Feedlot waste management series:
Dust control
Environmental Scientists and Engineers, Delivery
Introduction
To date, dust has not been a major problem at Australian feedlots. However, with a move towards lower stocking densities and the increased establishment of feedlots in drier areas, dust problems will increase.
Due to the limited experience with dust problems in Australia, much of the information given below is taken from United States (US) literature and is not based on local experience.
Occurrence of dust
Obviously, dust problems develop during prolonged dry periods. Less obvious is the time of day when dust is generated. Observations in the US and Australia suggest that the worst problems develop during the late afternoon and at dusk. When temperatures drop, cattle that have been resting during the heat of the day become active. Apart from feeding and drinking, younger cattle tend to become playful. This creates considerable dust that `hangs' in the cool still evening air.
Reasons for controlling dust
Dust from both the feedlot yards and associated roads annoy farm workers as well as people living in nearby houses. In addition, dust can act as a carrier of odours. Excessive dust is detrimental to animal health and performance. Dust may irritate eyes and increase the susceptibility to diseases such as pinkeye (blight) and respiratory disorders as well as creating general stress.
Dust control options
As it is not practical to remove dust from the air, management efforts should be directed towards preventing dust from being created. The different approaches are:
Feedlot yards
- removal of excess manure
- increase stocking density
- water application
- chemical application
Roads and service areas
water application
oiling
chemical application
Removal of manure
An important step in reducing manure dust is the removal of excess manure from yards. Although the feedlot pad may contain stored moisture, dry, pulverised manure hampers dust control. Hence, minimising manure accumulation increases dust control effectiveness. A maximum depth of 25 mm of loose manure above the interface layer is recommended.
Water balance of the pad
Dust problems are likely to develop when the water removed from the pad by evaporation exceeds the water added to the pad by rainfall and manure.
The loss by evaporation is determined by the weather conditions and the moisture content of the pad. Obviously, during hot, dry, windy weather, the potential evaporation rate is highest. When the pad is wet (that is, immediately after rain), the actual evaporation from the pad is close to the potential rate. However, as the pad dries, moisture loss is restricted. The actual rate drops well below the potential. Hence, during hot dry conditions, when evaporation from a wet surface may exceed 10mm/day, the actual loss from the yards may only be 1 mm to 2 mm/day.
Effect of stocking density
Stocking density has a significant effect on the manure accumulation rate and moisture content of the pad.
Figure 1. Moisture added by manure to the pad each year. (Moisture is expressed as the equivalent mm of rainfall on an annual basis. Manure is faeces plus urine.)
Figure 1 shows the amount of water placed on the pad by cattle of different weights at different stocking densities. The moisture is expressed as equivalent mm of `rainfall' per day. It can be seen from this data that the moisture contribution for large cattle at 10 square meters per beast exceeds the daily evaporation rate of a dry pad as discussed above. For lighter cattle at 15 square meters per beast or more, the pad would tend to get drier.
Hence, the potential exists to use stocking density as a dust management tool. The feedlot manager could change stocking density from lighter rates in winter to heavy rates in summer. However, due to the great variability of the Australian climate, this approach should be used with caution. If a prolonged wet period were to occur during summer, then the high stocking density would result in heavy manure loads and wet pads. This would reduce animal performance and increase odour problems.
Water application
The most common and effective method of dust control in the US is the application of water to the feedlot surface. In Californian research, properly sprinkled feedlots generated up to 18 times less dust than untreated lots. Dust levels rose more than 850 % whenever water treatment was discontinued for seven days.
Water treatment should begin before dust becomes a problem. The aim is to maintain the surface manure at 25 % to 35 % moisture content. Dry surfaces at only 7 % to 10 % moisture cause dust. Wet surfaces at greater than 40 % moisture cause odour. The aim is to stay between these limits. Under these conditions, aerobic decomposition of the pad will occur with minimal release of odour.
The application rate should be adjusted to suit weather conditions and some trial-and-error is probably needed to obtain the best results. The following points should be noted:
- Californian research showed that daily watering gave
significantly better results than alternate day watering.
- An initial application of about 5 mm over the whole pad should be
followed up by frequent smaller applications.
- Water treatment for dust control will increase relative humidity. In humid weather, this will affect animal performance, as it will impair the animal's ability to lose body heat by evaporation. Hence, water should be applied during the early evening hours when the heat load on the animals is reduced. This also coincides with the period of heaviest dust creation.
Water requirements
As an estimate of the water required to control dust effectively, the following calculations have been undertaken.
Consider a 5000 head feedlot stocked at 15 sq meters/beast. The total yard area would then be 75,000sq meters. An initial application of 5 mm over the whole yard area would require 375,000 litres of water. If subsequent application of 2 mm were repeated 30 times over a summer period, then a total of almost 5 ML (5 million litres) would be required.
If dust is becoming a problem and a feedlot manager wishes to control dust with applications of water, they should carefully calculate the volumes required and compare this with their water supply.
Methods of application
In the US, water is applied to feedlot yards using either permanent sprinkler systems or water trucks. Both systems have advantages and disadvantages.
Permanent sprinklers
Advantages:
- treat large areas simultaneously
- apply water exactly when required
- low labour requirement
- can be automated
Disadvantages:
- high capital cost
- frequent maintenance required
- inflexible (difficult to correct if designed or installed incorrectly)
- vacant yards receive watering
- high evaporation loss during application
- location of sprinklers may affect yard cleaning
- leaking fittings cause wet spots and odour problems.
Water trucks
Advantages:
- lower capital cost
- more versatile and flexible
Disadvantages:
- high labour and operating costs
- difficulty in satisfying demand during peak periods
- need to enter yards to apply water
- risk of breakdowns
- time delays in refilling tank.
For most Australian applications where dust problems are only likely to be spasmodic, it would appear that the strategic use of water trucks would be the best solution.
Timing of water application
Because most dust is created late in the afternoon, it is preferable to apply water in the middle of the afternoon rather than early in the morning. Water applied in the morning will probably have evaporated away by the time the cattle start to create the dust cloud.
Chemical controls for dust
American experience is that chemical agents with demonstrated potential for dust control in construction and aviation applications have little effectiveness in feedlots. The only potential use for chemicals in Australia would appear to be the use of waste petroleum oils as dust suppressants on feed alleys and around service areas.
To date there does not appear to have been any use of chemical control in Australia.
Conclusion
As stocking densities decrease and feedlots become established in drier regions, generation of dust will become an important issue that lot feeders must address. Most dust is created in the late afternoon when the cattle that rest during the day become active. Dust control measures should therefore be targeted towards controlling dust generation at this time. Dust can be controlled by regularly cleaning yards, by keeping the moisture content of the pad and surrounding areas higher (by manipulating the stocking density or by applying water) or by chemical control.
Further information
DPI&F's intensive livestock environmental management web pages: http://www.dpi.qld.gov.au/ilem
To access DPI&F information, services and products
DPI&F Business Information Centre between 8 am and 6 pm weekdays: Phone 13 25 23 (Queensland residents); non-Queensland residents phone +61 7 3404 6999; E-mail: callweb@dpi.qld.gov.au.
This DPI&F Note is also published on DPI's PrimeNotes CD-ROM.
Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries and Fisheries has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.
Environmental management home
Last updated September 2003
