Engineering every granule

Controlled-release fertilisers are not a new concept, but designing one that consistently delivers nitrogen when crops need it, while remaining commercially practical for large-scale agriculture, has proved far more challenging than simply coating a fertiliser granule. Tnue's Controlled Release Technology represents a different approach to that challenge. Rather than changing the chemistry of urea itself, the New Zealand-developed technology focuses on engineering how and when nitrogen leaves each individual granule.

At first glance, a granule of Tnue fertiliser looks little different from conventional urea. The difference lies in the polymer membrane surrounding each granule. This coating has been engineered to act as a controlled barrier rather than simply a protective shell. Once applied, soil moisture gradually penetrates the membrane, dissolving the urea contained inside. As the concentration of dissolved nitrogen increases, osmotic pressure develops within the granule, driving dissolved nitrogen through the polymer at a controlled rate. The result is a predictable diffusion process that responds to soil moisture and temperature rather than releasing the entire nitrogen load immediately after application.

This engineering approach is fundamentally different from enhanced efficiency fertilisers that rely on chemical inhibitors. Urease inhibitors work by slowing the conversion of urea into ammonia, reducing volatilisation losses following application, while nitrification inhibitors slow the conversion of ammonium into nitrate, reducing the risk of leaching under certain soil conditions. Both influence biological or chemical reactions occurring within the soil and in essence do not slow or control the release of nitrogen from the urea granule. Controlled Release Technology takes a physical approach instead. The nitrogen remains enclosed until the membrane allows it to diffuse into the surrounding soil, meaning the release profile is determined by the coating itself rather than by modifying soil chemistry.

Achieving that level of control depends heavily on polymer engineering. The membrane must be thin enough to allow consistent diffusion, yet durable enough to withstand manufacture, transport, storage and spreading through conventional fertiliser equipment without cracking or damaging the coating. Uniformity is equally important. Every granule must receive a consistent coating thickness to ensure the fertiliser behaves predictably across an entire paddock. Even small variations in coating thickness can alter nitrogen release rates, creating uneven nutrient availability and inconsistent crop performance.

The release profile can also be engineered for different farming systems. By adjusting coating characteristics, the duration of nitrogen release can be altered to suit pasture, forage crops or arable production. Rather than applying nitrogen that becomes immediately available over a matter of days, Controlled Release Technology can extend nutrient availability across several weeks or months, more closely matching the period over which actively growing plants require nitrogen. This ability to engineer different release curves is one of the defining characteristics of modern controlled-release fertiliser systems.

For forage producers, that engineering has practical implications beyond the laboratory. Silage crops, maize, and intensive pasture systems all have periods of rapid nitrogen demand followed by slower uptake. Conventional urea delivers the majority of its nitrogen shortly after application, meaning weather conditions during the following few days largely determine how efficiently that nutrient is captured. Heavy rainfall can increase losses through leaching, while warm, dry conditions immediately after spreading can increase volatilisation. Controlled Release Technology reduces the dependence on those narrow weather windows by regulating the rate at which nitrogen becomes available beneath the soil surface.

The technology also provides greater flexibility around application timing. Contractors are increasingly working within compressed seasonal windows where fertiliser spreading, cultivation, drilling, mowing and harvesting frequently overlap. A fertiliser designed to deliver nitrogen over an extended period potentially reduces the need for repeat applications while giving operators greater flexibility when weather interrupts field operations. That does not remove the need for sound nutrient management, but it does provide another management tool within increasingly complex production systems.

Tnue has applied this technology across a growing product range. Its controlled-release nitrogen fertiliser uses polymer-coated urea to provide sustained nitrogen availability, while Dual-Start combines immediately available phosphate with two distinct nitrogen release profiles. Approximately 30% of the nitrogen is available soon after application to support early crop establishment, with the remaining 70% released progressively over around 90 days. The objective is to provide both immediate plant response and sustained nutrient supply from a single application, reducing the mismatch that often occurs between conventional fertiliser release and crop demand.

The company also offers customised fertiliser blends incorporating controlled-release nitrogen, allowing nutrient programmes to be tailored to individual crop requirements. This reflects a broader trend within precision agriculture where fertiliser is increasingly being designed around crop demand curves rather than relying solely on standard commodity products.

Behind the product sits more than a decade of research and development undertaken in New Zealand. Commercial production now takes place at Tnue's manufacturing facility in Taupō, where the coating technology has been scaled from laboratory development to commercial manufacture. Maintaining coating consistency at production scale is one of the less visible but more technically demanding aspects of controlled-release fertiliser manufacturing. Every stage, from polymer application through to curing and quality assurance, influences the uniformity of the final product and ultimately the consistency of nitrogen release in the field.