Sensors help with efficient fertiliser use

Ensuring food security for the world’s population depends to a large extent on efficient fertiliser-based agriculture. Recently, however, the price of fertiliser has more than tripled since the start of the war in Ukraine. As if the problems of supplying this product weren’t enough, there are also concerns about the environmental effects of fertiliser production, which consumes a lot of energy. At a global level, the process to produce the ammonia used in fertilisers uses around 1% of all fossil fuels and produces 1% of all carbon dioxide emissions. How can this dilemma be overcome?

A new technology proposed by the Technical University of Munich (TUM) wants to help facilitate fast, easy and precise fertilisation in the future. The solution uses a combination of biosensor strips and data collected via satellite, the method will be able to determine the nutritional conditions of cereals and the ideal volume of fertiliser to be used. Digital analytical data is sent to the tractors, preventing over-fertilisation and also saving time.

The researchers compare the method with blood glucose tests. Plant stems are collected from at least three different locations in the field. A drop of sap from these stems on a test strip is enough to measure the nitrate content with a small device.

The test result is available in a few minutes and is used to calibrate the remote sensing data that is already available via satellite from the European Union’s Copernicus programme, Europe’s earth monitoring service. The combination of precise local measurements and widely available Earth observation satellite data allows for the exact calculation of the volume of nitrogen fertiliser needed in the field in question.

TUM researchers estimate that the method will save up to 20% of the fertiliser needed to grow cereals.

According to Germany’s Federal Environment Agency, 50% of the nitrogen fertiliser used in agriculture in the country is not absorbed by plants. Excessive amounts of fertiliser remain in natural environments and have an impact on soil and water. Most of the time, calculations of fertiliser to be used on crops are made purely by mathematical equations with standardised parameters or based on experience. In addition, although it is possible to determine the nutritional conditions of plants by means of laboratory analyses, this is still very costly in terms of time and money. It has therefore been almost impractical for use in the field to date.

The initial focus of TUM’s research is the supply of nitrogen to cereal crops. In the future, they plan to test the nutritional status of plants based on phosphate and potassium. Prototypes of the new TUM diagnostic method should be available for purchase in the future. The researchers estimate that it will cost around 20 euros per hectare to use the new technology.

Field tests of the new technology will begin later this year. Collaboration with regional machinery suppliers is giving TUM researchers the chance to gain experience with input from various users. The results of the practical tests will be incorporated into the new method over the next three years.

For this research project on the precise and efficient use of fertilisers, TUM received a grant from the European Innovation Council (EIC), which offers financial support to researchers of innovative technologies for sustainable agriculture.

Sensors on the ground

In the United States, at Pennsylvania State University (Penn State), researchers have developed a multi-parameter sensor capable of decoupling temperature and nitrogen signals so that they can accurately measure soil conditions and thus help farmers achieve optimum fertilisation levels for crop growth.

“Plant growth is also affected by temperature, which influences physical, chemical and microbiological processes in the soil. Continuous monitoring of these conditions allows farmers to develop strategies and interventions when temperatures are too high or low for crops,” explains Li Yang, co-author of the study and professor at the School of Artificial Intelligence at Hebei University of Technology in China.

However, both gases and temperature, as well as variations in relative humidity, can cause changes in the reading of the sensors, which are unable to differentiate between these quantities. Mechanisms for independently measuring nitrogen gas and temperature are difficult to find, according to the researchers. To overcome these limitations, the team designed a high-performance multi-parameter sensor to decouple the readings of temperature and nitrogen loss from the soil. “The ability to simultaneously detect ultra-low nitrogen oxide concentrations and small temperature changes paves the way for the development of future multimodal electronic devices with decoupled sensing mechanisms for precision agriculture, health monitoring and other applications,” says Huanyu Cheng, Associate Professor of Engineering Science and Mechanics at Penn State.