To increase soil fertility, it is common for farmers to use more fertiliser than crops actually need. While this approach helps ensure a good yield, it has negative economic and environmental consequences.

One answer would be for farmers to have access to accurate and timely information about the amount of nitrogen available in the soil, to adjust their inputs accordingly. However, the take-up of existing analytical tools is poor because of costs and the laborious workflow relying on laboratory analysis.

The approach of the LiveSEN (In-Field Live Sensing of Nitrate in Crops for Real-Time Fertilization Adjustment) project, supported by an ERC Proof of Concept grant, was to measure nitrate levels directly from plant juice. This liquid sample not only simplified sample preparation, but also crucially made on-site analysis possible with single-use electrochemical biosensors.

Validation experiments were performed in the lab, with the team now upscaling fabrication of the sensors. They are fine-tuning the inkjet printing process for enzymes deposition while looking for a manufacturer of screen-printed electrodes (SPE) to develop automated mass production plans. As well as being costly, current analytical tools (such as nitrate ion-selective electrodes) are not single-use and so have to be cleaned between measurements and need frequent calibration. As they are also sensitive to different ions, their readings on complex samples (such as plant juice) can be inaccurate.

“We wanted to develop an on-site biosensor for immediate information about how much fertiliser a plant needs, usable without training, to bypass the need for technicians or expert consultants for sampling, measuring, data interpretation and decision making,” says Nicolas Plumeré, professor at Ruhr University Bochum, who led the LiveSEN project.

In the project, the biosensor uses enzymes to detect nitrates which react with the electrode’s electrons. The number of these electrons is measured to quantify the number of nitrate molecules present in the plant juice. The biosensor also incorporates systems to avoid interference (patent pending), including enzymes (oxidases) for removing dissolved oxygen which would otherwise also accept the electrons, giving a false reading.

The recommended nitrogen input is then provided immediately to farmers through a smartphone app connected to a cloud-based system.

“Farmers gave us feedback about the practicalities of using a high-tech device in all weather, possibly while operating farm equipment. This helped us redesign around their needs. They also flagged other priorities, such as phosphate and sulfate content, for which we are developing a similar sensor,” says Plumeré.

The LiveSEN project will use Big Data to generate fertilisation recommendation maps from a combination of biosensor data, weather information, topographic information and multispectral satellite images (chlorophyl or ‘greenness’ maps of fields) from the EU’s Copernicus project. This means fertilisation can be adjusted within a field, satisfying a crop’s nutrient needs.

Improving environmental management

LiveSEN’s work is in alignment with the EU’s Declaration of cooperation on ‘A smart and sustainable digital future for European agriculture and rural areas’. Furthermore, it will allow individual farmers, as well as national bodies, to meet the criteria set by the EU Nitrates Directive (91/676/EEC).

Farmers will be provided with the sensors at production cost, enhancing the accuracy of Big Data prediction modelling. The LiveSEN package will then offer a paid-for fertilisation recommendation service through a smartphone or computer app.

“Our idea could increase agriculture yields by 5 to 10 %, reducing costs and pollution, especially CO2 emissions; with the production of nitrogen fertilisers accounting for over 1 %,” says Plumeré.

Biography

The research group of Nicolas Plumeré at the Ruhr-University Bochum, Germany develops electrochemical concepts in sustainability. He was awarded the prestigious ERC Starting Grant in 2016 on novel approaches for integrating highly active catalysts in energy converting schemes, followed by an ERC Proof-of-Concept Grant in 2018 on field sensors for precision agriculture.