Slow release fertiliser can revolutionise agriculture: scientists

Sri Lankan scientists have developed a simple way to make a benign, more efficient fertiliser that could contribute to a second food revolution, it is claimed.

The nanoparticle-based “slow release” nitrogen fertiliser they have successfully tested in rice fields can simultaneously cut down the emission of greenhouse gas associated with agriculture, they report in the American Chemical Society journal ACS Nano.

Nitrogen is an essential nutrient for crops. Urea is a rich source of nitrogen and so farmers currently use it to fertilise the soil. But urea breaks down quickly in wet soil, resulting in the evolution of ammonia before it can be efficiently adsorbed by the plants.

This ammonia gets washed away, creating a major environmental issue as it leads to eutrophication (over-enrichment) of waterways. It eventually enters the atmosphere as nitrogen dioxide, the main greenhouse gas associated with agriculture that contributes to climate change.

The fast decomposition of urea also limits the amount of nitrogen that can get absorbed by crop roots and currently requires farmers to apply more fertiliser to boost production — thus adding to the cost.

The researchers, says the report, wanted to find a way to slow the breakdown of urea and make one application of fertiliser last longer.

To do this, they developed a simple method for coating “hydroxyapatite nanoparticles” (HA-NP) with urea molecules. Hydroxyapatite is a mineral found in human and animal tissues and is considered to be environmentally-friendly while itself acting as a rich phosphorus source.

According to the report, the incorporation of urea into a HA-NP matrix reduced the solubility of urea in water, thus preventing its rapid breakdown into ammonia.

“The high surface area offered by the nanoparticles allows binding of a large amount of urea molecules. This nanohybrid with a nitrogen weight of 40 per cent provides a platform for its slow release,” the researchers say.

The slow release of urea from this nanohybrid leads to a reduction in the rate of urea decomposition in soil, therefore leading to higher nitrogen-use efficiency of plants, they say.

According to the report, field tests on rice farms, carried out for three seasons, showed that the HA-urea nanohybrid halved the fertiliser needed.

The researchers say their development could help contribute to a new green revolution and also improve the environmental sustainability of agriculture.