Overstory #238 - Windbreaks for livestock production facility odor mitigation

Windbreaks (shelterbelts, vegetative environmental buffers) placed around livestock production facilities as Working Trees can help mitigate the movement of odors and dust generated by these operations. Four primary factors are thought to contribute to these odor issues:

• Urban expansion has placed many more people into closer contact with agricultural operations.
• Large scale livestock confinement production has led to increased concentrations of manure.
• Heavy concentrations of odor emissions travel across highly modified landscapes relatively devoid of natural barriers.
• Market economics and regulatory policies create limited producer incentives to control activities beyond minimum regulatory requirements.

Windbreaks alone will not prevent these odor problems but can provide farmers and ranchers with a “fresh” environmental tool to help reduce negative visual perceptions and the detection of smell by neighbors and surrounding communities.

The potential of windbreaks to mitigate livestock odor arises from the tree/shrub impacts on the fundamental characteristics and physical behavior of the livestock odor plume. These livestock odor plume characteristics are:

• Odor plumes are typically at ground level; often have limited upward movement; are variable; and may be very extensive covering large land areas;
• Odors generated in animal facilities are intense and detectable at appreciable distances; often concentrate and travel on particulates; but odor perception by individuals is highly variable.

Odor windbreak design

Windbreak design and planting plans will vary for each livestock facility and farm field site. When designing a windbreak for any facility, consider the following: landowner goals, design details including prevention of hazards, appropriate site preparation, planting details, and maintenance.

Landowner goals

Determine goals and objectives based on the landowner’s desired future conditions for the planning area as compared to the existing conditions. This includes the desired resource uses, resource problem reductions, and on-site and off-site ecological protections. As resources are inventoried, their interactions analyzed, and alternatives formulated, objectives may need to be reviewed and modified. Items to consider for odor mitigation include optimizing visual screening, enhancing dilution, and promoting particulate interception.

Design details

Always design air quality windbreaks to not only optimize tree/odor bio-dynamics but also to prevent potential on-site hazards. While all sites are different, key potential hazards are:

• Problematic snow deposition: Prevention requires an understanding of prevailing winter wind direction(s), an understanding of windbreak snow dynamics across a range of species and planting configurations (e.g., spacing, number of rows, etc.), minimum planting distances from roads and other areas frequented by vehicles, buildings, and other structures (e.g., manure storage, feed structures, etc.).
• Impeding site and building ventilation: Prevention requires an understanding of summer and winter wind direction(s), an understanding of necessary wind flow through a site (e.g., naturally ventilated buildings require non impeded wind flow in the summer), and understanding the different building ventilation requirements to prevent unwanted back pressure. Adjust windbreak porosities/densities to meet air movement needs for naturally ventilated livestock confinement systems. For mechanically ventilated buildings, allow adequate space from ventilation intakes and outlets or maintenance areas to keep airflow optimized.
• Impeding on-site traffic visibility: Prevention requires an understanding of key on-site truck and other vehicle “sight lines” needed to and from access roads.

Windbreaks should consist of at least one to three rows of conifer and deciduous species. Two to three rows of trees can provide an ideal 60 percent windbreak density (or 40 percent porosity) for odor control. Windbreaks may be wider with more tree rows to incorporate design needs or address additional objectives, such as improved wildlife habitat. Shrubs are generally planted in the outside or inside rows, followed by conifers with deciduous hardwoods towards the middle or along the downwind side where they can grow more efficiently. Tree varieties and placement for the windbreak should be managed to maximize odor interception and dilution of air, and reduce odor leaving the source. Where site and facility conditions merit and allow, place plantings (not necessarily windbreaks) around the entire perimeter of the odor source. Even a site with a windbreak on one side that is strategically placed and designed can make a difference.

Livestock buildings and manure storage areas are best located within the quiet zone, 50 to 100 feet downwind of the windbreak. Windbreaks should also be at least 50 to 100 feet from access roads and driveways to prevent snowdrifts from blocking farm vehicles during winter and create visual impairment zones. Always remember that hazard risk changes as trees grow. What is not a hazard initially can become one as trees grow larger. Use wide “between row spacing” to increase particle surface area contact, enlarge canopy areas, and to help accelerate plant growth.

Odor windbreak planting and maintenance

Appropriate site preparation

Most animal facilities, particularly on windbreak retrofit situations, are effectively construction sites with highly compacted soils, minimal top soil and poor drainage. Appropriate site preparation will reduce tree mortality, increase tree growth and ultimately save money and time. Depending on the site any or all of the following may be necessary:

• deep plowing or subsoiling
• summer fallow
• (chemical carry-over)
• cover crops
• drainage practices
• buffer strips
• vegetation control
• bedding

Planting details

Selection of trees and shrubs to plant should vary for each livestock facility. Species selection should be based on site characteristics, (e.g. soil type, drainage, common wind conditions—speed and direction, annual precipitation), species adaptation and land user objectives.

Select several species of trees and shrubs for use in windbreaks to prevent loss or destruction of the entire windbreak if outbreaks of insect pests or tree diseases occur. Having diversity also offers a better chance for tree survival and offers increased wildlife benefits. To maximize particulate trapping, select species with high leaf surface roughness (plants with leaf hairs, leaf veins, small leaf size), complex leaf shapes, large leaf circumference to area ratios and medium to rapid growth rates.

Maintenance

Once established, the windbreak should be maintained at a density of 50 to 65 percent for best results for wind management. Weed management is absolutely critical during the first five years of tree establishment (maintain until the trees are free to grow) for optimum growth and plant health. Monitor vegetation for insect, disease, dust accumulation, and death problems and treat accordingly (e.g. chemical spraying, pruning, replanting, foliage washing). Supplemental watering may also be necessary to allow for high survival and adequate growth.

REFERENCES

Lin, X.J., S. Barrington, J. Nicell, D. Choiniere, and A. Vezina. 2006. Influence of windbreaks on livestock odour dispersion plume in the field. Agricultural Ecosystems and Environment 116: 263–272

Tyndall, J.C., and J.P. Colletti. 2001. Air Quality and Shelterbelts: Odor Mitigation and Livestock Production—A Literature Review. USDA National Agroforestry Center. Project No: 4124-4521-48-3209.

Tyndall, J.C., and J.P. Colletti. 2007. Mitigating Swine Odor with Strategically Designed Shelterbelt Systems: A Review. Agroforestry Systems Volume 69, Number 1/January 2007.