Berkshire, England: Slow and controlled-release fertilisers reduce the speed of release of plant nutrients from fertilisers to the plant. This can be achieved by different means.

With controlled-release fertilisers, the principal method is to cover a conventional soluble fertiliser with a protective coating (known as encapsulation) of a water-insoluble, semi-permeable or impermeable with pores material.

This controls water penetration and thus the rate of dissolution, and ideally synchronises nutrient release with the needs of a plant.

“The use of controlled-release fertilisers has increased over recent years, not just due to the environmental benefits that they give, but also for the economic and time-saving attributes,” said Brian Croose, Asean Regional Manager for Indigrow, a Full Business Member of the Asian Golf Industry Federation.

“These specially formulated fertilisers are available with several technologies, one of which is the Polymer Sulphur Coated Urea (PSCU) coating used in the Impact range,” he added.

Indigrow’s PSCU fertilisers are a hybrid of both sulphur and polymer options.

The sulphur is applied initially as a thinner layer, reducing the chances of ‘lock off’ which occurs when the coated granule fails to release its nutrients, more prevalent when the sulphur coating is too thick.

The granule is then coated with a polymer. This reduces the potential of catastrophic ‘burst’ (premature release of nutrient), prevalent in sulphur coated urea products due to imperfections in the coating.

The PSCU coatings can be built up in layers. The overall thickness dictates the longevity and diffusion rate, which is dependent on moisture. As the layers of polymer increase, this extends the release time.

The longevity is regulated by moisture which is highly correlated with nutrient availability and uptake. This ensures that when water availability initiates gradual breakdown of the polymer coat, the osmosis increases the internal pressure on the inner pool of nutrient, slowly releasing the nitrogen to the rhizosphere.

Nitrogen losses occur in many ways. Controlled-release fertilisers can reduce volatilisation by ensuring the urea fertiliser is intact, not broken down by urease enzymes.

These can cause volatilisation of ammonia gas via ammonium carbamates conversion to ammonia and carbon dioxide if there is inadequate moisture. The coating breakdown releases the urea once sufficient moisture is available for the conversion of ammonia gas to ammonium ions which then, due to their positive charge, are attracted to the soil cation exchange complex.

The PSCU range is a major part of most turf managers’ armoury when trying to maintain quality aesthetics for long periods under time constraints.

Longer periods between applications ensure that the playing surface is available more regularly to the clubs, due to the reduced number of applications required to maintain the same nutrient input.

Croose said: “Our range of products contains coating from as low as 20% to as high as 93% inclusion, giving an expected release period from eight to 24 weeks, depending on the coating level.

“The range of longevity options allows for flexible medium and long-term management whilst not demanding frequent allocation of time.”

The graph below shows how the different inclusion levels on Indigrow’s CGF range of fertilisers release their nutrients over time, comparing them against a conventional release agricultural fertiliser.