Is zinc the secret to replenishing soil nutrients?

Researchers from Aarhus University in Denmark, in collaboration with Polytechnic University of Madrid, and European Synchrotron Radiation Facility in France, have found that zinc significantly influences the nitrogen fixation process in legumes. And what’s more, they believe this discovery could transform legume-based agriculture and crops grown on land under crop rotation.

Farmers have increasingly been struggling with the effects of nutrient depletion in soil. Intensive farming, implemented to meet the increasing demand of a rising population, has put agricultural soil under strain.

Exacerbating this problem is the fact that fertiliser prices have risen sharply​ in recent years, making the replenishment of nutrients more costly. As a result, nutrient depletion in soil is becoming a major issue and poses a significant threat to food security.

“Healthy soils are essential for achieving climate neutrality, a clean and circular economy and stopping desertification and land degradation,” said a spokesperson for the European Commission. “They are also essential to reverse biodiversity loss, provide healthy food and safeguard human health.”

However, there is an argument to suggest that farming systems should not be so reliant upon fertilisers to nourish the soil. According to the Soil Association, the overuse of fertilisers can result in nitrogen pollution, which occurs when some nitrogen compounds, such as ammonia and nitrous oxide, become too abundant. The United Nations has also warned of the potential health implications of excessive and inefficient fertiliser use, saying it could cause issues such as, “drinking water contamination and eutrophication of freshwater systems and coastal zones.” The UN also stated that some fertilisers can, “impact human life due to unsafe storage practices.”

And this view is supported by organisations across the globe, which are urging farmers to adopt regenerative agriculture​ practices.

“Regenerative agriculture is the way forward to decarbonise the food system and make farming resilient to climate shocks,” said a spokesperson for the World Economic Forum. “Regenerative farming on 40% of the world’s cropland would save around 600 million tons of emissions. This is around 2% of the total, equivalent to the footprint of Germany.”

This knowledge has led scientists and farmers to look for ways to protect and restore soil health, without relying on fertilisers. And they think zinc could be the answer.

What is regenerative agriculture?​While no official definition of regenerative agriculture exists in the EU, it’s generally understood the term refers to principles that protect and support the surrounding environment.

These include:

1.         Minimising soil disturbance

2.         Maximising crop diversity

3.         Keeping soils covered

4.         Maintaining living roots year round

5.         Integrating livestock

How can zinc support soil health?​Climate change, drought, increased temperatures, and intensive farming is causing stress to soils and threatening agricultural sustainability. The research team specifically looked at ways to alleviate those stressors and found that zinc plays a pivotal role in a plant’s response to abiotic, or physical, stress. And in doing so, they found that zinc plays a vital role in the nitrogen fixation process of legumes.

The researchers are confident that this discovery, paired with insights into the transcriptional regulator known as ‘fixation under nitrate’ (FUN), has the potential to transform legume farming by enhancing crop efficiency and decreasing dependence on synthetic fertilisers.

What are legumes?​Legumes are a type of grain, grown primarily for human and livestock consumption. Though they are also grown for use in soil-enhancing green manure​.

Well-known legumes include beans, chickpeas, peanuts, lentils, lupins, mesquite, carob and tamarind.

Legumes are notable for the symbiotic nitrogen-fixing bacteria in their root nodules. This nitrogen-fixing process makes them an ideal crop in restoring soil nutrients and an important crop for crop rotation.

Examples of legumes include beans, chickpeas, peanuts, lentils, lupins, mesquite, carob and tamarind. GettyImages/MEDITERRANEANWhat is the nitrogen fixation process?​Nitrogen fixation is the process by which nitrogen is taken from its molecular form (N2), in the atmosphere, and converted into nitrogen compounds useful for other biochemical processes.

What is a transcriptional regulator?​Transcriptional regulation is the means by which a cell regulates the conversion of deoxyribonucleic acid (DNA) to ribonucleic acid (RNA), thereby orchestrating gene activity.

The team found that legumes use zinc as a secondary signal to integrate environmental factors and regulate nitrogen fixation efficiency. They discovered that fixation under nitrate is a novel type of zinc sensor, which decodes zinc signals in root nodules, and regulates nitrogen fixation.

“It’s truly remarkable to discover zinc’s role as a secondary signal in plants,” says assistant Professor Jieshun Lin. “It is a vital micronutrient, and it has never been considered as a signal before. After screening over 150,000 plants, we finally identified the zinc sensor FUN, shedding light on this fascinating aspect of plant biology.”

How could zinc in legumes benefit other crops?​Farming legumes could benefit farmers through the improvement of soil for all crops. Increasing nitrogen availability in the soil would not only benefit legumes grown, but also co-cultivated crops and any future crops grown in that soil.

The researchers hope that this understanding will lead to future research that provides new ways to manage farming systems, reducing the use of nitrogen fertiliser and its impact on the environment. It could also help to support more sustainable and resilient food systems​.

The implications of this research are significant. By understanding how zinc impacts nitrogen fixation, farmers could benefit from increased crop yields and reduce the need for synthetic fertilisers, which have environmental and financial implications.

Source: Zinc mediates control of nitrogen fixation via transcription factor filamentation
Published online: 26 June 2024
DOI: https://www.nature.com/articles/s41586-024-07607-6
Authors: Jieshun Lin, Peter K. Bjørk, Marie V. Kolte, Emil Poulsen et al.