By Rick Koelsch
Roughly half of all neighbor complaints of livestock odors originate from land application of manure. A weather forecast and a little knowledge of odor dilution can be a powerful tool for keeping your neighbors happy, or at least avoiding those irate phone calls. This article summarizes those weather conditions that should be considered when planning manure application.
Incorporation of manure into the soil is always the “best” practice for controlling odor. Soil is an excellent filter for removing odors released by manure. However, maintaining residue cover to protect soil quality, reduce erosion, and conserve water does not always allow for manure to be incorporated.
Figure 1. Watching a weather forecast before land applying manure can reduce your neighbors’ odor exposure.
When manure cannot be incorporated, the next 36-hour period after land-applying manure is the most critical. Why? Good drying conditions over the next two days can significantly reduce the release of odors. In addition, the next two evenings are the most likely time when neighbors will experience odors. Especially when applying manure without incorporating it, pay close attention to the forecast for the 36 hours after application.
Figure 2. Wind direction is an important predictor for identifying which neighbors are at risk.
Predicted Wind Direction
Wind direction is the single most critical information for selecting fields for land application of manure. Odor plumes travel in the same direction as wind and spread out laterally very little. By identifying the edges of the field perpendicular to the wind and the wind’s direction, one can quickly identify the neighbors at greatest risk and those unlikely to be impacted.
For the two land application site options illustrated in Figure 2 (Fields A and B), Field A presents a much smaller risk to nearby neighbors than does Field B. By choosing a land application site ½ mile to the north for this southwest wind, the risk has been dramatically reduced. By paying attention to the wind directional forecast for a 36-hour period after applying manure, applicators can gauge the risk of odor affecting neighbors.
Evening Hours and Manure Application
Can you recall a time when you observed a smoke cloud hanging near the ground? Often this is observed when air temperatures are cooling and winds are light, most commonly during evening and nighttime hours. Under these conditions the smoke is not being diluted and is being held near the ground. Although we cannot see odors, the same atmospheric conditions create the greatest risk for neighbors experiencing odors (Table 1).
Table 1. Atmospheric conditions and their risk of holding odors near the ground.1
SURFACE
WIND SPEED (MPH) | DAYTIME SOLAR RADIATION | NIGHTTIME CLOUD COVER |
|---|
| STRONG | MODERATE | SLIGHT | >50 | <50% |
|---|
| <4.5 | Very Low Risk | Very Low Risk | Very Low Risk | High Risk | High Risk |
|---|
| 5 TO 7 | Very Low Risk | Very Low Risk | Low Risk | High Risk | High Risk |
|---|
| 7 TO 11 | Very Low Risk | Low Risk | Low Risk | Low Risk | High Risk |
|---|
| > 11 | Low Risk | Low Risk | Low Risk | Low Risk | Low Risk |
|---|
| 1 Based upon Pasquill-Giffort air stability classes (Pasquill, 1961). |
Under daytime conditions odor plumes are generally rising and diluted with fresh air to the point they are unlikely to be noticed by your neighbors. Bright sunshine and warming air are best for dispersing odors. Higher wind speeds (especially at night) also encourage greater mixing of fresh and odorous air and reduce odor risk. Note that nighttime hours with low wind speeds are the conditions most likely to expose neighbors to odors from land application.
Figure 3: Weather forecast for Columbus. Low wind speeds at night will place downwind neighbors at high risk for experiencing odors from a manure application. (Source: Aviation Weather Report and Forecast. Air Sports Net.)
Figure 4: Weather forecast for Sidney. Higher wind speeds during the evening of July 21 will reduce the risk of a neighbor experiencing odor from a nearby field receiving manure. (Source: Aviation Weather Report and Forecast. Air Sports Net.)
Weather Forecasts and Odors
Weather forecasts that provide 1) wind direction and speed; 2) sky conditions, and 3) temperature can be extremely valuable in deciding when and where to apply manure. Many weather services provide this information in their forecasts. A
viation Weather Report and Forecast (Figures 3 and 4) shares the important forecast information in an easily reviewed visual format.
For the Columbus Nebraska forecast (Figure 3), note that nighttime conditions will be producing higher risks for neighbors for the immediate future. No extended periods of good drying conditions are available before the high risk night conditions occur. Thus, if waiting for more desirable weather conditions is not a choice, what is your next best option? Note the forecast nighttime wind direction and use this information to select a land application site with the fewest downwind residences (mainly to the south and east in the Figure 2 example).
The weather forecast for Sidney (Figure 4) suggests that neighbors to the north of a land application site on July 20 are at risk for odor. Spreading manure July 19-20 should be avoided if neighbors reside to the north. Conditions for applying manure are more favorable on July 21 for good drying conditions and nighttime conditions that will disperse odors quickly. July 21 might be a good day for manure application on fields with greater neighbor pressure.
Picking the right weather conditions for land applying manure may not improve your popularity in the community, but it can go a long way with improving your community’s acceptance of livestock systems.