oil, coal, and gas accounts for
most of the world's CO2 emissions.
Methane-This gas is released
from many sources, including gas
drilling areas, coal mines, landfills,
natural water bodies like oceans and
lakes, holding ponds for animal
waste, and rice paddies. Methane is
also produced by the digestive
processes of ruminant animals and
termites. Some bacteria in soils
produce methane, while others
transform it to other compounds,
effectively removing it from the
Nitrous oxide-The synthetic
form of N20 is the "laughing gas"
used by dentists as an anesthetic.
Agricultural and natural processes
within soils, burning of vegetation
and fossil fuels, and the oceans all
appear to release N20. On farmland,
microbes emit it as they feed on
nitrogen fertilizers and manure.
Fertilization with nitrogen increases
emissions of N20 from cropland and
pasture soils.

Climate Change and Basic
Understanding climate change on a
global scale means getting up close
and personal with a single plant-or
even with a single cell in a plant.
"Nature has a way of rewarding
those who take the time to look
closely at basic processes," says
Steven J. Britz, an ARS plant physi-
ologist at Beltsville.
Agency scientists around the coun-
try are examining how elevated atmo-


Photosynthesis taking place in wheat plants can be measured in field chambers like this
one being adjusted by plant physiologist Richard Garcia.

spheric CO2 and other greenhouse
gases affect three essential biological
processes: respiration, or the ex-
change of oxygen for C02; the use of
light in photosynthesis to remove C02
from the air for plant growth and re-
production; and water use.
Research to date both confirms
some long-held beliefs about plant
response to elevated C02 and adds to
what we already know.
For example, elevated levels affect
a plant's respiration. James A. Bunce,
an ARS plant physiologist at Belts-
ville, grew soybean plants in CO2
chambers at nearly double the current
atmospheric level. Surprisingly, while
higher levels of C02 increased plant
growth, they lowered plant respiration.
"We expected the plants to have a
higher rate of respiration," says Bunce.
"It's still a mystery how the rate of res-
piration can be reduced without a neg-
ative impact on the plant."
Other studies show that changes in
the atmosphere affect how plants use
water. Like scientists at other ARS
laboratories, Bunce and colleagues

found that plant water use changes
dramatically when the plants grow in
higher atmospheric C02.
By studying the plant stomata-
the pores on the leaf surface that
regulate water loss from the leaf-

To determine how elevated C02 may
reduce water use by crops, plant
physiologist James Bunce measures water
vapor conductance of barley leaves grown
at twice the current atmospheric C02

\ \

they found that at higher C02 levels,
plants use less water to produce the
same amount of growth. This re-
sponse is commonly seen in the
growth chamber and greenhouse, but
the overall reduction in water use for
crops grown in the field seems to be
less than 5 percent, for reasons that
are not yet understood.
ARS soil scientist Bruce A.
Kimball and colleagues at Phoenix,
Arizona, confirmed that plant
photosynthesis is immediately
stimulated when you double the
atmospheric CO2. He also showed it
doesn't necessarily slow down over
time in crops such as wheat and
cotton or fruit trees like oranges. In
experiments with sour orange trees,
Citrus aurantium, physicist Sher-
wood B. Idso observed sustained
explosive growth over a 9-year
period when the trees grew outdoors
under experimentally elevated CO2.
Scientists speculate that this level
of response to increased CO2 concen-
trations will lead to an overall net
increase in productivity in many
Other greenhouse gases can add to
this effect. For example, ARS plant
physiologist Joseph E. Miller and co-
workers at Raleigh, North Carolina,
found that the atmospheric concen-
tration of ozone near ground level
affected the degree to which elevated
atmospheric C02 stimulated photo-
synthesis in soybean leaves. Under
today's CO2 concentrations, ozone
can suppress photosynthesis, but
Miller's experiments showed that
photosynthesis and yield were
increased more by elevated CO2 if
plants were stressed by ozone.
"This is one example of the
complexities involved in understand-
ing how plants will respond to global
environmental change," Miller says.
"Clearly, we have a lot to learn about
how the different contributors to
climate change interact-and how

Technician Stephanie Johnson measures
the rate of photosynthesis in leaves of an
orange tree growing in a C02-enriched

those interactions will affect plant

The FACE Project
The Free Air C02 Enrichment
project (FACE) in Arizona is helping
scientists from around the world to
understand how plants respond to
actual field conditions representing
those anticipated in the next 50 to 75
years. Large amounts of CO2 are
vented through upright pipes that
maintain a constant CO2 concentra-
tion of 550 parts per million in the
atmosphere around the plants.
"Our FACE project, begun in
1989, is the longest running of five
now providing researchers with
information needed to assess impacts
of global change," says Kimball.
"We have studied cotton and wheat,
while the other experiments concen-
trate on forage grasses, loblolly pine,
chaparral, and desert plants." In
general, Kimball's work has shown
that crop yields increase as C02

[For more details on FACE, see
"FACE-ing the Future," Agricultural
Research, April 1995, pp. 4-7.]

Tillage Releases Carbon Dioxide
Decades of tillage have caused
soils on American cropland to lose up
to half their virgin organic matter.
Much of it may literally be going up
in a puff of gas-as CO2.
"Carbon is the backbone of the
organic matter that made our native
prairie soils so black and fertile,"
says Donald C. Reicosky, an ARS
soil scientist in Morris, Minnesota.
"Soil carbon levels have been declin-
ing ever since the first plows tore up
prairie land."
The worst of the short-term losses
occurs within minutes after the
moldboard plow fractures the soil,
forcefully releasing C02 stored in
soil pores and water. "It's just like
opening a bottle of champagne. The
gas in the air space above the liquid
is released, and C02 bubbles out of
solution to establish a new equilib-
rium in the air," he says.
"The C02 is a byproduct of
microbial feeding on, and the biologi-
cal oxidation of, soil organic matter,"
says Reicosky, who has measured
CO2 losses from soils in Alabama,
Texas, and Minnesota. He gauges the
amounts with a clear, plastic chamber
equipped with an infrared C02
analyzer and carried by a tractor.
Studies by Reicosky and col-
leagues show that the soil releases as
much as 260 pounds of C02 per acre
per hour immediately after tillage.
Over time, even more is lost because
of the extra oxygen let in by tillage
and the extra organic matter from
crop residues plowed under. "That
speeds up decomposition," notes
Reicosky. "You're able to feed more
soil microorganisms faster, and there
goes your organic matter."

Agricultural Research/July 1997

Not coincidentally, as the amount
of soil carbon has declined, atmo-
spheric CO2 has gone up. The inten-
sive tillage seen in America's post-
World War II farming boom in-
creased the rate at which soil carbon
was converted into C02, just as the
Industrial Age's coal-burning smoke-
stacks were turning coal carbon into
C02 at a furious pace.
But if tillage is the cause, it's also
the cure, Reicosky says. Crop residue
management and conservation tillage
reduced carbon losses by up to four-
fifths in Reicosky's studies. These
practices disturb the soil less and
conserve organic matter by leaving
dead roots undisturbed and crop
residue on the surface after harvest.
"The trick is to use crop residue
management and other soil manage-
ment techniques to keep carbon where
it belongs," he says. "Let the soil
serve as a storage reservoir, or sink,
for excess carbon created from human
activity, ameliorating the potential en-
vironmental harm of rising levels of
atmospheric carbon dioxide."
There are estimates that wide-
spread adoption of improved crop
residue management could return soil
carbon levels to near those of our
native prairies, storing or sequester-
ing a portion of the carbon released
through worldwide fossil fuel emis-
sions, Reicosky says.
Of course, returning highly erod-
ible cropland to perennial grasses
would be even better, says program
leader Mayeux.
"To date, that has been done on 36
million acres (15 million hectares) of
land taken out of production and
covered with grass or trees under the
federal Conservation Reserve Pro-
gram," he says.
"Each year, these CRP soils may
be storing almost a third of the 38
million metric tons of carbon released
annually into the atmosphere by all
sources related to U.S. agriculture.

Most of these lands are dryland farms
in the Great Plains."

Animal Waste Gives Off Gases
Like Reicosky, Lowry A. Harper,
an ARS agricultural microclimatolo-
gist in Watkinsville, Georgia, also
measures C02-not from soil but
from animal waste treatment ponds
called lagoons.

He has devised a system for
measuring C02 and other greenhouse
gases with an array of outdoor
"sniff," or sampling, tubes connected
to a laser spectrometer or an infrared
gas analyzer.
For the lagoons, Harper mounts
the sniff tubes on a floating barge to
detect C02, methane, nitrous oxide,
and ammonia emissions. Harper's

Agricultural Research/July 1997

YFU UbllMnUn IYE~17-4~

research will not only help computer
modelers better evaluate the green-
house gases emitted from animal
waste lagoons, but also establish
whether there's enough methane
emitted to make it worthwhile for a
farmer to use it as fuel for an electri-
cal generator.
Harper uses a land-based version of
the sniff tubes for measuring methane

emissions from cattle breath. He uses
similar techniques to detect nitrous
oxide on land and has measured
significant emissions where animal
wastes have been spread.
Eventually, he and others plan to
adapt the equipment to measure gas
emissions from soil, landfills, rice
paddies, animal manure, and termite

--i_ ~

Agricultural Research/July 1997

From his tests so far with cattle in
Australia, Georgia, and Texas-the
first such outdoor tests in the
world-Harper has found that a cow
grazing on pasture can emit more
than 8 ounces (230 grams) of meth-
ane per day. "That is somewhat more
than estimates from indoor tests of
confined animals," he says. The
studies also pointed to a solution:
Higher quality diets reduced methane
emissions. Cows fed grain rather than
pasture grass emitted only 2.4 ounces
(70 grams) per day, about half as
much as previous tests indicated.

Modeling the Future
Many people use a computer in
day-to-day activities, be it to get cash
from an automated teller machine or
to compose a letter. But scientists and
engineers first used-and continue to
use-the power of computers to
analyze complex problems like
potential climate change.
Computer models help researchers
get a handle on how environmental
changes might affect plants, animals,
water supplies, and even human
comfort. In the agricultural arena,
these models often go by a strange-
appearing combinations of letters.
Some of these are EPIC, RZWQM,
NLEAP, and SPUR2. [More on
RZWQM on page 18.]
"Historically, ARS has solved
agricultural problems on field,
regional, and sometimes even a
national scale-but not on a global
level, says ARS soil scientist
Ronald F. Follett. "But because we
have decades of research on soil,
water, crops, natural resources, and
other issues that are important to
global change, scientists who run
global models are looking to ARS for
Based in Fort Collins, Colorado,
Follett heads up research that focuses

on the cycling of carbon and key
greenhouse gases between the
atmosphere and land.
From the beginning of ARS'
involvement in the U.S. Global
Change Research Program (see
Forum, p. 2), scientists recognized
the need to develop models of plant
and soil processes and to scale them
up to make regional predictions. The
agency's scientists were well quali-
fied to do this, having developed
models that worked at the field level
for many years.
"ARS researchers nationwide
continue to develop the needed
models," says Basil Acock, an ARS
plant physiologist at Beltsville.
"Many are modular so that each
component can be plugged in or
taken out without affecting the
overall function of the larger model.
This standardization allows research-
ers to borrow various components
developed by others, and it avoids
duplication of effort," he says.
The models will improve estimates
of plant growth and yield, greenhouse
gas emissions and sinks, and water
and energy flows on cropped lands,
forests, and rangelands. Others will
simulate changes expected because of
pests, diseases, and salinity.
The scientists run "what would
happen if..." scenarios over 10- to
100-year periods. That should
provide clues on how to mitigate
global climate change.
"Whatever model we use to predict
change, it must be responsive to all
environmental factors-temperature,
nutrients, water, and more important-
ly, land management," says Jon D.
Hanson, an ARS rangeland scientist
at Fort Collins, Colorado. He devel-
oped SPUR2 (Simulation of Produc-
tion and Utilization of Rangelands),
one of the agency's most complete
models for predicting how climate
change would affect U.S. cattle-
grazing areas. His research suggests

At Fort Collins, Colorado, technicians
Julie Roth and Edward Buenger (photo
below) prepare soil samples and conduct
several types of analyses that will tell
scientists how much carbon plants have
pulled from atmospheric C02 and stored
in soil organic matter.

that the country's best grazing lands
could gradually shift more to the east
and north.
ARS is uniquely equipped to
conduct studies in global change
because it has acquired long-term
hydrology and climate databases,
some covering more than 40 years.
The hydrology data come from
measurements made on large water-
sheds located near Tucson, Arizona;
Tifton, Georgia; Boise, Idaho;
Oxford, Mississippi; Coshocton,
Ohio; El Reno, Oklahoma; Universi-
ty Park, Pennsylvania; and Temple,
Texas. Much of the data is archived
at the ARS Water Data Center, part
of the Hydrology Laboratory at
Beltsville. ARS laboratories in Fort
Collins, Coshocton, El Reno, and
Temple provide the climate data.

Climate's Impact on Snowpacks
Some of the best water on Earth
comes from the melting snowpacks
of high-mountain watersheds in the
western United States. These rugged
basins provide 50 to 80 percent of the
West's water for cities, farms,
ranches, hydroelectric power plants,
and other downstream destinations.
"But even a modest warming or
cooling of our climate," says Keith
R. Cooley, "could change the timing
and amount of snowmelt." He's an
ARS hydrologist at Boise, Idaho.
That's why Cooley and colleagues
are expanding and fine-tuning
computer-based mathematical
models that predict how changes in
the Earth's climate may quicken-or
delay-snowmelt from tomorrow's
snowpacks. Equally as important,
they are working to improve their
estimates of changes in the amount of
runoff that snowpacks of the future
will provide.
Three such models predicted re-
markably similar trends when used to
project changes in timing and yield
from western snowpacks. The study

Agricultural Research/July 1997

SCOTT BAUER (K5060-12)

Am .--- -


* .1..

Global warming predictions indicate the amount and timing of snowmelt and runoff may change in western basins like ARS' Reynolds
Creek Experimental Watershed near Boise, Idaho.

was the first of its kind to encompass
such a diverse assortment of western
watersheds, says Albert Rango, an
ARS hydrologist at Beltsville.
For the experiment, Rango and
Cooley selected seven watersheds
scattered throughout four western
states and Canada. These basins
ranged from sagebrush-clad slopes
that receive an annual average of
about 20 inches of rain or snow to
thick forests of spruce and fir that
receive about 50 inches. The re-
searchers programmed the models to
predict what might happen to snow-
fields if the Earth's atmosphere were
5"F to 90F warmer.
Global warming, the researchers
report, would cause snowmelt and

runoff to start-and to peak-earlier
in the year. "The greatest volume of
runoff could occur not in May or
June, our typical snowmelt months,"
says Cooley, "but instead in March
or April. That means western
farmers of the next century may have
to make new choices when deciding
what kinds of crops to plant."
What's more, the snowpack might
yield less water. "A warmer cli-
mate," explains Cooley, "not only
causes the runoff to occur sooner,
but may also cause less snow to
accumulate at certain elevations.
At the time it was selected for the
seven-basin study, the Snowmelt
Runoff Model, or SRM, that Rango
developed relied primarily on

temperature estimates. Today's SRM
takes into account two other key
factors-radiation and cloud cover.
Rango says a cooperative research
and development agreement between
ARS, the industry-sponsored Electric
Power Research Institute, and the
U.S. Geological Survey funded part
of the work that led to the newer,
more savvy model.

The Carbon Disappearance
More than 7 billion metric tons of
carbon enter the atmosphere in the
form of C02 each year. But when
scientists measure the increase in
C02 concentrations in the air, they

Agricultural Research/July 1997

can only account for about half of the
carbon. Where are the "missing" 3
billion metric tons?
That's about the amount of coal
burned for electricity during a 3- to
4-year period in the United States.
"The answer matters because if
the C02 concentration affects
climate, we can't predict what will
happen in the future until we under-
stand the global carbon cycle," says
Mayeux. "If the Earth's vegetation
and soils are absorbing the CO2
we're releasing, that could forestall
the rate of C02 buildup in the
Some of the missing carbon might
be stored in Nevada's high deserts,
Oklahoma's prairies, or in grasslands
near you.
"Plants take in C02 and convert
the carbon to leaves, stems, roots,
and fruit," says Mayeux. "Since
rangelands cover half the Earth's
land area and contain one-third of the
plant life, they're a logical place to
look for the missing carbon."
ARS scientists at 11 locations
across western rangelands are doing
just that. They're using sophisticated
meteorological instruments called
Bowen ratio/energy balance units to
understand how C02 moves between
the air and vegetation on U.S. range-
lands. The units run continuously on
plots of at least 15 acres each.
Participating ARS locations
include Tucson, Arizona; Fort
Collins, Colorado; Dubois, Idaho;
Miles City, Montana; Las Cruces,
New Mexico; Mandan, North Dako-
ta; Woodward, Oklahoma; Burns,
Oregon; Temple, Texas; Logan,
Utah; and Cheyenne, Wyoming.
Bill Dugas, agricultural meteorol-
ogist at the Texas Agricultural Ex-
periment Station in Temple, is com-
piling the data under a cooperative
agreement with ARS. Tagir Gil-
monov, a visiting Russian ecologist,
is currently working at Logan to help

some of the network participants de-
velop predictive models based on the
CO2 fluxes and weather data.
"If rangelands store excess carbon,
we will find that the amount of
carbon in the plants and soil organic
matter increases over time," says
Phillip L. Sims, a rangeland scientist
at Woodward. So far, ARS research-
ers have learned that the amount of
CO2 absorbed by the vegetation
fluctuates significantly from location
to location and even over short
periods at each site.
"Within 3 years, we'll know what
the fluxes are on undisturbed grass-
lands," says Sims. Many of the
locations are also conducting smaller

scale experiments that compare how
various management strategies affect
the land's ability to store carbon.
ARS researchers in Burns, for
example, designed portable, 1-meter-
square plastic chambers that allow
them to measure C02 exchange
around single plants, rather than over
large areas of rangeland." This tool
lets us conduct small-scale, replicated
experiments," says ARS rangeland
scientist Raymond F. Angell. He's
evaluating the impact of fire on C02
absorption by rangelands.
"Prescribed burning is an effective
way to increase the grass component
of rangelands that have become
dominated by shrubs and trees


Plant physiologists Jack Morgan (left) and Dan LeCain have designed and installed six
open-top chambers at the ARS Central Plains Experimental Range in eastern Colorado.
Three of these greenhouse-like chambers are receiving injections of C02 to simulate
anticipated global concentrations, and three operate under current atmospheric levels.

Agricultural Research/July 1997

because of long-term fire suppres-
sion," Angell says. The controversy
arises because burning releases C02
into the atmosphere. "But we believe
that the increased growth right after
the burn may take up more CO2 than
is released," he says.
Angell and colleagues are now
measuring baseline conditions on the
study sites. Then they'll burn some of
the plots and use the chambers to
measure changes in CO2 uptake as the
plants grow back.
Other locations are using the same
techniques to study the effects of
grazing and other land uses.

Change on the Range
Not only may global climate
change affect tomorrow's world-it
may already be shaping our natural
ARS scientists have discovered
that rangeland plants, like crop plants,
can grow more and use less water
when atmospheric C02 concentra-
tions rise.
"Shrubs have invaded and are in
some cases replacing native grass-
lands worldwide," says ARS plant
ecologist H. Wayne Polley of Tem-
ple, Texas. "Rising CO2 levels over
the past 200 years may be partially
responsible," he says.
That's because some plants seem
to benefit more than others from the
extra C02. The shrub mesquite,
Prosopis sp., is one of the winners.
"Woody plant populations tend to
increase as precipitation increases.
Improving plants' water use efficien-
cy could be having the same effect as
having more rain," Polley says.
In much of Texas, mesquite has
replaced the native prairie grasses.
Such a shift in the vegetation can
have widespread impacts: less forage
available for livestock grazing, a shift
in wildlife species that inhabit the
area, changes in soil nutrient cycling,
and increased erosion because shal-

Inside an open-top chamber, plant
physiologists Jack Morgan (left) and Dan
LeCain measure photosynthesis taking
place in prairie grasses grown under
elevated C02.

low-rooted grasses no longer hold
soil in place.
Polley and colleagues are now
looking at mesquite genetics, to see
if some of the plants are better able
than others to use the increased C02.
"If we find such genetic variabili-
ty, then natural selection may be
helping mesquite become more abun-
dant," he says.
The grass species may also be
Right now, warm-season grasses
like blue grama, Bouteloua gracilis,
dominate the shortgrass prairie in
Colorado. Warm-season grasses are
most productive during the summer
months, while cool-season grasses
like western wheatgrass, Pascopyrum
smithii, grow in spring and fall.
In growth chamber studies, ARS
plant physiologist Jack A. Morgan
found that photosynthesis in cool-
season grasses increases as atmo-
spheric C02 rises.

"From research on other plants, we
expected the cool-season grasses to
respond more than the warm-season
grasses," Morgan says. "Eventually
that could give cool-season plants a
competitive advantage and shift the
ecosystem's species composition."
But he also found that the warm-
season grasses respond more than
previously believed to additional
C02. Like mesquite, both types of
grasses use less water and grow more.
Two complications in the future
scenario are potential temperature
increases and reduced forage quality.
"If temperatures go up without a
corresponding increase in precipita-
tion," says Morgan, "the soil may dry
out enough each growing season that
the plants can't take full advantage of
the increased C02."
Morgan's and Polley's teams also
found that while the plants grow
larger, the concentration of nitrogen
in the plant tissues goes down. That's
important because protein, a key
nutritional component of forage
grasses, depends on the nitrogen.
"The end result is more forage, but of
reduced quality," says Morgan.

SALSA-the SemiArid Land
Surface Atmosphere Program
Arid regions, which get less than
10 inches of precipitation annually,
and semiarid regions, which get from
10 to 20 inches, constitute about one-
third of the Earth's land area. Any
changes the planet experiences in the
future could have a profound effect
on these regions because there is a
close relationship between these
ecosystems' health and the weather
and water cycle. To help measure and
predict such long-term changes,
scientists from nine federal agencies,
eight universities, six foreign agen-
cies, and one private organization are
working together on the SALSA

Agricultural Research/July 1997

Their outdoor laboratory is the
2,500-square-mile Upper San Pedro
River Basin that spans the border
between northern Sonora in Mexico
and southeastern Arizona. Scientists
hope SALSA will establish this basin
as the North American site where
remotely sensed data from satellites
and aircraft, coupled with computer
models that predict changes, will be
calibrated and validated.
"The basin is ideal for our re-
search; it contains climatic diversity
and five distinct vegetation types
over distances as short as 12 miles.
The Nature Conservancy has de-
clared the San Pedro riparian corridor
one of the 'Twelve Great Places of
the Western Hemisphere'," says
David C. Goodrich. An ARS hydrau-
lic engineer at Tucson, he heads the
overall SALSA program, with ARS
as the lead agency.
Intensive hydrologic data have
been collected over the past 30 years
from part of this basin, ARS' Walnut
Gulch Experimental Watershed. This
information will be added to that
collected as part of SALSA, which
began in 1995.
This year, the program will con-
centrate on understanding the San
Pedro riparian system on the U.S.
side of the border. Scientists will es-
tablish baseline data by measuring
surface water, groundwater, and tran-
spiration. They'll compare their mea-
surements to readings collected from
satellites and aircraft during five
overflights through October 1997.
Over the entire basin, SALSA
team members from ARS, the U.S.
Environmental Protection Agency,
Tennessee Valley Authority, Univer-
sity of Arizona, and Mexico and
France will concentrate on energy
balance measurements from several
areas, vegetative characterization
from satellites, and large-scale land
cover change using ground and
historical satellite data.

Kange scientist Jon Hanson notes the ettects of tour global change scenarios on calf
weaning weights and compares them with the Range Dependency Index (on the monitor)
showing the percentage of a region's income that is linked to range beef production.

Scientists expect to monitor how
humans change the area. "We can
already see some evidence from
satellite images. The U.S.-Mexico
border is clearly visible because of
different livestock grazing practices
in the two countries. The presence
and possible expansion of an enor-
mous copper mining operation at the
headwaters of the San Pedro may
also have significant impact on the
basin's water quality and quantity,"
adds Goodrich.
Future plans call for collecting and
archiving information like precipita-
tion and solar radiation from the
different areas over a 5- to 10-year
period. Then a basin-scale hydrologi-
cal model will integrate these and
other variables.
Scientists hope the effort will
improve how computer models
predict the impact of environmental
changes on the hydrology and
ecology of this and other large basins.

Farming in the Future
Inside growth chambers in L.
Hartwell Allen's Florida test field,
rice, soybeans, and forage plants
such as bahia grass are growing in air
with twice the C02 found in today's
atmosphere. Allen's an ARS soil
scientist in Gainesville.

CO2 gas-pumped into the sunlit
chambers, temporary plastic-covered
greenhouses, and other structures-
creates a mixture of air similar to
what scientists predict could be
present in the Earth's atmosphere
within the next century. The experi-
ments, begun as collaborative studies
with the U.S. Department of Energy,
are in their 15th year.
Allen and others have found that
elevated CO2 concentrations increase
plant photosynthesis. But vegetative
growth-roots, leaves, and stems-
increases more than seed production.
"That means that in the future,
scientists may have to breed plant
varieties that are capable of produc-
ing more seed in the higher CO2
atmosphere," Allen says.
Results by ARS researchers
nationwide give farmers a glimpse
into how their jobs might change as
CO2 concentrations-and possibly
Rice growers in temperate areas
are likely to see a yield increase as
the C02 concentration rises, Allen
and University of Florida colleagues
found. But if temperatures increase
too much, yields are expected to
decline. In experiments with both
current and doubled C02 concentra-
tions, today's rice cultivars produced

Agricultural Research/July 1997

the greatest yield at an average daily
temperature of about 80oF and the
least when daily average tempera-
tures rose to 97oF. Since most rice is
grown at temperatures close to the
optimum of 80"F, temperatures
would have to rise far more than
modeled predictions before yields
would be seriously reduced.
Soybeans seem to be able to
tolerate slightly higher temperatures
than rice, Allen says. With increased
CO2, farmers should see up to 30
percent higher soybean yields-even
if temperatures rise as much as 50F-
as long as rainfall remains adequate.
Southern beef producers may
have to provide more shade, more wa-
ter, and high-protein supplements to
keep cow-calf operations profitable.
That's both because the animals
would have to tolerate more heat and
because the forage quality may de-
cline in southern areas if temperatures
rise significantly, according to the
SPUR2 model developed by Jon Han-
son. Northern producers would fare
better, with increased forage quality.
Nitrate leaching into ground-
water could decrease as CO2 increas-
es, according to experiments in Au-
burn, Alabama, by ARS soil scientist
H. Allen Torbert and plant physiolo-
gists Hugo H. Rogers and Steven A.
Prior. They found that soybean and
grain sorghum plants grew larger and
tied up more soil nitrogen-includ-
ing nitrogen from fertilizer-under
elevated C02 concentrations.
Even after the plants died, less
nitrogen moved through the soil
towards groundwater. "Because the
plants are bigger, the residue con-
tains more carbon and a higher
carbon-to-nitrogen ratio," says
Torbert, who's based in Temple,
Texas. "The microbes that decom-
pose the plants tie up more of the
nitrogen in order to use the larger
amount of carbon." The bottom line:
most of the nitrogen stays in the soil.
Increased plant growth under
Agricultural Research/July 1997

elevated C02 and higher temperatures
could help reduce water runoff and
related soil erosion in the Midwest,
based on computer modeling done in
West Lafayette, Indiana, by ARS
hydrologist M. Reza Savabi. That's
because the additional growth pro-
vides a larger plant canopy, which
reduces the formation of a hard crust
on the soil surface. That allows more
rainfall to infiltrate the soil.
Environmental stresses that
normally decrease crop yields, such as
air pollution or moisture stress, could
be partially ameliorated with higher
C02 concentrations, according to

work led by ARS plant pathologist
Allen S. Heagle in Raleigh, North
Carolina. "That means increased C02
would have a greater benefit for crop
yields during dry seasons and where
concentrations of ozone are high,"
says Heagle.
Alaskan farmers could get
greater yields of barley and potatoes,
says ARS soil scientist Verlan L.
Cochran, who was at Fairbanks until
1995. Today, even under the 24-hour
daylight of Alaskan summers, plants
stop photosynthesis as the light
intensity weakens in the early morn-
ing hours. But in experiments with
elevated C02, photosynthesis didn't
stop. That meant higher yields and an
earlier harvest.
Increased C02 would lead to
higher wheat yields-about 10
percent more under well-watered
conditions and up to 20 percent more
than would be typical during drought,
according to research by Kimball in
Phoenix. If there's not too much
global warming, some farmers may
even save irrigation water because
wheat plants use less water in C02-
rich air. Kimball performed these and
other experiments as part of the
FACE project.
Despite the extensive research to
date, scientists are still working to
better predict the effects of global
environmental changes on agricul-
ture. The good news is that we have
time to mitigate change and adapt to
it, and ARS research will continue to
work towards both goals. "In the long
run," says Heagle, "we can minimize
the effects of global change on
agriculture by improving our crop
cultivars and modifying our cultural
practices."-By Kathryn Barry
Stelljes.. Sean Adams, Don Comis,
Dawn Lyons-Johnson, Dennis
Senft, and Marcia Wood contributed
to this article.

Need Information About Global
Change? Just ASK.

Searching for information on the
Internet can be frustrating. You
search for table china, but you get
hundreds of links about the People's
Republic of China. ARS' National
Agricultural Library is heading up a
pilot project to make it easier to
search for information on global
change. The Global Change-Assisted
Search for Knowledge (GC-ASK)
program provides bibliographic
information on global change-related
research papers from nine govern-
ment agencies.
"The goal is to develop a smarter
search engine that uses reliable
terminology to find just what you're
looking for," says Roberta Y. Rand.
She is the USDA global change data
and information coordinator. To visit
GC-ASK, go to http://
Roberta Y. Rand is at the UISDA-
ARS National Agricultural Library,
10301 Baltimore Ave., Beltsville, MD
20705-2350; phone (301) 504-6813,
fax (301) 504-6813, e-mail

The Ozone

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Basil Acock
Remote Sensing and Modeling Lab
Bldg. 007, 10300 Baltimore Ave.
Beltsville, MD 20705
Phone: (301) 504-5827
Fax: (301) 504-5823

L. Hartwell Allen
Crop Genetics and Environmental
Research Unit
University of Florida
Agronomy Physiology Lab, Bldg. 350
Gainesville, FL 32611-0965
Phone: (352) 392-6180
Fax: (352) 392-6139

Raymond F. Angell
Range/Meadow Forage Management
Research Unit
Star Rte. 1,4.51 Hwy. 205
Burns, OR 97720
Phone: (541) 573-2064
Fax: (541) 573-3042

Steven J. Britz/James A. Bunce
Climate Stress Laboratory
Bldg. 046A, 10300 Baltimore Ave.
Beltsville, MD 20705-2350
Phone: (301) 504-5609
Fax: (301) 504-6626

Verlan L. Cochran
Northern Plains Agricultural Research
1500 N. Central Ave.
Sidney, MT 59270
Phone: (406) 482-2020
Fax: (406) 482-5038
E-mail: vcochran @

Keith R. Cooley
Northwest Watershed Research Center
800 Park Blvd., Plaza IV, Suite 105
Boise, ID 83712-7716
Phone: (208) 422-0719
Fax: (208) 334-1502

Ronald F. Follett
Soil-Plant-Nutrient Research Unit
301 South Howes St., Room 407
Fort Collins, CO 80522-0470
Phone: (970) 490-8200
Fax: (970) 490-8213

Agricultural Research/July 1997

F r qtS ss I

David C. Goodrich
Southwest Watershed Research Center
2000 East Allen Rd.
Tucson, AZ 85719-1596
Phone: (520) 670-6380
Fax: (520) 670-5550
E-mail: goodrich @

Jon D. Hanson
Great Plains Systems Research Unit
301 South Howes St., Room 353
Fort Collins, CO 80522
Phone: (970) 490-8323
Fax: (970) 490-8310

Lowrey A. Harper
Southern Piedmont Conservation
Research Center
1420 Experiment Station Rd.
P.O. Box 555
Watkinsville, GA 30677
Phone: (706) 769-5631
Fax: (706) 769-8962

Allen S. Heagle
Air Quality, Plant Growth & Develop-
ment Research Unit
NCSU 1509 Varsity Dr.
Raleigh, NC 27606
Phone: (919) 515-3311
Fax: (919) 515-3593

Sherwood B. Idso
Bruce A. Kimball
U.S. Water Conservation Laboratory
4331 East Broadway Rd.
Phoenix, AZ 85040-8832
Phone: (602) 379-4356
Fax: (602) 379-4355

Herman S. Mayeux
USDA-ARS-National Program Staff
Bldg. 005, 10300 Baltimore Ave.
Beltsville, MD 20705-2350
Phone: (301) 504-5281
Fax: (301) 504-6231

Joseph E. Miller
Air Quality, Plant Growth & Develop-
ment Research Unit
NCSU 1509 Varsity Dr.
Raleigh, NC 27606
Phone: (919)515-3311
Fax: (919) 515-3593

Jack A. Morgan
Crops Research Laboratory
1701 Center Ave.
Fort Collins, CO 80526
Phone: (970) 498-4216
Fax: (970) 482-2909

H. Wayne Polley
Grassland, Soil & Water Research Lab
808 E. Blackland Rd.
Temple, TX 76502
Phone: (817) 770-6500
Fax: (817) 770-6561

Physicist Sherwood Idso (left) and soil
scientist Bruce Kimball assess fruit
production on an orange tree growing in
an open-top chamber with enriched C02.

Steven A. Prior
National Soil Dynamics Laboratory
P.O. Box 3439
Auburn, AL 36831-3439
Phone: (334) 887-8596
Fax: (334) 887-8597

Albert Rango
Hydrology Laboratory
Bldg. 007, 10300 Baltimore Ave.
Beltsville, MD 20705-2350
Phone: (301) 504-7490
Fax: (301) 504-8931

Donald C. Reicosky
North Central Soil Conservation
Research Laboratory
803 Iowa Ave.
Morris, MN 56267
Phone: (320) 589-3411
Fax: (320) 589-3787

Hugo H. Rogers
National Soil Dynamics Laboratory
P.O. Box 3439
Auburn, AL 36831-3439
Phone: (334) 887-8596
Fax: (334) 887-8597

M. Reza Savabi
Subtropical Horticulture Research
13601 Old Cutler Rd.
Miami, FL 33158-1334
Phone: (305) 238-9321
Fax: (305) 238-9330

Phillip L. Sims
Southern Plains Range Research Station
2000 18th St.
Woodward, OK 73801
S Phone: (405) 256-7449
Fax: (405) 256-1322

H. Allen Torbert
Grassland, Soil & Water Research Lab
808 E. Blackland Rd.
Temple, TX 76502
Phone: (817) 770-6500
Fax: (817) 770-6561

Agricultural Research/July 1997


Modeling Effects of Farm Decisions

new computer model may
soon help farmers and others
better understand how their
decisions on tillage method, timing
and type of irrigation, pesticide and
fertilizer applications, and selection of
crop rotations affect the environment.
"The Root Zone Water Quality
Model (RZWQM) was developed
over the past decade by a national
team of scientists," says Lajpat R.
Ahuja. A soil scientist with the
Agricultural Research Service, Ahuja
coordinates the root zone water
quality project and heads ARS' Great
Plains Systems Research Unit at Fort
Collins, Colorado.
"This simulation tool is needed to
study the effects of management
practices on soil water and movement
of chemicals that may be hazardous to
surface and groundwater quality,"
says Ahuja. "It's a model that inte-
grates management practices with
separate components dealing with
hydrology, plant growth, nutrients,
chemistry, and pesticides."
Actually, RZWQM is a series of
compatible modules that can be
attached or detached, as needed.
Computer programmers term this
flexibility "modular modeling." It
allows developers to test new sections
without having to rework any other
portions. They say RZWQM could
prove useful in many instances.
For example, major chemical
companies ignore so-called minor-use
pesticides because they do not want to
spend money proving to the U.S.
Environmental Protection Agency
(EPA) that new compounds are safe.
The cost of such testing would exceed
the profits likely to come from sale of
the products.
Chemical companies could use
RZWQM to get a quick answer on
which new compounds seem safe,
then conduct field studies on only
those most likely to gain EPA approv-
al. One chemical company, Zeneca

Ag Products of Wilmington, Dela-
ware, has shown interest in using the
model and assigned a scientist to
work with ARS on the model's
evaluation at Fort Collins.
"We hope that this model might be
used in the future to replace actual
experiments that involve root growth
or water movement," says ARS
rangeland scientist Jon D. Hanson.
"It could allow research agencies
to concentrate scarce money on a few
detailed projects aimed at gathering
baseline data. No longer would they
have to measure pesticide movements
everywhere," he says. "If the water
movement can be defined, the
computer can figure out the rest. This
reduces the need for expensive soil-
weighing equipment and drainage
solution samplers at many locations."
Farmers will also be aided by the
model's best management practices

SCOTT BAUER (K7688-11)

Computer specialist Ken Rojas (left) and
range scientist Jon Hanson use the Root
Zone Water Quality Model (RZWQM) to
examine nitrate distribution in a simulated
soil profile. The model enables scientists to
forecast potential environmental pollution,
such as from excessive nitrate leaching.

For example, if nitrogen move-
ment to groundwater supplies is a
potential problem in their area, they
can discover whether it's better to
plow in the fall or spring. RZWQM
might show that a farmer should not
apply all the nitrogen fertilizer at
planting time, but instead apply it in
two or three split applications.
Using nitrogen content-seen as
greenness of the crop-provided by
the model as a guide, farmers could
also apply nitrogen with irrigation
water when crops need the nutrient.
The model incorporates safe-
guards to ensure that the input data
entered by users is within a reason-
able range. If a range is exceeded, the
model explains what it's looking for,
or it instructs the user to refer to
tables in the user guide.
ARS computer specialist Ken W.
Rojas says, "The scope of science
RZWQM covers is just mind bog-
gling. Some scientists are using it to
understand how the whole plant-soil-
hydrologic system works."
"The model can run 20- to 30-
year-long simulations of one field,"
says ARS soil scientist Marvin J.
Shaffer. "These show how a mono-
culture or crop rotation would, under
various fertilization rates, contribute
to nitrate leaching and changes in soil
organic matter content, soil microbial
populations, and other indicators of
soil quality."

And the Refinements Continue
Last summer, ARS agricultural
engineer Hamid Farahani ran
RZWQM to simulate no-till dryland
corn production in eastern Colorado.
He and co-researchers learned that it
overpredicted yields on summit and
sideslopes, while underpredicting
them on lower areas. The researchers
found this was because the model
failed to accurately account for the
amount of water that ran off upper
areas onto lower portions of fields.

Agricultural Research/July 1997

Current versions can now interpret
this effect.
Gerald W. Buchleiter, an agricul-
tural engineer in the ARS Water
Management Research Unit at Fort
Collins, tested RZWQM using data
from a commercial farm in eastern
Colorado. He found that the model's
performance was acceptable as a
research tool for predicting corn
production on sandy soils under
center pivot irrigation. After more
testing, scientists will use RZWQM
to estimate the effects of various
farming practices on keeping fertiliz-
ers close to plant roots.
A larger test of the model was
conducted in the Corn Belt. It was
part of a regional study known as the
Management Systems Evaluation
Area project, a water-quality initia-
tive involving research at 10 sites in
Iowa, Minnesota, Missouri, Nebras-
ka, and Ohio.
In Missouri, ARS scientists evalu-
ated RZWQM to see how accurately
it could predict crop yields, surface
water runoff, and chemical movement
through the soil profile.
"In general, the model was accu-
rate in predicting corn and soybean
yields, surface runoff, and chemical
discharges in the runoff. But it
underestimated the movement of
chemicals downward through a soil
that had a subsurface layer of high
clay content," says soil scientist E.
Eugene Alberts, who leads the ARS
Cropping Systems and Water Quality
Research Unit at Columbia, Missouri.
The scientists are now modifying
the model to make it more accurate
for soils encountered in their tests. It
will then be able to predict formation
of the cracks and fractures in high
clay soils that permit more rapid
chemical movement. Other sites
where RZWQM is being run through
its paces include Tifton, Georgia;
Guelph, Ontario, Canada; Lisbon,
Portugal; and Bonn, Germany.

Data on rainfall intensities, solar radiation, minimum and maximum air temperatures,
and windspeed gathered from weather stations maintained by technician Dan Palic are
critical to the model's accuracy.

The next step is getting the
program to users. So far, the scien-
tists have trained more than 50
during 2- and 3-day sessions. And
ARS has entered into a cooperative
research and development agreement
for the commercialization of
RZWQM by Water Resources
Publications, LLC. This Englewood,
Colorado, company is now enhanc-
ing the manual so it is more user-
friendly and will make it, the pro-
gram documentation, and software
package available to customers.-By
Dennis Senft, ARS. Linda Cooke,
ARS, contributed to this article.
Lajpat R. Ahuja, Hamid Farahani,
Jon D. Hanson, Ken W. Rojas, and
Marvin J. Shaffer are in the USDA-
ARS Great Plains Systems Research
Unit, 301 S. Howes, P.O. Box E,
Fort Collins, CO 80522; phone
(970) 490-8315, fax (970) 490-8310,
Gerald W. Buchleiter is in the
USDA-ARS Water Management
Research Unit, Agricultural Engi-
neering Research Center, Colorado
State University, Fort Collins, CO
80523; phone (970) 491-8213, fax
(970) 491-8247, e-mail

Agricultural Research/July 1997

E. Eugene Alberts is in the USDA-
ARS Cropping Systems and Water
Quality Research Unit, Agricultural
Engineering Building, University of
Missouri, Columbia, MO 65211;
phone (573) 882-1144, fax (573) 882-
1115, e-mail eugene_alberts@ *

Soil core samples withdrawn from a field
near Fort Collins, Colorado, by technician
Mike Murphy (left) and soil scientist Laj
Ahuja will yield information on soil
horizons and their physical and chemical
properties for the RZWQM model.

Mending the Ties That Bind

Simple Repair Method for Broken Bands on Cotton Bales

hen L. Frank Baum's
Scarecrow lost some of his
straw along the yellow
brick road, it was easy enough for
Dorothy to restuff him and continue
on to Oz. Not so with cotton bales on
their way to market.
Cotton bales weighing about 500
pounds are held together by six or
eight restraining ties made of either
wire or steel straps. Occasionally, one
or more of the ties that encircle the
cotton bale breaks. About 2 percent of
the cotton bales produced in the
United States experience breakage of
one or more ties.
This means that each year, about
400,000 bales require repair, at a cost
of $4 to $14 million, estimates
agricultural engineer W. Stanley
Anthony, who is in the ARS Cotton
Ginning Research Unit at Stoneville,
The tie breakage can occur in the
gin within seconds after baling-or
days or weeks after packaging-or
before or during shipping to a ware-
house. Ties break or come off for a
variety of reasons. The cotton can be
too dry or not compressed tightly
enough. Other reasons for failure
include the ties' being too short,
defective, or damaged in handling.
For the cotton industry, tie break-
age means lost time and money. The
time and place at which the break
occurs determine how costly it can be
for the industry. If breakage happens
at the gin, the entire ginning operation
may have to stop. Many gins set their
defective bales aside and reband them
later, a procedure that requires four
people working for up to 30 minutes
to completely repackage the bale.
If breakage occurs after the bale
leaves the gin, damaged bales must be
reshipped to either a gin or another
location with a bale press available.
Repair costs range from $10 to $35
per bale, depending on the availability

of a press. Currently, the only equip-
ment that can be used for rebanding
costs over $300,000.
Textile mills can and do reject a
significant number of bales with
broken ties, according to Shay L.
Simpson, manager of marketing and
processing technology of the Nation-
al Cotton Council of America in
Memphis, Tennessee.
"If a mill rejects a bale for missing
ties, shippers must handle these bales
several more times to have the ties
replaced and the bales returned to the
mill. More handling puts stress on the
bale and creates the potential for
more tie breakage and bag failure that
could lead to possible contamina-
tion," says Simpson.
In the spring of 1996, Anthony
discussed the problem of broken ties
with Mississippi gin operator LeRoy



Deavenport. Drawing on past experi-
ence in cotton bale processing,
Anthony designed a machine for
rebanding broken ties. His device
permits one gin operator to fix broken
ties in about 10 minutes. Because of
the unique design of the device, an
operator can replace ties without
repackaging the entire cotton bale.
Anthony has tested several models
of the fix-it press, including manually
operated and automatic models, to
meet industry requirements. ARS and
Anthony are pursuing a patent on this
technology. The device may be
commercially available in the fall of
1997.-By Linda Cooke, ARS.
W. Stanley Anthony is at the
USDA-ARS Cotton Ginning Labora-
tory, P.O. Box 256, Stoneville, MS
38776; phone (601) 686-3094, fax
(601) 686-5483. *




I I-

The unique design of this device developed and demonstrated by ARS agricultural
engineer Stanley Anthony enables an operator to replace broken ties without repackaging
an entire cotton bale.

Agricultural Research/July 1997



String Trimmers for Curbing
Weeds in Row Crops

With the whir of a string-operated weed whacker,
corn and soybean farmers can take a big step to reduce
herbicide use that has the potential to contaminate
surface water near streams, wetlands, and wells.
"The only way to avoid surface water contamination
is to reduce herbicide use, and that's where the string
trimmer comes in," says Bill Donald. He is an agrono-
mist in the ARS Cropping Systems and Water Quality
Research Unit located at the University of Missouri in
Donald designed a system to cut weeds between crop
rows-using a lawn-type string trimmer-and reduce
herbicide application by as much as 60 percent.
ARS studies in 1993 and 1994 evaluated the surface
water quality at Goodwater Creek, an agricultural
watershed established as an experimental site by USDA
in 1971. The conclusion of those studies was that most
herbicides end up in surface water, rather than in
"If farmers banded herbicides in a small, narrow strip
over the crop row and mowed or whacked the weeds
between rows of corn and soybeans, they could get the
same yield as if there were no weeds," says Donald.
"Four years of field research in Missouri substantiate
this finding.
"The same system could apply to growing sorghum
and cotton, but at this time these crops haven't been
tested," he says.
Banding uses less herbicide per acre by treating only
the crop rows. And the weed stubble left between the
rows after using the weed whacker has an added benefit:
it helps prevent erosion by holding the soil in place.
Donald is currently developing a prototype string
trimmer that can be used on four rows at a time.-By
Linda Cooke, ARS.
William W. Donald is in the USDA-ARS Cropping
Systems and Water Quality Research Unit, University of
Missouri, Agricultural Engineering Bldg., Columbia, MO
65211; phone (573) 882-6404, fax (573) 882-1115, e-
mail william *

New Clues to Wheat Hardness

Scientists are a step closer to understanding the
chemistry behind the hardness of wheat kernels, thanks
to work at the Western Wheat Quality Laboratory in
Pullman, Washington.
"Hardness is perhaps the single most important trait
relating the grain to its end use," says ARS chemist
Craig Morris, who heads the laboratory. "Many proper-
ties of wheat flour that are important to manufacturers,
such as water absorption, depend on the initial hardness
or softness of the grain."
Bakers use hard wheat for bread and soft wheat for
cakes, cookies, and some noodles.
But the division between hard wheat and soft is not
always clear cut, Morris says. Pacific Northwest grow-
ers, for example, produce soft white wheat that's
popular in Asia. But some companies in the United
States have said the same soft wheat is too hard.
To resolve such discrepancies, Morris says that
researchers need to understand hardness on a fundamen-
tal level. Morris' latest discovery may help. He milled
wheat into flour and separated the starch from gluten
and other compounds.
Morris found that starch from soft wheat always
contains polar lipids-a specific type of fat-attached to
the surface of the starch molecules. Few or none of these
lipids attach to hard wheat starch.
"This gives us a biochemical marker to identify soft
and hard wheats. If the polar lipids are attached, the
starch is from soft wheat," he says.
Polar lipids are the second such discovery. A team of
researchers from the United Kingdom found in 1986
that a group of proteins called friabilins were also
perfectly associated with soft but not hard wheat.
Morris' research indicates that the two findings are
related. The friabilin proteins seem to bind to the lipids
rather than to the starch itself.
"When we determine what role these two compounds
play in creating soft wheat, we should be better able to
develop custom-tailored wheat," he says.-By Kathryn
Barry Stelljes, ARS.
Craig F. Morris is at the USDA-ARS Western Wheat
Quality Laboratory, Washington State University, John-
son Hall, Room 209, Pullman, WA 99164-6420; phone
(509) 335-4055, fax (509) 335-8573, e-mail *

Agricultural Research/July 1997

Dogwood, Hydrangea

Chemicals Foil Key Crop Pests

Hydrangeas and dogwoods have more than beautiful
flowers. The leaves from these plants contain chemicals
that kill or stunt the growth of two key crop pests, U.S.
Department of Agriculture scientists report.
Entomologists Billy R. Wiseman and James E. Carpen-
ter of USDA's Agricultural Research Service in Tifton,
Georgia, started on the research a few years ago as part of
an ongoing effort to find and test natural T AHLSTRAND
products from plants that can be used as
insecticides against the corn earworm and
fall armyworm.
To find the plants, Wiseman didn't
have to go far. He simply went into his
backyard and picked leaves not only from
his hydrangea bushes and dogwoods, but
also from black cherry and Bradford pear
At the agency's Insect Biology and
Population Management Research
Laboratory in Tifton, the researchers
dried the leaves, ground them up, and
added them to the pinto-bean-based lab The dark, wavy,
diet they feed to their earworm and is an infection t
ing toward a lea
armyworm larvae.
"The hydrangea diet killed 100 percent
of newly hatched larvae within 2 days," says Wiseman.
"The dogwood, cherry, and pear leaf diets severely
retarded the growth of the larvae. The larvae fed on them,
but they couldn't digest them."
Earworm larvae cause an estimated 5- to 10-percent
loss each year to corn, cotton, soybean, and other crops.
Armyworm larvae damage about $30 to $40 million
worth of corn, grasses, and other crops in the southeastern
United States.
The scientists are looking for an outside cooperator to
help identify the active insecticidal ingredients in the leaf
chemicals and to develop spray or bait formulations for
these natural pest controls. Once the active ingredients are
identified, Carpenter says, it may be possible to genetical-
ly engineer the insecticidal compounds into crop plants.-
By Sean Adams, ARS.
Billy R. Wiseman and James E. Carpenter are at the
USDA-ARS Insect Biology and Population Management
Research Laboratory, P.O. Box 748, Tifton, GA 31793;
phone (912) 387-2340/2348, fax (912) 387-2321, e-mail
bwiseman @ tifton. cpes.peachnet. edu *


Fuzzy Leaves Confuse Fungi

Like snakes on the head of the mythical Greek Medusa,
leafhairs on the surface of wheat and rye plants entangle
and confuse germinating fungal spores. This protects
these important grain crops from disease, say scientists at
the ARS Cereal Rust Laboratory in St. Paul, Minnesota.
Puccinia recondita, a fungal disease of wheat and rye,
infects thousands of acres of both crops each year and
causes millions of
dollars in crop
losses, says plant
pathologist David
Long. The fungus
is called a rust
because it discolors
leaves and makes
diseased plants
appear as though
they are oxidizing,
or rusting.
Based on pio-
neering work by
-tical line in the center of this micrograph ARS plant patholo-
of the fungus, Puccinia recondita, grow- gist John Roberts,
ening, or stoma. Magnified about 220x. wh is now retired,
who is now retired,
Long and others
were able to test a theory proposed by the late N.A. Cobb.
That USDA plant pathologist theorized that plant leaf
hairs interfere with fungal infection. The scientists
examined leaf surfaces with a scanning electron micro-
scope. They found that when fungal spores land on a leaf
surface, they send out tiny "infection tubes" that seek out
the plant's stomata-minuscule openings in the leaf
surface that allow the exchange of carbon dioxide.
"When a spore lands on a leaf surface with a lot of leaf
hairs, it becomes 'confused' and dies before the infection
tube can locate a stoma to complete the fungus' life
cycle," says Long.
He and Roberts showed a 27-percent reduction in
disease infestation in wheat and rye hybrids with higher
numbers of leaf hairs. "We think this is good information
for wheat and rye breeders to take under consideration
when developing new varieties," says Long. "In addition,
the leaf hairs also confer resistance to some insect
pests."-By Dawn Lyons-Johnson, ARS.
David L. Long is at the USDA-ARS Cereal Rust
Laboratory, University of Minnesota, 1551 Lindig, St.
Paul, MN 55108; telephone (612) 625-1284, fax (612)
649-5054, e-mail *

Agricultural Research/July 1997

Science Update

Technique Squeezes Potential
Anti-Cancer Compound From
A new technique makes possible,
for the first time, large-scale extrac-
tion of limonoid glucosides from
citrus. ARS scientists identified these
natural compounds nearly a decade
ago. Earlier food industry interest
centered on their role in reducing the
bitterness of juice. But renewed
interest is focused on their possible
anti-cancer potential. ARS and
Japanese researchers developed the
new extraction technique and have
applied for patent protection. In the
technique, citrus juice or citrus
molasses (a thick, dark-brown
byproduct of juice-making) passes
through a device lined with material
that collects up to 100 percent of the
limonoid glucosides. Washing out
the material with a solvent such as
alcohol yields a purified liquid. The
Japanese research group has test-
marketed a juice beverage with
added limonoid glucosides. Shin
Hasegawa, USDA-ARS Process
Chemistry and Engineering Unit,
Albany, California, phone (510) 559-
5819, e-mail

Wild Wheat Offers New Mildew
Wild wheat plants from Iran and
Armenia have genes that could let
U.S. growers cope better with
powdery mildew, a fungal disease.
Domestic wheat has some mildew-
fighting genes that have become less
effective over time. Now, for breed-
ers and other researchers, scientists
with ARS and North Carolina State
University have produced and
released three hybrid wheat strains
with stronger resistance. Powdery
mildew can strike in the Midwest but
is more common in the humid
Southeast. There, it claims 1 to 3
percent of the wheat crop every year,

translating to losses of $6.5 to $20
million. Chemical treatments can be
costly. The three new hybrids-
NC96BGTD-1. -2. and -3-showed
resistance to all strains of powdery
mildew in 3 years of field tests. To
create the hybrids, the scientists
pollinated domestic female wheat
plants with wild male plants. They
nourished the embryos in cell tissue
culture to produce mature plants.
These were fertilized with pollen
from another wild male plant, to
retain many of the other desirable
traits growers want. The wild wheat
came from germplasm collections at
ARS and Kansas State University.
Steven Leath, USDA-ARS Plant
Science Research Unit, Raleigh,
North Carolina, phone (919) 515-

Salmonella Gives Up a Few Secrets
What's a Salmonella to do? The
bacterium has to leap several hurdles
to move from the spleen of a hen-
house mouse into the eggs of a
chicken. Fortunately, the bacteria
rarely succeed. To do so, they must
withstand not only the immune
defenses of mice and chickens, but
also starvation, desiccation, oxygen,
heat, and other normal henhouse
hazards. Now, researchers are explor-
ing a molecular approach to deter-
mine why some Salmonella cells
change themselves to improve their
odds of infecting chickens and eggs.
The change occurs in the makeup of
carbohydrates and proteins on the
outside of the bacterial cell. Scientists
want to determine what environmen-
tal conditions trigger this change. The
answers could point to promising
countertactics. Already, the research
has yielded new practical advice:
Producers can use mice trapped
around the poultry house as sentinels
to monitor for the presence of the two
Salmonella phenotypes of greatest

concern. Both types inhabit mouse
spleens, so the rodents serve as a
reservoir for infection. Thanks to the
researchers, both phenot. pes can for
the first time be reliably distin-
guished. ARS' collaborators included
scientists at Stanford University,
University of Georgia. and Britain's
Cambridge University. Jean Guard-
Peiler. ARS-USDA Southeast Poultry
Research Laboratory, Athens, Geor-
gia, phone (706) 546-3446, e-mail

Second Areawide IPM Assault:
Corn Rootworms the Target
In June, airplanes began spraying
an ARS-developed corn-rootworm
bait on corn plants at four Corn Belt
sites and one in Texas. Air and
ground spraying marked the takeoff
of USDA's second areawide integrat-
ed pest management (IPM) project-
and the first to target corn pests. The
bait is powdered wild buffalo gourd
roots, which contain bitter cucurbita-
cin compounds that stimulate feeding
by rootworm beetles. The pests won't
enjoy their last meal for long, for
mixed with the bait is carbaryl
insecticide. But its per-acre active
ingredient is 95 to 98 percent less
than that in conventional spray. If the
bait works over large areas, expand-
ing its use to the entire Corn Belt
could cut corn insecticide use in half.
USDA's first areawide IPM project
began in 1995, aimed at codling
moths in Pacific Northwest apple and
pear orchards [See "With IPM,
Bigger Areas Are Better," Agricultur-
al Research, May 1997, pp. 4-8]. AR
magazine has scheduled a feature
story on the rootworm project for
October 1997. Larry Chandler,
USDA-ARS Northern Grain Insects
Research Laboratory, Brookings,
South Dakota, phone (605) 693-5239,

Agricultural Research/July 1997

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r- Almost all the nation's
grass seed comes from
Oregon, and producing
that seed isn't easy.

c It all started with the
Great Dig of 1995 on the
Spaulding Farm in
Missouri-the uncovering
of Eastern gamagrass'
secret to surviving both
droughts and severe

(e Scientists are breeding
even more nutritional
benefits into the newest
varieties of strawberries.

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