Edmeades' laboratory work showed the rate of release of nitrogen can be controlled by the number of coatings applied to the urea, meaning products could be developed that release nitrogen at rates more closely matched to crop demand.

 

One version of Smartfert is already commercially available through Fertco and Ballance Agrinutrients who sells it as StrategeN. It's designed to release nitrogen from the encapsulated urea over 90-100 days.

 

"It fits well in crops with a high demand for nitrogen such as maize, potatoes and fodder crops like brassicas where it's hard to make repeated applications," the man behind it's development for use in NZ broadacre agriculture, Bruce Smith of Eko360, said.

 

Smith said the organic polymer coating, which made from vegetable oil and applied to urea in Malaysia, prevents the rapid release of nitrogen that comes from uncoated urea in warm soils, so volatilisation and leaching risk is reduced.

 

It also means ryegrass or other plants grow steadily in response to the fertiliser with less risk of luxury uptake and a spike in nitrate intake by grazing stock. Such a spike in intake can elevate nitrate leaching from urine patches and risks nitrate poisoning of stock.

 

"Because you don't get that flush of growth, just steady increase over a 90-day period the plant roots develop better so the plants are a lot more tolerant if it gets dry. They're sturdy, not soft," Smith said.

 

In grass-clover pastures, clover growth is observed to be more vigorous because it's not swamped by a flush of grass growth and the clover's nitrogen-fixing root rhizobia are more active. More nitrogen fixed naturally means overall need for fertiliser nitrogen is reduced. More clover also means pasture quality is improved and livestock production benefits are likely to be greater than the increase in drymatter alone, Smith said.

 

Smith suggested Smartfert may have particular use on hill country where it could be blended with annual capital fertiliser applications, providing extra nitrogen in areas where repeat low-rate top-dressing of nitrogen isn't practical and enhanced clover growth is even more beneficial. 

 

"Lambs could be two months ahead in terms of the time they take to get to slaughter," he said.

 

Environmentally, that means less methane emitted by every lamb produced, and less nitrogen returned in urine patches of sheep, or more importantly, cattle.

 

"There's a relationship between nitrogen intake in herbage and nitrogen excreted in urine, so if you cut the nitrogen intake by 20%, the reduction in nitrogen excreted in urine is likely to be much greater."

 

Edmeades described the treated fertiliser as controlled release rather than slow release, the rate of release being affected by the number of coatings, soil moisture and temperature.

 

"It's a chemical process that alters the size of the nano-pores in the coating and temperature alters the rate that chemical process goes on."

 

Smith said Smartfert's coating wasn't rigid so structural integrity during spreading shouldn't be a problem. There's also no problem with the product's ballistics, he said.

 

While at present just one form of coated urea is available, should demand for specific shorter or long-term release products emerge, different depths of coating could be applied. And the coating technology isn't limited to use on urea - a nitrogen-phosphate-potassium compound has already been coated, and there's no reason why other common fertiliser shouldn't be encapsulated if the demand is there, Smith said.

 

The coated urea can also be mixed with other fertiliser to extend the nutrient supply window.

 

"When blended with ammonium sulphate the ammonium sulphate provides some upfront readily available nitrogen plus sulphur with the controlled release nitrogen from Smartfert kicking in later."

 

At present the coated urea is about twice the price of standard urea but a substantial increase in use could mean that the premium comes down.

 

Edmeades' paper follows previous comments on the product and associated research reported in Country-Wide's August 2015 Heartland Agronomy issue. Edmeades is the science advisor to Bruce Smith and has no pecuniary interest in the product or company (Eko360 Limited).