Jackie Harrigan

While farmers are coming around to spending money to upgrade their effluent infrastructure, Logan Bowler thinks a lot more needs to be done in effluent management.

“Putting in a pond is the start of the journey,” he says. The ex-Dairy NZ effluent specialist farms 400 cows in the Rangitikei and has recently set up his own Agblution Solutions consultancy.

(He really wanted to call the business “Crap Advice” but thought that could lack credibility if he was potentially called on as an expert witness in the Environment Court…)

Having worked for 10 years in effluent management, first at Horizons regional council and then Dairy NZ, Logan has been involved in setting up and then upgrading the Dairy Effluent Storage Calculator, helping farmers understand how much effluent capacity they will need to build.

“The industry has been flat out encouraging farmers to put in infrastructure but there is still a lot of work to do on management – is this an irrigation day or isn’t it? What is my soil water deficit? Do I understand those principles?”

“A very small percentage of farmers are set up to gather that data to make those decisions electronically.”

Thinking of your effluent as a nutrient resource is a good start, Bowler says.

“Use it as a resource rather than a waste product – just store it while the conditions for application are not right.

“Farmers have a nutrient and a water source – they need to get their heads around using it strategically – we personally have had great success putting it on to our new turnip crop in early December here in a dry summer – the effluent forced the germination of seed and we were feeding cows on it by mid-January.

“New grass in autumn is another place that effluent use is underrated – effluent can give new grass a really great early start.”

Evapotranspiration rates are relatively consistent each month year on year, dependent on rainfall – so people can do a soil water balance relatively easily, Bowler says.

Often you don’t need to measure it daily – you just need to know if it rained or not, and whether it was particularly sunny.

“Matching soil water deficits and application depths across the season, you need to have a fundamental knowledge about that.”

Less shed water usage = less volume

The biggest win farmers can have in terms of pond volume is reducing water usage in the shed.

“Everyone thinks rainfall is the biggest contributor – but that’s because when their pond is full and then it rains, the water falling into the pond and from the shed roof and yard is then overloading the pond.

“Farmers focus on rainfall but in all reality if they spend 10 minutes per day less on the hose, they can make a big difference.”

If farmers are using 70 litres/cow/day of washdown water for 280 days, that is about 20,000 litres/cow each year.”

Logan says by being aware of it, he and partner Kathy have managed to use half the industry standard 70l/cow/ day, measuring water use at 36-37l/cow.

“Washing only part of the yard at night, using the scraper to get rid of the big lumps, using a hydrofan nozzle – it’s a little bit more work and walking as it is used with a sweeping motion more like a broom but has the potential to save 30% of hosing water.

“You need a clean, hygienic shed – no one would argue with that – and we need to be stone-free. When cows are jammed into a yard too tight they can’t see where they are putting their feet and they stand on stones and get sore feet and lameness.

“But you could potentially hose the yard just once each day if you are not dragging lots of stones in.”

Wetting the yard before milking can help make it easier to clean down, but Logan says it’s not a common practice.


But allowing a rainfall event to soften the shit up is a good idea – wait until the outer parts of the yard are wet and softened before hosing, it will use a lot less water.

Logan says it is good to be aware and calculate the water use on your farm – use hosing time to work out how many litres are being used.

“Get out there and put the hose in a 200-litre drum – time it to fill, so you know how many litres/second the hose is running at. Then think about how long it takes to hose out the shed, and then how long to hose the yard.”

“Do the maths – minutes of hose time x 60 x however many litres/second, bingo… add in the plant wash water and you have an idea of how much water is being used each day. Divide by how many cows are milked and you can compare with the industry standard of 70l/cow/day of washdown water.

“Hooking up a water meter to measure is the best way or measuring water use in a sump or taking water measurements before and after from the washdown tank – but be aware that all the used cooler water goes through that tank.”

Shed water use is the biggest issue says Logan – it has the most impact on pond storage and is the most easily reduced.

It’s not just pond storage to be saved either, Logan says.

“Farmers are often paying to pump that water three or four times so the water is not free – it’s expensive when the pump has pulled it up from the bore into the shed, then into a tank, through the hose into the sump and then pumped out to the pond.”

Time spent shifting the effluent irrigator is also expensive, he says.

“Every litre not used in the shed is a litre that you are not chasing an irrigator within the paddock.”

Greenwash is another way of saving lots of clean water and pond space.

For the owner operator returns are really good showing a 20% payback to redo your yard and put green water wash in which is predominantly labour saving over a year of not shifting the irrigator or hosing the yard.

“Using green water you can halve your water use and halve the irrigator runs for the sake of putting a pump into the sump and putting it down the yard.

Concentrating the effluent through greenwash recirculation means the effluent is more nutrient-dense and “you get more bang for your buck irrigating it”.

Nutrient levels of effluent are hugely variable from farm to farm and across the season, so farmers use Overseer to calculate how big the effluent irrigation area should be.

“I don’t know how well the effluent areas are being managed, I think effluent areas are probably still getting more nutrient than the non-effluent area.

“One good way of lowering your footprint is by at least minimising fert spread in the effluent area. Size your effluent block on potassium requirements and then supplement the other nutrients via fertiliser.

“We just have to keep growing our understanding and getting better and better at managing this.

“Putting a pond in isn’t fixing all of the issues – it’s just the start of the process.”

Dairy effluent storage calculator

The new pond storage calculator is near to being released after work to put in new options particularly around storm water diversion and use of feedpads, Logan Bowler says.

The new version is more flexible with increased accuracy and new detail around multiple application depths and recognizing low or high-risk soils.

“Your storage need is reduced if you can apply shallow depths on to low-risk soils.”

When released, the calculator can be accessed from the DairyNZ website. dairynz.co.nz/environment/effluent/ effluent-storage/dairy-effluent-storage-calculator-desc/