Waste not, want not

To reduce their impact on the environment, farmers are being asked to cut down nutrients and effluent escaping into waterways.

To reduce their impact on the environment, farmers are being asked to cut down nutrients and effluent escaping into waterways. Richard Rennie examines the state of research into the solutions farmers and environmentalists are looking for.

Given the length of time the nation seems to have been heatedly discussing farm-related pollution of waterways, you could be forgiven for thinking farmers just had to buy a system off the shelf.

It isn’t quite that easy. The challenge in reducing the sector’s nutrient runoff is that there’s no simple answer to the intricate science of nutrient flows. There is huge complexity in preventing, capturing and using effluent and nutrients, and monitoring the results. There are hundreds of different pieces of hardware and many techniques, and as many different pieces of advice as there are environmental consultants.

The complexity has not stopped farmers making changes to their practices. The farming sector now invests millions of dollars annually into nutrient and effluent management and capture. The total investment to date has been estimated at $3 billion.

Waterway fencing alone accounts for almost 10 per cent of that. This has been in response to pressure on farmers to fence riparian strips around waterways. This initiative has accounted for 22,000km of waterways being fenced, at a cost of about $220 million.

Dr John Quinn, a NIWA scientist based in Hamilton, says, however, that public expectation has got ahead of what is currently possible in terms of greater nutrient management, despite these steps.

“Scientific study can provide answers to the most challenging questions, but with nutrient runoff, people have been feeling particularly anxious because the science and farm practices to combat it haven’t been developed yet.”

Management of nutrient runoff in some form is now commonplace on most dairy farms, and is driven as much by economics as it is by compliance and sustainability desires.

Put simply, reducing nutrient input and re-using nutrient output lowers the costs of running a farm.

Soil scientist Dr Doug Edmeades says the rule of thumb for a dairy farm is that effluent reapplied as fertiliser on a farm is the equivalent value to $25 a cow, or about $11,000 a year for an average size farm.

Integrated monitoring systems have also been developed to optimise application of the valuable waste. They gather weather data to calculate the best times to apply effluent to pasture.

Integrated with nutrient budgeting software, they can then calculate how much additional fertiliser is required. The value of such systems, and the effluent they apply, has even been recognised by fertiliser companies keen to take a responsible approach to managing the losses.

In 2011, fertiliser company Ballance invested in Ag Hub, an online cloud-based farm monitoring company whose software includes effluent management and control.

But the myriad ways nutrients get onto farms, and then into waterways, are trickier than can be caught by the thick fingers of most systems currently on farms.

For over a decade it has been clear to New Zealanders that nutrient and effluent management on farms is also critical to improving the state of rural waterways. The issue of ‘clean streams’ has become a hot topic for the nation. Moreover, the responsibility has been laid primarily at the feet of dairy farmers.

In 2002, Fish and Game started its controversial ‘Dirty Dairying’ campaign to highlight the impact of dairy farming on waterways. In 2003, Fonterra struck its Clean Streams Accord with government agencies to undertake on-farm work that would reduce “the impacts of dairying on the quality of New Zealand streams, rivers, lakes, ground water and wetlands”, so that “water is suitable for fish, drinking by stock and swimming”.

Dairy NZ sustainability strategy leader Dr Rick Pridmore says dairy farmers contributed to some pollution, but are not alone.

“Water quality in New Zealand, where it has got worse, has got worse from a large variety of sources. Dairy is one of the causes, dairy is not in denial, but we are just part of the issue.”

Pridmore is right.

In May 2014, Christchurch City Council data revealed major contaminants present in the Avon River and tributary streams, including E. coli from human waste, zinc from car brakes, and hydrocarbons and copper contaminants.

The report prompted councillors to point out the undue attention on farmers and that it was a wake up call for urban residents.

But no matter what the contribution from all human uses of land, it’s farming that is still getting the attention.

The majority of the public still think the quality of waterways and lakes are adequate or better. But according to a Lincoln University report¹, the numbers thinking it is ‘bad’ or ‘very bad’ have doubled since 2010.

Solely responsible or not, dairying appears to be making the single largest effort to curb its impact.

Pridmore says dairy farmers contributed more than $5 million per year to help fund research by councils trying to implement the Government’s National Policy Statement for Freshwater Management. This included $1 million to help improve Waituna Lagoon in Southland and $1.2 million to assist Waikato Regional Council with its waterways.

“Everybody has a nutrient management plan; everybody has a better effluent system and those aren’t cheap – they can be $200,000,” he says.

But despite the major investment in infrastructure, no single system offers an ‘off the shelf’ solution to nutrient loss in dairy systems.

Nutrient tool box

Dr John Quinn says there is no silver bullet because the problem is ‘diffuse farm pollution’ – that is, the sources of pollution are varied, as are the routes they take into waterways.

While whole-of-farm systems are useful, even these are not sufficiently refined or sophisticated for all catchments.

He says pollution can only be solved by identifying the different pathways pollution is taking to get into waterways on each farm and in each catchment. He says the solution is looking more like “a quiver of armaments to win the battle”, than a single silver bullet.

Based in Hamilton, Dr Quinn heads a team of ecologists working on some additional tools farmers can add to their nutrient mitigation ‘tool box’ in order to contain nutrient losses.

The work starts with recognition that the biological nature of a farming system means nutrient losses are not as easily identified and isolated as they are in an urban environment.

The diffuse nature of nitrogen leaching and phosphate runoff means the industry is also aware riparian planting and waterway fencing will only do so much to curtail those losses. Dr Quinn’s team are tasked with research that takes the slippery task of farm nutrient control a step further.

There is a variety of methods of dealing with nutrient losses in different regions, and even on different farms within a region.

Soil drainage, rainfall and topography can all significantly influence how a farm’s nutrient profile responds to management variables like stocking rates, wintering policies and fertiliser application.

“The biggest contrast is between the west and east coasts of the South Island. On the west you are dealing with four metres of rainfall a year, when you only require about one metre to sustain dairying, and then across the Alps you have systems operating on barely half a metre of rain, plus irrigation.”

The work by Dr Quinn’s team reflects the diversity of the environments across which intensive farming now operates in New Zealand, and the varied attempts to capture the nutrient losses before they end up in waterway systems.

NIWA wetlands researcher and aquatic ecologist Dr Chris Tanner has over two decades worth of experience researching wetland systems and their use in managing farm nutrient losses. Dr Tanner cautions that the systems are by no means a magic wand to dealing with sediment and nutrient runoff.

“Sediment is relatively easily dealt with, but nitrogen and phosphate require more area to absorb. In farm systems, you are also working with variable flow rates between years, and within seasons.”

Having the benefit of some long-term studies on wetland systems in Northland, Waikato and Southland is helping reveal some options farms can adopt. Configurations could include wetland systems with a phosphate filter built on the outlet point.

Dr Tanner says it is easy to underestimate the area required for a functioning wetland system – about two to three per cent of the farm area is required, about four hectares for an average dairy farm.

He suspects within 10 years wetland systems may be de-rigueur on dairy farms, once all lower cost ‘best practice’ steps have reduced nutrient losses as much as possible.

His work is also studying the use of wood chip filters to capture nitrogen losses, and has recently gained funding for one, along with a phosphate filter at Waituna, Southland.

The wood chips in the filters provide energy for microbial activity that converts the nitrogen present into low impact nitrogen gas.

Collaborating with Dr Tanner is environmental chemistry colleague Dr Chris Hickey who is researching methods to better capture nutrients using minerals. His work is incorporating lessons learned from managing nutrient levels in lakes Rotorua and Rotoiti.

Dosing the lake systems with aluminised zeolite has proved successful in helping absorb phosphates. The challenge for Dr Hickey has been to develop a zeolite type filter that can be applied across many hectares of farm land, and be fitted to the back end of Dr Tanner’s wetland or wood chip system design.

“There are still challenges to that. We are examining different compounds to use, including bauxites, and trying to get a better rate of nutrient binding per kilogram of compound, which is not as high as we would like at present.

“You also need to have some sort of wetland system in front of such a filter to remove the sediment first.”

Growing algae and capturing gas may also prove valuable methods for lowering a farm’s environmental footprint, and delivering bottom line financial return.

Researchers have discovered the methane lost in dairy farm effluent ponds is more significant than first realised, contributing to global warming and the loss of a useful biogas.

Work by NIWA's Dr Rupert Craggs has aided development of a relatively low cost approach to methane containment. Simply covering the first effluent pond in a farm system means the gas can be piped off and used to generate electricity.

Dr Craggs and Stephan Heubeck have developed a simple, low cost, covered anaerobic pond that is installed before the effluent storage pond. This improves effluent quality by removing solids, making irrigation easier, and captures biogas methane for heat and power generation.

Dr Craggs's research has shown that covered anaerobic ponds work well in all New Zealand climate conditions from Northland to Southland, and are economical for farms with over 600 cows, or fewer if the waste from a farm feed or wintering pad can be treated.

Combining effluent energy recovery from covered anaerobic ponds with photovoltaic solar energy production could enable farms to be energy self-sufficient.

“The covered anaerobic pond can be used like a battery, storing the biogas energy when the sun is shining, then using it when it is not.”

NIWA has several sites (in Taranaki, South Auckland and Waikato) successfully operating with biogas capture, and several others are being commissioned on South Canterbury and Southland farms, one in combination with solar.

Dr Craggs’s group is also examining the potential to remove effluent nutrients by growing algae in effluent ponds prior to irrigation, to help farms reduce nutrient loads in areas where nutrient caps will be applied.

The algae and captured nutrients are harvested and can be digested to biogas methane as an energy source and then used as a fertiliser substitute or possibly a protein feed supplement.

Research work has also included a focus on the type of habitat that flora and fauna need to thrive in, even when nitrogen and phosphate levels have been lowered using the methods being studied.

“Many farm water systems, like drains and streams, have been simplified and lost a lot of the structures that would provide shelter and shade for the likes of freshwater crayfish and whitebait,” says Dr Quinn.

Work has included trialling wooden structures in stream beds that provide shelter, but also alter stream water velocity and direction, helping ‘cleanse’ water by pushing it into filtering gravel areas, similar to what happens in aquarium tanks.

¹ Hughey, K.F.D., Kerr, G.N. and Cullen, R. 2013. Public Perceptions of New Zealand’s Environment: 2013. EOS Ecology, Christchurch.

The tension

The pressure is on for science to develop solutions. This year the tension over pollution from farms directly curtailed farming expansion for the first time.

• In Hawke’s Bay a board of inquiry ruled that the planned Ruataniwha Dam on the Tukituki River could go ahead, but that the river can’t take any more nitrogen. So it ruled that nitrogen in the Tukituki can’t rise above the current average level – which is about 0.8mg/L. That potentially prevents intensification of farming in the area, which was part of the rationale for the dam.

• In North Canterbury, Ngāi Tahu was denied resource consent to farm 23,000 dairy cows on land next to the Hurunui River. Government-appointed Environment Canterbury commissioners had issued a water plan that allowed for a 25 per cent increase in nitrates in the Hurunui River to accommodate more farming. But Environment Canterbury said adverse effects of the plan to convert 7000ha of forestry land to dairy farms was unacceptable.

What makes a good dairy effluent system?

A system must reliably:

• store effluent until conditions are suitable to apply it to land, and

• apply effluent to land in a controlled way – at a depth and intensity which match the soil moisture and infiltration conditions and topography.

On-farm benefits of good effluent management include:

• fertiliser savings by using the nutrients in effluent, and reducing nutrient losses off the farm

• preventing animal-health issues such as milk fever which can be caused by a build-up of potassium levels in the soil

• improved soil condition from the addition of organic matter, including microbial and worm activity, as well as aeration, drainage and water holding capacity

• complying with council rules or resource consent – this may lead to less frequent compliance visits and reduced monitoring fees.

Some ways farmers can reduce nutrient output

1. Prevent cattle entering waterways by using bridges and culverts over regular crossing points, fencing waterways, and riparian planting

2. Install drains to catch effluent washed off stock feed pads and milking areas, and pipe it to storage/treatment before re-use (e.g., irrigation)

3. Irrigation systems arranged to apply water to pasture monitor soil conditions to ensure water is needed and will soak in, rather than run off or drain through the soil

4. Nutrient budgets and soil testing – keeping account of the amount of nitrogen and phosphorus applied to pasture via any source, to minimise wastage and optimise pasture growth.

Say when

How much nutrient and effluent is too much?

The Government’s approach for managing fresh water is called the National Policy Statement on Freshwater Management 2014. The National Objectives Framework, or NOF, sets national-level bottom lines for two compulsory values for freshwater; ecosystem health and human health for recreation. Regional Councils are required to manage for these values within designated areas in each region, with community consultation.

The NOF has attributes for which bottom lines (and grades above those) are set and applied to rivers and lakes. The minimum requirement for human health is that the quality should be suitable for wading or boating. For ecosystem health there are bottom lines for the acceptable amounts of river-bed algae (toxic and non-toxic types) and bloom-forming algae in lakes, all of which need to be managed by controlling nutrient levels.

Nitrate and ammonia levels should be low enough to avoid toxicity impacts on all but the most sensitive stream life. Communities can decide on higher nutrient limits to provide greater protection against both toxic and eutrophication effects. The Government says the NOF attributes are a start and that further bottom lines will be set when there is more scientific information.

Some ways to reduce runoff with better nutrient management


• Irrigate dairy shed effluent to pasture

• Reduce wastage from fertiliser by using soil test results 

• Avoid soil compaction caused by overstocking

• Plant open-drain filter strips of vegetation along drains and streams (grasses and riparian vegetation)

• Avoid direct laneway runoff to waterways by diverting to pasture

• Don’t fertilise near/over streams or drains


• Optimise farm nutrient inputs with nutrient budgeting

• Provide feed pad systems for wintering animals, with effluent treated via oxidation ponds and irrigated when conditions are safe

• Use natural and constructed wetlands

Dave Allen
Without fencing, cows and their effluent enter waterways. [Dave Allen]
Chris Tanner
Tile drains act as a rapid conduit for farm effluent. [Chris Tanner]
Chris Tanner
Constructed wetlands incertercept and treat tile drainage flows from grazed pasture to natural waterways. [Chris Tanner]
Dave Allen
Farmer Neville Bar (L) and NIWA resource engineer Stephan Heubeck uses a gas analyser to measure levels of methane, carbon dioxide, hydrogen sulphide and oxygen from the covered anaerobic digester pond. [Dave Allen]