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Large scale effluent pond part of wider farm strategy

Large scale effluent pond part of wider farm strategy
Greg and Gail Mitchell at their Patoka, Hawke’s Bay farm.

Greg and Gail Mitchell’s new 21,000 cubic metre effluent pond is expected to cater for their Patoka, Hawkes Bay farm’s needs for many years to come.Greg says the pond, three times the capacity the farm presently needs, is part of a wider strategy.

“We wanted to be able to store more water for the summer months and use it like an irrigation pond.” The large capacity enables the liquid to be applied to pastures at the right time, rather than being forced to irrigate when full, especially in an area that typically receives around 1800mm of rainfall annually.

“To build a pond twice as big, the bill isn’t twice as big. You can use that water in the summer months to keep growing grass.”In addition to the effluent storage, two 50m wide concrete bunker weeping walls are being installed, as well as a new feed pad.

According to Dairy NZ weeping walls are the most common method of passive solid separation.Raw effluent in a bunker is held in beds and effluent is separated by walls which are generally constructed of wooden slats or plastic panels.

Liquid seeps through the gaps in the walls, leaving the solid effluent behind in the sludge bed. “We went for the weeping wall system to take a lot of the solids out of the pond.”

A feature of the half-million dollar pond, designed by Taupo company Total Effluent and Dairy, is an outlet on the bottom so it can be drained from there.Because of this the pond does not need a stirrer, so no electrical connection is required.

It is also safer for staff as they do not need to walk on pontoons over the pond.“There’s a sump on the side that it drains to; the person that designed it all has done a pretty clever job. No one else had a pond design that could be emptied.”

The ability to separate the solids and liquids has advantages in applying effluent to pastures. In the case of the liquid, because the solids have been removed there is less nutrient loading.

Effluent can also be spread over a larger area because the solids can be spread on pastures with a muck spreader where irrigators cannot reach.It is planned to install a pond of the same design on Mitchell Dairy Farms second property, Kaweka Farm.

Farm working expenses across both farms is $4.27kgMS which is slightly higher than Greg would prefer, but this figure reflects the level of development in the businesses.It is Greg and Gail’s sixth season of ownership of the 460ha High Road and the fourth season owing Kaweka.

High Road peak milks 1550 cows.Last season, which Greg describes as very good, production was 608,000kgMS and this season the budget is based on 620,000kgMS, while Kaweka produced 327,000kgMS from 850 cows.

Apart from improving infrastructure, the main focus has been on improving the herds, eliminating lower performers through the selection of premier sires and by intensively regrassing to maximise production.

This strategy has been enormously successful; the High Road herd has been reduced by close to 1000 cows with no loss in production against the previous high input system.

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