Ornamental plant cultivation is locally anchored in almost all German districts, mainly with small and medium-sized farms. In 2022, the production value of flowers and ornamental plants produced in Germany amounted to around 1.2 billion euros. Sales of cut flowers, for example, amounted to around 3.1 billion euros.¹ In order for the plant cultivation sector in Germany to remain competitive, it is dependent on secure and high yields. Decisive factors for this include successful plant breeding, plant protection and optimal fertilization in order to conserve resources and soils.

In the ZierSens project, the Fraunhofer FEP conducted research into a technology that can detect deficits or nutrient surpluses in ornamental plants at an early stage. The institute has decades of experience in the development of application-specific OLED microdisplays for a wide variety of purposes. It is also possible to combine OLED light sources and photodiodes on a silicon chip. So-called bidirectional microdisplays are thus able to emit and simultaneously detect light in a wavelength-specific manner.

This technology enables the measurement and evaluation of small areas for surface inspection in various fields of application. In the project, it was specifically used to detect the condition of an ornamental plant with regard to possible under- or oversupply. With the help of a mechanism a leaf of an ornamental plant is pressed onto the microdisplay, which illuminates the leaf and can detect and evaluate the reflected light. In extensive plant cultivation experiments at the LfULG, plants were prepared in different nutritional states and images of leaves at different stages were taken. These images were used to train artificial neural networks to automatically identify leaf characteristics.

Compared to conventional measuring systems, which require a large number of measurements and use an averaged value within the measuring spot, bidirectional OLED microdisplays offer a location-resolved measurement. This allows several measured values to be generated at one measuring point, which are directly related to each other. This should enable more targeted fertilization and thus a more efficient use of resources, thereby reducing the environmental impact.

Judith Baumgarten, project manager at Fraunhofer FEP explains: "The project was based on the hypothesis that a lack or excess of nutrients can be detected at an early stage by the smallest changes in leaf coloration. By using our bidirectional microdisplay technology, we have achieved various effects that do not disprove this assumption, but also do not yet confirm it 100%. Nevertheless, we were able to further develop the measuring system and lay the foundations for the evaluation of colored camera images. We see great potential for the plant cultivation of the future with the support of smart technologies." Head of the Ornamental Horticulture Department and project manager at the LfULG, Dr. Sven Schubert, adds: "The use of modern technologies is essential for resource-conserving and sustainable horticulture. The data collected in the plant cultivation trials form the basis for the further development of sensor technology."

In addition, the scientists have trained neural networks to identify the plant species, leaf side and leaf age of the ornamental plants used. A further neural network was also developed to automatically segment the images into the areas of leaf area, leaf vein, leaf pattern and defects.

Research into the new technology presented the Fraunhofer FEP with a number of challenges. Firstly, adequate imaging of leaves with a special topology, such as primroses, was required, which necessitated further optimization of the sensor hardware. Secondly, models had to be created for evaluation, which would require a very large neural network due to the different characteristics of the plants. This would mean that calculations could no longer be performed on mobile devices, as is necessary in smart crop production. The Fraunhofer FEP is therefore pursuing a cascaded approach with several smaller networks that require significantly fewer resources.

The Fraunhofer FEP researchers see great potential in this proof-of-concept for plant breeding and ornamental plant cultivation and will present first project results and microdisplay technologies at the W3+ Fair, in Jena, from November 29 – 30, 2023, at booth no. C12.

¹ Sources: Statista: https://de.statista.com/statistik/daten/studie/206586/umfrage/umsatz-im-zierpflanzenbau-nach-pflanzenarten/ and https://de.statista.com/statistik/daten/studie/206586/umfrage/umsatz-im-zierpflanzenbau-nach-pflanzenarten/