In a year when margins are tight it’s going to pay to make maximum use of every kilo of nitrogen applied by keeping it in the soil and available to the plant.

Early nitrogen fertiliser applications are often poorly synchronised with early-season plant demand, leading potentially to significant nitrogen losses through leaching or volatilisation, says Joel Williams of Integrated Soils.

While use of synthetic chemical inhibitors is effective at reducing losses by slowing production of ammonia and nitrates – the latter of which can be converted and lost as nitrous oxide in anaerobic conditions – adding a carbon source to nitrogen applications can produce the same effects, with some additional benefits, he says.

“The core benefit of adding a carbon source, such as humic or fulvic acid, or molasses is stabilising nitrogen,” he explains. “The carbon acts as a sponge that binds the nitrogen, making it a larger molecule and changing its behaviour so it’s less likely to leach.

“The carbon wraps around the nitrogen, which also slows down off-gassing or volatilisation of both ammonia and nitrous oxides.”

David Maxwell, sales director for QLF Agronomy, says that the molasses-based fertiliser L-CBF BOOST contains added fulvic acid, and naturally occurring humates, which is the solid form of humic acid.

A second part of the mechanism, which is specific to molasses products such as L-CBF BOOST, is the provision of a food source for soil biology. “Molasses provides highly digestible sugars for microorganisms in the soil,” he says.

“Rather than providing a carbon sponge in which nitrogen is stored before being released more slowly, the molasses stimulates the biology to eat the fertiliser and then store it in their bodies, by converting it into amino acids and proteins.”

While nitrogen is temporarily tied up, as organisms grow and die and excrete waste products, it is slowly released.

“50% of soil organic matter is made up of dead soil microorganisms,” adds David.  “They’re critical for good soil health.

“Adding a carbon source with nitrogen fertiliser allows soil to immobilise some available nitrogen and release it slowly into the soil as the microbes break down. The result is mineralised nitrogen available to the plant as it needs it, following the initial nitrogen spike when fertiliser is applied.

Joel continues: “This provides better synchronisation between the supply of nutrients and the demand of the plant, especially in spring when we have smaller plants with smaller demands for nitrogen.

“Typically, we apply larger doses relative to the demand of these smaller plants, and it’s that lack of synchronisation that creates the opportunities for losses to occur.”

Using a carbon source is more effective and practical in liquid fertiliser systems than in solid systems, he says.

Understanding better how the use of carbon sources with fertilisers compares with synthetic inhibitors is the aim of a literature study Joel is currently undertaking for QLF Agronomy.

“We have good data showing that carbon additives have urease inhibition effects, can reduce ammonia volatilisation, lower losses from nitrous oxide and leaching.

“I’m currently studying how the two compare, but it’s clear that using a carbon source has other benefits which chemical inhibitors won’t provide,” he says.

For a copy of the literature study when it is ready, email: web@qlf.co.uk