Skip

Using Windbreaks to Reduce Odors Associated with Livestock Production Faci

Using Windbreaks to Reduce Odors Associated with Livestock Production Facilities1

Windbreak/Shelterbelt-Odor Control Conservation Practice Information Sheet (IS-MO380)

See Printable Version PDF for images, diagrams and figures

The following document requires Acrobat Reader.

   IS-MO380: Using Windbreaks to Reduce Odors Associated with Livestock Production Facilities  (PDF, 1 MB)
 

Introduction

Preliminary research and observations made by farmers suggest that windbreaks placed around livestock production facilities may effectively reduce movement of odors emitted by manure to neighboring properties. Essentially, trees can be 'put to work' to reduce the movement of livestock production odors off-site.

Although the idea of placing vegetative windbreaks and shelterbelts around agricultural buildings and farm fields is not new, additional benefits from farm windbreaks continue to be learned and tested. Windbreaks alone will not prevent odor problems associated with intensive livestock production but may provide farmers with one more tool to help reduce negative visual perceptions and detection of smell by neighbors and surrounding communities.

An odor-emitting source can include a livestock production barn, manure storage or a farm field where manure is being spread. Windbreaks have the ability to reduce odor concentrations significantly at or very near the source, which greatly improves the effectiveness of separation distances.

There are six ways that windbreaks and shelterbelts can reduce the effects of livestock odor and improve visual perception of production buildings:

  • Dilution and dispersion of gas concentrations of odor by a mixing effect created by windbreaks.
  • Deposition of odorous dusts and other aerosols (like snow fencing) to the windward and leeward sides of windbreaks.
  • Collection and storage (sinks) within tree wood of the chemical constituents of odor pollution.
  • Physical interception of dust and aerosols odor particles on leaves, needles and branches.
  • Containment of odor by placing windbreaks fore and/or aft of the odor source.
  • Aesthetic appearance:
  • Trees create a visual barrier to livestock barns -

  • Trees can make cropped fields and pastures more pleasing to look at -

  • Trees represent an 'environmental statement' to neighbors that the producer is making every effort to resolve odor problems in as many ways as possible.

Dilution and dispersion

Without wind management, odors emitted from livestock facilities and manure storage areas tend to travel along the ground as a plume with air movement, especially during atmospheric inversions with little or no dilution of odor occurring.

Windbreaks create an obstacle for moving air masses. When designed properly, windbreaks force turbulent fresh air up and over the tree row and will also moderate and evenly distribute a more gentle airflow through the trees. Less air movement past barns will mean less pickup and movement of odor off site.

It is believed that windbreaks have the ability to lift some of the odor plume into the lower atmosphere where winds aloft mix and dilute the odor. The greatest dilution of odor occurs above and downwind from the quiet zone created by the action of wind passing over the windbreak. Beyond the quiet zone, more fresh air and less odorous air returns to the ground, thereby reducing movement of livestock odors off site.

Approximately 60 percent of the wind should be deflected up and over the windbreak and 40 percent should pass through the canopy of the trees. Two to three rows of trees can provide an ideal 60 percent density (or 40 percent porosity) through the tree canopy. Windbreaks are less effective for odor reduction when wind is minimal but the visual appearance remains in place.

Windbreaks create a 'quiet zone' of air that measures a distance of 8 to 10 times the height of the tree row downwind of the windbreak, and an additional moderation of wind speeds 10 to 25 times tree height, beyond the windbreak. Back-pressure created by the blocking effect of the tree row also creates a small quiet zone upwind of the tree line that is equal to 2 to 3 times the height of the trees.

Livestock barns and manure storage areas are best located in the quiet zone 50 to 100 feet downwind of windbreaks. In addition, windbreaks located downwind of the odor source are also important for filtering, absorption and trapping odors. Therefore, placing windbreaks around the entire perimeter of livestock production areas is ideal. Windbreaks should also be at least 75 to 100 feet from access roads and driveways to prevent snowdrifts from blocking farm vehicles during winter.

Deposition of odorous dusts

Windbreaks create a physical barrier to wind and air movement. The trees absorb wind energy and reduce its speed near the ground. As a result, fewer dust particles and less odorous gases will be picked up by the air coming from livestock facilities. Also in calmer air, dusts and gases already caught up in the air will be more likely to settle back to the ground on the downwind side of the windbreak. This deposition effect is commonly seen with snow fencing where snow settles downwind of the fencing or trees due to reduced wind speed.

To be most effective for deposition of odorous dust, windbreaks need to be located upwind and downwind of odorous livestock facilities. Upwind windbreaks reduce the quantity of dust and odor that is picked up by wind, and windbreaks located downwind of the facilities will further reduce wind speeds to allow settling of odorous dusts that have become airborne.

For cropland, the same may hold true for reduction of odor movement where manure is being spread onto farm fields. Windbreaks established around the full perimeter of farm fields should reduce movement of odor and can accommodate winds that are approaching the farm from any direction.

Wind tunnel studies of mass transport have shown that windbreaks can remove 35 to 55 percent of dusts being carried in moving air which would provide a substantial reduction of offensive odors carried off-farm. The amount of dust that is picked up or allowed to settle will depend on wind speed, direction of the wind, density of windbreak trees, height of windbreak trees and number of windbreaks.

Page 2