From Agriculture Victoria
WITH farm and herd size increasing over recent years, so too has the requirement for larger effluent ponds.
This concentrates odour in larger areas than in the past.
Odour emissions are usually produced due to an incomplete anaerobic decomposition of organic matter in manure.
When manure moisture content exceeds about 30 per cent, anaerobic conditions begin to prevail and odour is generated.
In addition to moisture content, the warmer the temperature, greater is the bacterial action resulting in faster rates of decomposition and thereby increased production of odour.
Odour is carried by the prevailing wind and becomes increasingly dispersed over distance.
On a hot, windy day, this dispersion is more rapid than on a cold, calm cloudless day or night.
In narrow, deep valleys odour tends to be confined and last longer, a consideration for a new dairy siting.
Around the dairy area, sources of odour are effluent ponds, solids separation systems, manure stock piles, feed pads, loafing areas and laneways and areas where manure (or silage) has become intermingled in mud.
Silage and stacks of spoiled silage or grain, storage areas for wet by-products, spilt feed, manure outside the washed areas such as yard entry and exit, around the sump and solids trap also contribute to “that smell”.
The siting of new dairy developments can take into account distance to neighbours (and likely future town/city growth), directions of the prevailing winds and topography as being the most important factor to avoid potential issues.
However, existing farms are ‘locked in’ so good management and regular maintenance should be foremost in mind to minimise issues and to maintain good relationships with nearby residents.
• Carry out de-sludging, manure spreading and effluent application when odour impacts can be minimised such as when prevailing winds blow away from the neighbours’ properties.
• Spread sludge and effluent onto a paddock about to be cultivated or direct drilled with a spring-sown or summer crop.
• Consider using effluent carts, which can inject effluent into the soil and reduce odour, versus dropping on the soil surface.
• Provide advanced warning or negotiate with neighbours so as not to interfere with their weekend activities.
• Try to design or modify existing areas to avoid wet manure building up in the first place as it will produce odour while it decomposes.
• Place a board or three around the top of the sump wall or nib wall on the entry laneway to the yard to minimise mess being dropped outside these areas.
• Design or modify laneways leading to the dairy to allow regular washing or scraping.
• Integrate the laneway and concreted feed pads into the effluent collection system, although that may not always be possible due to topographical barriers
If possible, ensure water can drain away from stockpiled solids and manure to the effluent system, as ponded water becomes anaerobic with potential for odour production.
Waste feed and manure from feedpads/laneways should be stored in triangular shaped windrows to shed rainfall and reduce the likelihood of creating anaerobic conditions within the pile.
New ponds, especially if constructed leading into the cooler months, will take some time for the decomposing bacteria to build up in numbers often producing odour until they do.
‘Seeding’ effluent from another active pond will enhance the activity of the ponds.
Sludge is comprised of either completely or partially digested organic matter, which settles out in the anaerobic pond.
The process of de-sludging will stir up the bottom solids and can be highly odorous so work with the wind in your favour.
Avoid shock loading a pond as this can upset or kill off the manure-decomposing bacteria and organic breakdown will reduce or stop.
This occurs when either a large-volume or a high-strength effluent is discharged into the pond on a single occasion such as spoiled milk or a large amount of feed pad scrapings was dumped into the pond.
Trees should not be established near ponds as roots may damage pond embankments or liners.
However, trees in a shelter belt can absorb some of the odourous compounds. Shelterbelts also create turbulence that disperses the odour upwards, particularly under stable night time conditions.
A proactive approach to managing odour can have many benefits and is achievable.