Smart fertilisers for food security

By 2050, we will need to feed a population of ten billion people, which is around 70 per cent more food than we currently produce.

Factoring in the added challenges of climate change and ecosystem degradation, how can this extra food be produced without further damage to the natural environment?

Crops – be they grains, cereals, fruits or vegetables – are integral to human food security given that they’re eaten directly as well as fed to animals.

So, one key potential improvement is to increase fertiliser efficiency – particularly nitrogen (N) fertilisers – by using the right amounts of N when and where plants need it and finding ways to reduce N losses to the environment.

Currently, N fertilisers are used to produce half the world’s food supply. However, 50 to 80 per cent of N applied to crops is lost from production, polluting the natural environment in the form of nitrous oxide and ammonia emissions into the atmosphere as well as nitrate leaching and runoff to groundwater and waterways.

Nitrogen pollution also causes loss of biodiversity, contributes to global warming, depletes stratospheric ozone, damages human health and imposes economic costs.

DESIGNING SMART FERTILISERS

Enhanced-efficiency fertilisers (EEFs) exist but have not been adopted widely because of inconsistent performance across soils, crops, and climates, and uncertainty about economic benefits.

In 2021, the ARC Research Hub for Innovative Nitrogen Fertilisers and Inhibitors (Smart Fertilisers) was founded to overcome the limitations of existing EEFs.

The Hub is a partnership between leading researchers and industries to deliver next-generation EEFs that increase the efficiency of nitrogen use by up to 20 per cent. The partnership will also develop decision-making tools to assist farmers in reducing costs and nitrogen loss to the environment.

In pursuing major breakthroughs in the design and development of EEFs, the Hub takes a multidisciplinary approach, integrating agronomy and soil science with synthetic chemistry, chemical engineering, plant physiology, plant biochemistry and economics.

A primary research focus is engineering new fertiliser coatings for the controlled release of nutrients and inhibitors in a range of soil types, climatic conditions and diverse agroecosystems and land uses.

Granular urea is the most widely used form of N fertiliser in agriculture. Urea is rapidly converted to ammonia through a reaction with water in the soil, and subsequently to nitrate, that plants take up.

However, if the conversion to ammonia occurs before urea is fully dissolved in the soil, ammonia is lost to the atmosphere before the plants can use it.

A recent study that included researchers from the Smart Fertilisers Hub showed that Metal-Phenolic Networks (MPNs) can provide a physical barrier against water, controlling the dissolution of urea and its release into soil reducing the risk of N losses.

This simple MPNs fabrication method is a new chapter in creating environmentally-friendly materials in controlled-release fertilisers.

Another research focus is on the development of a new suite of inhibitors, which are small synthetic molecules that slow the conversion of urea to ammonia by inhibiting the activity of the enzyme urease (urease inhibitors) or slowing the microbial autotrophic oxidation of ammonia to nitrite and nitrate (nitrification inhibitors).

The aim is to retain desirable forms of N in the soil for the plant and limit N losses.

These new inhibitors will be tailored to different soils, climates and cropping systems, at the same time ensuring that their eventual degradation in the soil is environmentally benign.

‘LISTENING’ TO PLANTS

The soil immediately around plant roots – the rhizosphere – is an especially active zone populated by billions of fungi, bacteria and other microbes.

These microorganisms break down organic matter in the soil to produce nutrients that plants can use for growth and help plants to improve immunity and promote resistance to drought, salinity and N stresses.

Research shows that plants can influence how fungi and bacteria behave by sending chemical signals like sugars, organic acids, lipids and proteins, especially when lacking a specific nutrient or under stress.

These messengers can be identified and incorporated into the coatings of fertiliser beads. Beneficial microbes are then attracted by these messengers to the plant root, improving the absorption of N and promoting the resistance of a crop to environmental stresses.

EEF coating can also be designed to include sensors that respond to the signalling molecules released by plants suffering from N stress. When the sensors detect these stress molecules in the soil, the fertiliser is then released via the coating.

COSTS AND BENEFITS OF SMART FERTILISERS

Farmers adopting new fertilisers need evidence of their consistent performance across soils, crops and climates as well as information about likely net benefits.

Wider adoption of next-generation EEF technologies hinges on demonstrating the net benefits to farmers, which requires sharing relevant and plausible information to farmers and their networks.

The Smart Fertilisers Hub team analysed the results of 21 meta-analyses about the potential of EEFs to reduce N losses from food production systems, at both regional and global scales.

This data shows that EEFs show a lot of promise for reducing N losses from agricultural systems. Considering the immense social costs associated with N pollution globally – US$200−2000 billion each year – EEFs have great potential to reduce these social costs.

POLICY IMPLICATIONS

By measuring the N loss pathways and yield benefits of existing and newly developed products in field trials, the agronomic, environmental and social benefits of the new fertiliser technologies developed by the Hub can then be evaluated.

The Hub will develop indicators of N losses to allow farmers to understand the full impact of their fertiliser management practices on their production and on the environment.

The team will map the potential benefits of new fertilisers, identify sources of added benefit in commercial value chains, while informing farmers and consumers about the usefulness of products grown using EEFs.

Smart fertilisers minimise the social and environmental costs of N pollution, a benefit that will far outweigh the economic cost and a more efficient approach than cleaning up environmental damage afterwards.

Sound policies that lead to the adoption of smart fertilisers are vital to achieving food security and environmental health for our growing population.

The ARC Research Hub for Innovative Nitrogen Fertilisers and Inhibitors (Smart Fertilisers), launches on 21 October 2022. The Hub’s $AU11.35 million funding includes an investment of $AU4.95 million from the ARC, $AU3.8 million from Incitec Pivot Fertilisers, $AU2 million from the University of Melbourne, $AU100,000 from La Trobe University and $AU500,000 from Elders Rural Services Australia.

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