US researchers test a sensor to assess nutrient loss

A research project at the University of Missouri describes the potential of a new instrument to detect the presence of phosphorous- and nitrogen-based nutrients in the soil. An innovation that would pave the way for a more sustainable use of fertilisers

by Matteo Cavallito

 

The loss of nutrients in the soil has always posed a significant threat to farmers. That’s why researchers at the University of Missouri are currently experimenting with a new tool to monitor the phenomenon while providing the most useful information to mitigate it.

The scientists, led by Matthias Young, a researcher at the same US university, are focusing in particular on nitrates and phosphates, i.e., those nitrogen– and phosphorus-based substances that play a fundamental role in ensuring soil fertility. The research team, explains a statement, is now aiming to develop new types of sensors to help farmers better measure the presence of nutrients, enabling them to use fertilisers more efficiently.

The dangers of nutrient leakage

Nutrients are indispensable components of soil health. Their dispersion outside of crops, therefore, inevitably generates economic and environmental damage. ‘Based on data from the Environmental Protection Agency and the United States Department of Agriculture, an estimated $100 million of fertilizer is wasted every year in Missouri alone,’ Young points out. As for the environment, these are known to have wide-ranging effects.

‘Nitrates and phosphates released into waterways cause algae blooms that kill fish and hurt tourism in waterfront communities,’ the researcher adds.

In addition to damaging water quality, excessive nitrates can cause eutrophication (the over-enrichment of nutrients) and pose health risks to animals and humans. And the problem, the authors explain, is that when knowledge about the actual availability of nutrients is limited, farmers can be induced to misuse fertilisers. Which results in under-use or, conversely, over-use.

The limitations of available instruments

At the moment, farmers have at their disposal special devices, known as ion-selective electrodes, which are able to measure the presence of nitrates and phosphates. These instruments, however, are expensive and inaccurate, the researchers explain. Alternatively, soil samples can be collected and sent to specialised laboratories with more sophisticated technology. Even this system, however, is particularly expensive and, at the same time, risks providing information limited to a circumscribed part of the soil.

For these reasons, Young and his collaborators are trying to develop portable sensors ‘to collect measurements in real-time, as well as sensors that can be installed in the field’. The instruments, he adds, are not yet ready but promise to offer new opportunities. How? By providing a faster, more reliable and cheaper way to measure relevant ions such as nitrates in the soil.

A new system

The results obtained so far were presented in an article published in ACS Omega, a publication of the American Chemical Society. The subject is quite complex, but the basic principle can be summarised as follows: unlike its predecessors, the sensor that Young and the research team are developing does not measure the force with which ions bind to a membrane, but rather the speed with which they cross it. Using a pulsed direct current would also make the devices more sensitive and reliable.

‘Using PVC-based ion selective membrane (ISM) containing a nitrate ionophore (NIVI), we demonstrate that pulsed current provides the benefits of (1) > 100 times thinner ISE membrane layers, (2) > 10 times faster measurement, and (3) simpler construction without the need for a chemical reference electrode,’ the study says. The hope of the researchers is to complete the development of the sensors for subsequent commercialisation.