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Published: 2008-03-04 00:00:00

Effluent seems to be proving its status as a form of liquid gold.

Maize plants grown using dairy effluent appear to be just as healthy as those grown with commercial fertiliser in a trial currently underway in the Waikato.

The three-year trial began last year on four farms in Matamata, Orini, Ohaupo and Ngahape. It is investigating whether fertiliser inputs can be reduced or cut to zero when growing maize on effluent blocks, and whether crops benefit from having some fertiliser applied at critical development stages.

With the first crops now being harvested, participating farmers Mike and Sue Visser are eagerly awaiting dry matter yields and post-harvest soil tests.

The Vissers are sharemilking in Ngahape, half way between Te Awamutu and Otorohanga, running a 1070-cow dairy farm on behalf of the Haerepo Trust.

“Because of the drought, there’s been no leaching this year, so if the crop hasn’t taken up the nitrogen it’ll still be sitting in the top soil,” Mr Visser said.

“If we find that maize is a good tool for capturing some of the nitrogen and potassium that’s outside the root system of the ryegrass/clover pastures, we’ll certainly be ensuring that maize is cropped rotationally in our effluent area in the future.”

Mr Visser said while it was difficult to make an objective judgment, a walk through the crop showed no distinction between trial plots and the crop as a whole “looked strong”.

An equivalent paddock in a non-effluent area with the same soil type and maize hybrid would have cost him about $650 per hectare in fertiliser, meaning his potential savings could be that high.

Matamata farmers Wynn and Tony Brown, who are also taking part in the trial, are also experiencing good results so far.

“It’s early in the trial and it’s always difficult to judge by the eye, but there’s certainly no visual difference between the effluent crops and the crops fed solely on commercial fertiliser,” Mr Brown said.

“If anything, with the dry weather, the crop on the irrigation ground possibly looks stronger than some of the other crops. Our irrigation is going straight from a holding tank so it’s a lot higher in nitrogen than somebody who’d been running it from a settling pond, and maize loves nitrogen.

“On normal ground synthetic fertilisers would cost between $500-$700, so that’s potentially my cost saving. And given what current fertiliser prices are doing, it’ll be $700 plus next year if prices stay the same or increase, so that makes it even more attractive.”

Spreading effluent on paddocks is an environmentally friendly way to use it. However, if too much is put on too small an area, soil fertility can build to harmful levels. Accumulated nitrogen can cause environmental problems and high potassium in the soil can lead to animal health issues.

The maize trials were set up by Environment Waikato and the Foundation for Arable Research (FAR) with a substantial grant from the government’s Sustainable Farming Fund. They are supported by DairyNZ and Genetic Technologies.

They follow a successful pilot trial initiated by Gabriele Kaufler, sustainable agriculture coordinator with Environment Waikato, in 2006. Four different farms paddocks were treated, half with commercial fertiliser and half with effluent, topped up by a small amount of fertiliser to ensure crop nutrient requirements were met. The effluent blocks grew just as much maize but used less commercial fertiliser, with one farmer saving $320 per hectare.

Ms Kaufler said many farmers didn’t realise effluent was liquid gold.

“Farmers can make significant savings by using effluent to feed maize crops, and maize can also be used as a tool to mine excess soil nutrients and improve environmental performance.”

The key was that maize was a deep rooting crop, so it had the ability to scavenge much deeper into the soil and soak up nutrients inaccessible to grass.

“With grass, 90 per cent of the root mass is in the top 10cm of the soil, so all the nutrients that have leached deeper in the soil are simply inaccessible. Maize, on the other hand, will grow roots down to 1.5m, so you can retrieve nutrients that have already disappeared from the top soil.”

Originally from Germany, Ms Kaufler has seen maize crops used strategically in Europe to manage effluent and believes New Zealand farmers could also use the concept successfully.

“But to sell the idea to our farmers, we need to give them hard scientific data and test the concept in local soils. Many have always put fertiliser on their maize crop. It’s a kind of insurance policy and they don’t want to change because they feel it’s too risky.”

Mr Visser, who is the regional chair of the AgITO Waikato committee, a Fonterra networker, a New Zealand Dairy Industry Awards committee member and 2005 Waikato sharemilker of the year, said he had one concern before the trial began.

“The most expensive thing you can do with a paddock is grow a poor crop. But when I saw the amount of analysis that was going on to make sure crop requirements were not compromised, I was confident we weren’t going to jeopardize the chances of growing nice crops,” he said.

Mrs Visser, who is involved full time with running the farm, said the trial had highlighted the importance of testing nutrient levels in both soil and dairy effluent.

“You could go for years doing the same old thing,” she said.

“If farmers think they’ve got a recipe for growing a good crop they’re not going to change anything because it works, even if they’re using three times as much fertiliser as they need to. That’s probably why we need to show the figures to change people’s mindsets.

“For us it’s great to be getting something positive out of using dairy shed effluent and being able to quantify our financial gains, but it’s also about becoming more environmentally focused.”

Mike Parker project manager with FAR said the SFF trials were about saving growers money as well as creating the environmental benefits of reducing nitrogen and potassium.

“It’s early days yet, but savings to farmers could be considerable, and long term there could be potential for dairy farmers to send their effluent off to be used on commercial maize crops, saving both the grower and the farmer,” he said.

“It’s one of those few situations where everybody wins.”