Friday, March 29, 2024

Saving a valuable resource

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Gone are the days when effluent systems were designed solely by multiplying the herd size by the water usage by the storage required by regulatory authorities, DairyNZ consultant Logan Bowler says.
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“It was always a flawed process and sometimes, by fluke, farmers got it right, but it’s the old way of doing things,” he told the South Island Dairy Event.

“Now most councils are using the Dairy Effluent Storage Calculator which first looks at the farm’s soil types to determine effluent application criteria, effluent inputs such as cows numbers, dairy water use and catchment areas as well as climate data to determine the system design and appropriate storage volumes.

“When we calculate the figures it may end up that we need a lake rather than a pond which is when we can have a relook at what we are doing and how we’re doing it.”

He said soil type was the major factor and farmers needed to be aware of what soils they had on their land. Using low-risk soils for effluent irrigation instead of high-risk considerably reduced the size of the required storage.

“You need to know the risk of run-off to a waterway. Find your low-risk soils and that is where you can plan to irrigate effluent.”

Effluent cannot be irrigated on high-risk soils during wet, cold weather when soil moisture deficits were small and evapotranspiration rates were low. However low-risk soils could be irrigated after rainfall as they had drained sufficiently to allow the nutrients to be stripped from effluent and held within the soil.

“With soil risk having such a large influence on storage volumes it is often more cost-effective to pump effluent greater distances to low-risk soils than to build infrastructure needed for large storage volumes.”

The second thing to look at was how much water was being used during milking.

“A normal herringbone uses 70 litres/cow/day – that’s 10% for washing the plant, 25% for cleaning the dairy and 65% for hosing the yard. By installing a green-water-recycling yard-washing system, daily water use can by slashed by about 65% or, for a farm milking 500 cows, that’s 23,000 litres of water per day that does not need to be pumped from the ground, stored and pumped through an effluent irrigation system.

“It makes good sense to be saving a valuable resource, saving time, effort, and money as well as reducing storage.”

In high rainfall areas, diverting stormwater away from effluent ponds again reduced the size of storage required.

“Regardless of annual rainfall, it is common sense to have a stormwater diversion in place during winter when the cows are nowhere near the yard.”

Efficiently extracting solids also impacted on pond size and set-up.

“If you have fall from your dairy the two-pond system or weeping walls work well otherwise there are screw presses, slope screens and rotating drums.”

There were many types of ponds and farmers needed to do their homework to find out what suited their situation best.

“Tanks may seem like a more expensive option but if very small storage volumes are required, and for flat farms with high water tables and no fill to build an above-ground pond, they may be more cost-effective. They also go up fast and are stock- and child-proof.

“Don’t think there is a right system when it comes to effluent. None fits every farm and that’s why farmers have got to work out what is best for their situation.”

Care should be taken when ponds became anaerobic and began to smell.

“Don’t irrigate paddocks near neighbours or your staff housing and don’t irrigate at night when everyone is home and especially not when the marquee has gone up for the neighbour’s daughter’s wedding.”

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