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Slowing down nitrogen application


Dairy Exporter April 2014 pg 46


Anne Hardie


It's still early days for a controlled release nitrogen fertiliser to prove its worth, but Smartfert is being described as another management tool for farmers trying to cut down their nitrogen loss and costs.

Smartfert director Bruce Smith said nitrogen utilisation efficiency (NUE) was usually quite low with traditional nitrogen fertiliser  - less than 40% - with much of it either  lost into the air through volatilization, leached or tied up in the soil system.


The theory behind the controlled release nitrogen, which has had research carried out by AgResearch and on-farm trials, is that the vegetable oil-based polymer coating will slowly release nitrogen over a three-month period. Farm trials show this technology having a higher NUE than uncoated nitrogen fertiliser producing more dry matter per kg of nitrogen applied, said Smith.

"Because of the low NUE with traditional nitrogen fertilisers, farmers have been applying high rates of nitrogen to get the maximum production with a lot of added cost."


From 50,000 tonne of nitrogen applied annually onto New Zealand pasture in 1990, farmers today apply 350,000 tonne, said Smith. This high-nitrogen regime has lead to a reliance on ryegrass that leaves no room for clover and comes at a high cost.


"I see the use of Smartfert as a management tool for controlling the supply of plant available nitrogen.. When applying nitrogen, there's a lot of parameters to consider to ensure its most efficient use .


"The weather makes a huge difference and you need about 10ml of rain following an application of  urea which is the largest  form of nitrogen sold in the country. “

With urea nitrogen, if it sits on the ground without rain, it risks being dissolved by the dew then  losing a percentage of nitrogen into the air, he said. While in high rainfall areas such as the West Coast, the plants often don’t have the chance to utilise the nitrogen before it is washed away.


Soil temperature plays a big role with nitrogen up take as the plants ability to grow and take up nitrogen diminishes with soil temperatures below 10 degrees Celsius, he said. Yet having some readily available nitrogen for the plant to take up during these cold periods enables the plant to be more tolerant to the cold especially frosts.

"Farmers also need to understand the recycling of nitrogen from stock. For example, the paddocks closer to the dairy shed are stocked more frequently, therefore are likely to have higher residual nitrogen"

As controlled release nitrogen, Smartfert can be applied in late autumn and spring as part of a farmer's maintenance fertiliser programme rather than having a separate nitrogen application, he said. Farmers can mix and match Smartfert with other NPKS fertilisers like ammonium sulphate as part of their nutrient management.


Smith said regulatory requirements would force farmers to change their nitrogen management, but to do that they needed to understand nitrogen.


"The Overseer programme calculates nutrient management on the farm based on rainfall, stock, soil  and climate. This also tells the farmer how much nitrogen is theoretically  being leached and many are having to reduce their nitrogen to meet their regional requirements.


"Traditionally there has been only the cost of inputs versus the return from outputs to consider, but now farmers have got to recognise the environment and people. So they have to start thinking about their nitrogen inputs more holistically. It's a balance of profitability, people and planet.

Soil scientist and Agknowledge managing director Dr Doug Edmeades has carried out research with Smartfert and said controlled release nitrogen could be the holy grail of nitrogen fertiliser as it theoretically should make it more effective.


"Now we need to quantify what that benefit is. Is it more efficient and producing more kilograms of dry matter per kilogram of nitrogen applied?"


While he said the concept of a controlled release nitrogen fertiliser was exciting, it was yet to be proven.

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