see POULTRYon page 7

Inside

Spring 2002

Agroforestry

Urban expansion into rural areas

where livestock are produced makes

maintaining good relationships a

challenge. Planting trees and shrubs as a

screen, however, can buffer odor, dust,

noise, and unpleasant views. Installing a vegetative filter or windbreak is an opportunity

for poultry producers to not only increase production efficiency, but to demonstrate their

commitment to being a good neighbor and an

environmental steward. 

Demonstrate Proactive Environmental

Stewardship

Dealing with ammonia emissions from

poultry houses and its contribution to atmosODOR IS MORE

THAN WHAT

MEETS YOUR NOSE

Inside 

3

4-5

CUTTING EDGES: 

TRAPPING AIRBORNE 

POLLUTANTS WITH FOREST EDGES

N a t i o n a l A g r o f o r e s t r y C e n t e r

You may have heard it referred to as the

“smell of money,” but some people just think

it stinks. It’s part of any livestock operation,

sewage treatment plant, industrial sites like

paper mills, or landfills... odor. The good

news is that agroforestry practices like windbreaks can help—-these Working Trees really earn their keep! Plant species, density, and

placement are elements to consider when

designing a buffer for odor. Keep in mind

that a well-designed vegetative screen

is also pleasing to the eye and can

provide livestock benefits, too.

CAN TREES MAKE 

A DIFFERENCE?

Windbreaks 

ease tension

between poultry farmers &

nearby community residents

6

SHELTERBELTS:

EMERGING TECHNOLOGIES

TO HELP CONTROL 

EMERGING ODORS

ODOR
brochures are designed to help you

inform and educate your clients

including community members,

landowners, youth, and others. They

are written for the landowner and

developed especially to aid you with

publicity and technology transfer to

get Working Trees applied on the

ground.

Visit our website for a preview

of any of NAC’s Working Trees

brochures or coordinating displays:

www.unl.edu/nac. You can also order

publications from the website or, if

you prefer, contact Nancy Hammond

at: nhammond@fs.fed.us or fax her

your request at 402-437-5712.

A New World Odor

NAC Director’s Corner

A commentary on the status of agroforestry

by Center Director, Dr. Greg Ruark

The U.S. continues to grow by more than 3,000,000 people

each year. This population pressure is causing most of our

cities to expand their boundaries. In addition, many families, in their search for open space, are constructing homes on

small tracts of rural land. As urban and residential dwellers venture into areas that were previously rural in character, the differences in lifestyles between farmers and city folks are becoming

painfully apparent. 

Farmers and ranchers view odors and dust that emanate from

livestock, chemical sprays, and fertilizers as integral to the practice

of agriculture and they have come to accept them as a part of life.

In recent years the movement towards increasingly larger operations for raising cattle, hogs, and poultry has resulted in situations

where large volumes of odor are generated at a given location. 

What to do? This is a question that many are now asking.

This issue of Inside Agroforestry attempts to identify and summarize what is known about the potential of agroforestry technologies, particularly windbreaks, to attenuate odors. Although there

have not been a lot of research studies done specifically on odor

modification with trees and shrubs, there are numerous studies that

were done for other purposes that suggest windbreaks can be

designed to help alleviate some of the problem. For example,

odor is attached to water and dust particles and is transported by

wind . Windbreaks have been designed to modify wind movement and trap dust for many decades. Tree species, especially

conifer types, have extensive leaf surface area that can interact

with water vapor and particulates that carry odor. Similarly,

denser plantings will have a greater ability to detain or deflect

odors and agroforestry plantings that are properly located with

respect to the sources of odor will be more effective. 

It must be cautioned that there is still much to learn. For

example, what are the relative benefits of placing windbreaks on

the upwind and downwind sides of odor sources? What tree and

shrub species are best and what planting densities and intervals

are needed? What are the maintenance requirements? Will it be

necessary to periodically rinse the windbreaks so their foliage can

retain its exchange capacity? However, one limitation we already

know is that, as with most things, if a livestock operation

or other odor generating activity gets very large not even

Working Trees can offer much help.

2 Inside Agroforestry | Spring 2002

The already-popular Working

Trees for Communities

(WTC) brochure will make its

second, new-and-improved debut

this summer. As agroforestry awareness continues to grow so do NAC’s

Working Tree publications. The

revised WTC brochure will address

many of the same issues as the first

brochure including: the rural/urban

interface, screening, dust and noise

control, and enhancing the environment for people, wildlife and recreation. But the new brochure will also

address storm water management,

wastewater management, and green

infrastructure.

All of the Working Trees

It’s back!!! And it’s better!!!
Spring 2002 | Inside Agroforestry 3

Joe Colletti and John Tyndall

Forestry Department, Iowa State University

In a March 24, 2002 editorial the Des

Moines Register asserts that “ . . . a clean

environment is essential to the progress and

prosperity in Iowa.” They also indicate that

Iowa could lead the nation in both hogs produced and clean air.

Because odor is very difficult to measure and human perception is variable, the

odor issue is complex and requires numerous approaches to provide desired outcomes.

The livestock industry uses a suite of technologies and management practices to deal

with air quality issues. About 95 percent of

livestock odor is controlled by standard

manure management. Yet livestock odor

control and clean air concerns continue to be

hotly debated. So, what new technologies

could be blended with standard livestock

practices to enhance odor control?

An emerging technology is shelterbelts.

Field-level shelterbelt and livestock odor

control research is limited, so initial estimates of shelterbelt efficacy are based on

allied research. Based on a large body of

knowledge, shelterbelts have the potential to

be an effective and inexpensive odor control

device particularly when combined with

other control methods. 

The potential of shelterbelts is related

to livestock odor characteristics, such as:

odor sources are at ground level, odor

travels as aerosols and dust, and the odor

plume at times hugs the land. Because of

these characteristics, shelterbelts of even

modest heights (i.e. 20 to 30 feet) seem

ideal for plume interception and disruption. Shelterbelts are also adaptable to

most production and odor situations. 

There are several ways that shelterbelts can

ameliorate livestock odors:

•By facilitating dilution of odor into the lower

atmosphere - Shelterbelts create surface turbulence that intercepts and disrupts odor plumes.

They lower wind speeds over manure storage

units allowing for slower release of odor. 

•By encouraging dust and other aerosol deposition by reducing wind speeds - Wind tunnel

modeling of a three-row shelterbelt quantified

reductions of 35 percent to 56 percent in the

downwind transport of dust. Pesticide drift

research suggests that reduced wind speeds

cause drift pesticide to drop (70 percent to 90

percent) from the air stream. Simulation of tall

barriers around manure lagoons show reductions of 26 percent to 92 percent.

•By physical interception of dust and other

aerosols - A forest cleans the air of micro-particles twenty-fold better than barren land. Leaves

with complex shapes and large circumference to

area ratios collect particles most efficiently. 

•By acting as a sink for the chemical constituents of odor - Volatile Organic Compounds

(VOC’s) have an affinity to the cuticle of plant

leaves. They are adsorbed and absorbed. Microorganisms on plant surfaces can metabolize and

breakdown VOC’s.

•By providing a visual & aesthetic screen - A

well-landscaped livestock operation is much

more accepting to the public than one that is

not. Out of sight may be out of mind.

see SHELTERBELTSon page 7

Windbreaks seem to offer biological, physical, and chemical

characteristics that can cleanse

the air of odor compounds.

Shelterbelts: an answer to

odor concerns?
The science of

odor control is

more complex

than just

closing 

your

nose.

4 Inside Agroforestry | Spring 2002

ODOR IS MORE

THAN WHAT

MEETS THE NOSE

Livestock odor is becoming an increasingly contentious issue, primarily for

two reasons: 

1) Livestock operations are continuing to 

grow in size, and 

2) More people are moving into rural 

areas, thus closing in on many livestock

operations. 

These two changes over the past couple

of decades have set-up a collision course

between farmers and non-farmers as well as

neighbor against neighbor. Concerns about

odors from large facilities goes beyond nonfarm residents who may move toward the

facilities, but also include many farm neighbors when a large confinement facility

moves in next door. People do not like

unpleasant smells especially from sources

that do not provide them direct benefit.

To illustrate this dramatic change in

livestock operations, the Environmental

Protection Agency reports that the total

number of animal units increased about 4.5

million (about a three percent increase) from

1987 to 1992. However, the number of livestock operations has decreased during the

same period. 

Confined animal feeding operations are

major contributors in meeting the production demands of consumers for meat, milk,

poultry, and eggs. For this economical flow

of food to continue, producers must have

access to the best cost-effective technology

to produce the commodities while protecting

natural resources including air quality.

Odor Sources & Transmission

With a larger number of livestock in

greater concentrations, larger quantities of

animal waste need to be processed. The

United States annually produces about 130

times more animal waste than human waste.

Livestock odors occur as gases that are

released from microbial decomposition of

manure and other organic matter. These

gases can include from 80 to 200 different

compounds that can cause odor. Some odors

can be detected at extremely low concentrations. Ammonia and hydrogen sulfide (rotten egg smell) are two particularly troublesome odors. With so many possible odorous

compounds, the interactions among the different combinations can cause either more

or less odor than a direct sum of the individual gases. Odors can also be absorbed and

transmitted by dust particles.

There are a variety of livestock odor

sources including livestock buildings,

manure storage facilities, and during land

application of the waste material. These

sources can cause odor continuously or only

during certain times or conditions. For

example, the odor from a livestock building

is generally constant, but odor from land

application of livestock waste will occur

periodically and vary due to the weather

conditions at the time. 

However, predicting odor impacts can

be a difficult process. Because the odorous

gases and dust are transported by the wind,

the impact area and magnitude can change

frequently depending on the wind direction

and speed. Some of the gases are heavy and

travel more closely to the surface while the

lighter ones will disperse higher into the

atmosphere. The roughness of the surrounding ground surfaces can vary through the

year and will impact how much of the odorous dust can be trapped. 
completely disappear. However, the science

and technology of managing odors is continuing to develop. For example, the University

of Minnesota has developed the Odor from

Feedlots Setback Estimation Tool to aid

Minnesota livestock producers in siting new

livestock facilities. This tool is the result of

four years of data collection and field testing

with a variety of livestock facilities in

Minnesota. 

Windbreaks fall into this developing

category. Preliminary information suggests

that windbreaks may be able to provide

some odor mitigation. For more information about windbreaks and odor, see

Shelterbelts Answer to Growing Odor

Concerns on page 3. 

Adapted from Understanding Livestock

Odors by Ronald Sheffield, Animal Waste

Specialist and Robert Bottcher, Professor

and Ventilation Extension Specialist,

Biological and Agricultural Engineering

Publication AG-589, North Carolina State

University and Offset: Odor From Feedlots

Setback Estimation Tool by Larry Jacobson,

David Schmidt and Susan Wood, Dept. of

Biosystems and Ag. Eng. University of

Minnesota Extension Service. Publication

FO-07680-GO, 2001.

www.extension.umn.edu/distribution/livestocksystems/DI7680.

Normal 

Breathing.

Sniffing.

Olfactory 

Epithelium.

Olfactory 

Epithelium.

The measurements of odor are further complicated by the variables that can occur at a

site during sampling such as different weather conditions. Because of these variables, the

odor intensity at the time of sampling can

easily be more or less than one hour earlier.

Managing Odor

Odor management is a result of the

overall management of the farm operation.

General maintenance of the buildings and

the nutrition of the feed ration are normal

farm management needs that can influence

odor emissions. Waste management plans

have become a standard part of livestock

operations in recent years. Livestock odor

management techniques fall into three areas:

• Preventing the generation of odor - including

feed additives, aeration, manure additives, etc.

• Capturing and destroying the odor - including

biofilters, waste storage covers, organic mats, 

etc.

• Dispersing or disguising the odors - including

vegetative or structural windbreaks, setback 

distances, site selection, etc. 

The cost of several of the above techniques currently presents significant economic barriers to implementing them. There

are also some unanswered questions about

the effectiveness of some of the techniques.

Additional research is needed to refine the

different approaches and find the most technically and economically effective methods.

What does the future hold

for the co-existence of livestock

feeding facilities and the surrounding communities? The generation of livestock odor is a fact

of life and will probably never

The flow of air through the nose

during normal breathing and

sniffing. Used by permission of

St. Croix Sensory, Inc. (1997).

Odor Effects

People respond to odor differently.

Although the human olfactory organ is quite

sensitive, the response to odor is related

more to past memories or cultural experiences. There is not very much information

about the impact of odors on human health.

Most of the existing information refers to

the adverse health effects individual gases,

e.g. ammonia, or dust, but no specific information about odors. One study did show

that odors from a swine facility had a negative effect on the moods of neighbors such

as anger and frustration. These psychological impacts can be as significant as a person’s physical health. Due to these concerns, effort is warranted to minimize odors

thus benefiting the community and the livestock producers alike.

Assessing Odor

Measuring odor is a complex process.

Although work is underway to develop an

effective measuring device, the most common assessment approach, to date, involves

the use of panels of people who sniff odors

captured by an instrument from a particular

site. The panel will define the smell based

on several different parameters including:

• Concentration or threshold - what is the mini

mum detectable concentration level

• Intensity - the strength of the odor above a 

certain threshold

• Persistence - the rate of change of the intensity

of the odor

• Character - what the odor smells like such as

earthy, fruity, rotten, chemical, etc.

• Hedonic tone - the degree of acceptability or

offensiveness of the odor

Spring 2002 | Inside Agroforestry 5
6 Inside Agroforestry | Spring 2002

Forest Edges

Trap Airborne

Pollutants 

from Adjoining

Fields

Forest edges are a lot like windbreaks in that they represent a

sudden and dramatic change in vegetation and surface

structure that effect wind speed and direction. Researchers

at the Institute of Ecosystem Studies investigated the effects of

forest edges, as a result of forest fragmentation, on wind-borne

nutrients and pollutants. 

This study examined the concentrations of sulfur, nitrogen,

calcium and water at the forest edge, in the adjacent field and in

the forest interior. All of the edge measurements were taken within 10 feet of forest edge and the interior measurements were

taken between 75-90 feet of the forest edge. During the study

period the concentration of water was not discernably different in

the study zones. However, there was a marked increase in total

sulfur, dissolved inorganic nitrogen and calcium at the forest

edge over the amounts found in either the adjacent field or forest

interior. These researchers “...demonstrate that forest edges

adjoining agricultural or urban landscapes are effective at scavenging and concentrating airborne nutrients and pollutants and

that the intensity of this effect is partly determined by the structure of the forest edge. These filtering and concentrating functions may have important ramifications for below canopy ecological processes.” This research also indicates that the active filtering processes occur close to the forest or windbreak edge and that

windbreaks may not need to be extremely wide, greater than 90

feet, to have an influence on trapping airborne pollutants.

“In fact , the forest edges have been shown to act as

“hotspots” of deposition, showing up to a four-fold increase in

the rate of atmospheric delivery compared with nearby areas

without edges. Much of this enhanced deposition is thought to

result from the dry deposition of particles and gases from the

deposition of horizontally driven fog or cloud droplets. In these

cases, it is the abrupt structure of the forest edge that creates a

trap for horizontally driven materials.”

This research and similar research efforts indicate that windbreaks may be an effective tool in managing odors in urban and

rural landscapes.

Adapted from “Forest Edges as Nutrient and Pollutant

Concentrators: Potential Synergisms between Fragmentation,

Forest Canopies, and the Atmosphere,” Weathers, Cadenasso,

Pickett: Conservation Biology, vol. 15, No. 6, December 2001,

pages 1506-1514.

Inside Agroforestry covers the latest agroforestry news

and information, and reaches an average of 9,500 natural

resource professionals across the country and internationally three times per year. We’ve covered topics like: 

Green Infrastructure & Communities, Specialty 

Forest Products, Wildlife, Carbon, Marketing 

Agroforestry, Small Farms, Water Quality, 

Wildlife, and of course, Riparian Forest Buffers, 

Windbreaks, Living Snowfences, Silvopasture, 

and Alley Cropping.

If you or someone you know would like to be added to our

database or have updates to your address, please

contact Nancy Hammond at nhammond@fs.fed.us

or fax information to her at 402-437-5712.

Should you be receiving and 

reading Inside Agroforestry?
pelling evidence exists that they will help

to further reduce odor. 

For more information, contact Joe Colletti,

Associate Professor of Forest Economics or

John Tyndall, Research Assistant, Forestry

Department, Iowa State University, (515)

294-4912 or visit our website at

http://www.forestry.iastate.edu/res/

odor_mitigation.html

Spring 2002| Inside Agroforestry 7

Shelterbelts

continued from page 3

Figure 1. A shelterbelt system

design for a hypothetical swine

production facility. The numbers

refer to the functional interaction and means by which the

shelterbelt will mitigate livestock

odor. The number 1 refers to

creation of air mixing turbulence, the number 2 refers to

dust deposition, the number 3

refers to particulate interception,

and the number 4 refers to sites

of air pollution sinks. Other

important design considerations

include: livestock type, odor

sources, air/wind patterns, the

species of trees/shrubs used,

and aesthetics/screening.

Field for land 

Storage lagoon application

Waste storage

Service 

roads

Hog confinement

N

1,2

1,2

1,2,3,4

3,4,1,2

1,3,2,4

A generalized windbreak is shown in

Figure 1. This design provides “buffering”

around the sources of odor and is adaptable

for most types of livestock systems. 

Based on some direct and mostly

indirect analysis, shelterbelts seem to offer

biological, physical, and chemical characteristics that can cleanse the air of odor

compounds. Also, they are flexible in

design. Further, they are relatively low

cost adding only pennies (<$0.20) per animal and seem to provide psychologicalaesthetic values as well. Researchers agree

that multiple control strategies increase

the effectiveness of odor reduction.

Clearly much work needs to be done to

quantify the efficacy of specific shelterbelts and livestock operations, but comVentilation

pheric nitrogen and fine particulates is representative of challenges

that all animal-related agriculture may face in the future. Trees strategically planted on poultry farms may help reduce ammonia emissions

by physically capturing both ammonia gas and the ammonia-laden

dust particles. 

The roots of trees are effective in absorbing nutrients. More than

80 percent of nitrogen and phosphorus can be kept from entering

adjacent water courses through root absorption or reduction in overland flow. Trees also have the ability to clean the air by capturing

carbon dioxide. 

Increasing Production Efficiency

Properly established windbreaks are an energy-efficient, natural system that can reduce heating costs as much as 10 to 40 percent

and reduce cooling costs by 20 percent for poultry houses. 

Windbreaks can also serve as a living snowfence. A tree windbreak can capture up to 12 times more snow per foot of height than

a picket fence, and it is 90 percent less expensive.

Another potential benefit may be improved biosecurity. By

restricting airborne particulates, trees may aid in blocking airborne

poultry diseases from entering, as well as exiting, your farm.

Although trees around the perimeter of poultry houses offer

many potential advantages, there are some negative aspects to consider. These include: some land will be taken out of production,

cost of the trees, labor for planting and maintenance, restricted view

of poultry houses, limited farm access to designated roadways, and

a potential habitat for wild birds. 

Of course, success depends on individual farm situations,

house orientation, type of ventilation system, available tree species

and width of the windbreak. Service roads, loadout areas and anticipated width of the tree spread at maturity are all factors when considering tree spacing. Allow for property lines, dwellings, traffic

visibility, surface and subsurface drainage rights-of-way, and overhead and below-ground utilities when placing trees.

Desirable features of trees for use with poultry farms include

maximum vegetative density with complex leaf shapes, waxy or

“hairy” leaves for efficient filtering ability, tap or deep roots, wind

tolerance, low maintenance and care, medium to fast growth and

tolerance to nutrients found around houses. Shrubs and trees that

attract wild birds due to seeds or nesting site and those with a wide

crown that obstruct traffic may be undesirable for some operations.

Extracted from “The Benefits of Planting Trees Around 

Poultry Farms.” By George Malone, Extension Poultry Specialist

and Dorothy Abbott-Donnelly, Extension Agent-Renewable

Resources. University of Delaware Extension Bulletin 159.

www.rec.udel.edu/Poultry/tree_buffer.pdf

Poultry

continued from page 1
National Agroforestry Center

East Campus-UNL

Lincoln, Nebraska 68583-0822

PRSRT STD

POSTAGE & FEES PAID

USDA — FS

PERMIT NO G-40

June 27, 2002

Pacific Northwest Special Forest 

Products Council Workshop. 

Springfield, OR. Contact: John Hegg, 

541-683-6644, jhegg@or.blm.gov

July 13-17, 2002

Soil and Water Conservation Society 

2002 Annual Conference.

Indianapolis, IN. Contact: Nikki 

McClain, 765-747-5531, www.hoosier

chapterswcs.org/activities/settingpace

July 20, 2002

Association for Temperate 

Agroforestry Annual Meeting.

Lanesboro, MN. Contact: Dean 

Current, 612-624-4299, 

curre002@tc.umn.edu.

August 23-24, 2002

Special Forest Products Production 

and Marketing Conference. 

Sinsinawa, WI. Contact Mike Bolin, 

217-333-2778, m-bolin@uiuc.edu.

Official Business

Penalty for Private Use, $300

October 5-9, 2002

Society of American Foresters 

National Convention.

Winston-Salem, NC. www.safnet.org/ 

calendar/presentations.

October 25-26, 2002

Special Forest Products Production 

and Marketing Conference. Cape 

Girardeau, MO. Contact: Julie 

Rhoads, 573-882-3234, 

RhoadsJ@missouri.edu.

Agroforestry | Spring 2002 Inside

Upcoming Events

Inside Agroforestry is published quarterly by the USDA

National Agroforestry Center. 

Phone: 402-437-5178; Fax: 402-437-5712.

Greg Ruark, Center Director ext. 27

Michele Schoeneberger, FS Research Lead ext. 21

Rich Straight, FS Lead Agroforester ext. 24

Bruce Wight, NRCS Lead Agroforester ext. 36

Kimberly Stuhr, TT Specialist/IA Editor ext. 13

Ryan Dee, TT Assistant ext. 14

Mike Majeski, FS Agroforester

St. Paul, MN phone: 651-649-5240

Jim Robinson, NRCS Agroforester 

Fort Worth, TX phone: 817-509-3215

Gary Kuhn, NRCS Agroforester 

Spokane, WA phone: 509-358-7946

www.unl.edu/nac

The USDA National Agroforestry Center (NAC) is a partnership of the Forest Service, Research &

Development (Rocky Mountain Research Station) and State & Private Forestry and the Natural Resources

Conservation Service. The Center’s purpose is to accelerate the development and application of agroforestry

technologies to attain more economically, environmentally, and socially sustainable land-use systems. To

accomplish its mission, the Center interacts with a national network of partners and cooperators to conduct

research, develop technologies and tools, establish demonstrations, and provide useful information to natural

resource professionals.

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Any person who believes he or she has been discriminated against in any USDA-related activity should immediately contact the Secretary of Agriculture, Washington, DC 20250.

Opinions expressed in Inside Agroforestry are those of the author and do not necessarily represent the policy of the USDA

Forest Service and the USDA Natural Resources Conservation Service.

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