Researchers at Universidad Nacional de Colombia build an affordable system to detect plant nutrients

According to the Colombian Corporation for Agricultural Research (Agrosavia), just 15 % of the country's farmers might be approaching the use of sensors, data analytics and digital farming tools to maximize crop yields and optimize their farming resources.

“Affordability and accessibility to cutting-edge tools are still limited in the country. In farming operations, it is key to reduce any risk related to late detection of plant nutrient deficiencies, unseen plant diseases or poor crop quality. Those ideas inspired the decision to develop optical, non-destructive and in farm usable portable plant analyzers", says Juan Carlos Pérez Naranjo, a professor at the Faculty of Sciences of the Universidad Nacional de Colombia (UNAL) Medellín Campus.

It is estimated that colombian farmers overuse 70 to 80 kg of nitrogen and phosphorus fertilizers in each hectare of land being cropped. This might be due to the low access to new and affordable measuring instruments. "We then conceived a multispectral camera, which sequentially use LED lights to illuminate plant samples and then make pictures. These samples can comprise leaves, fruits, stems or roots. Plant nutrient or plant general status can then be inferred from an automatic analysis of these images. Even though these are very expensive and complex devices, said the researchers”.

Building one of these systems involved carrying out many controlled agricultural experiments, electronic circuit design and computer language programming, so this work was a true multidisciplinary one. "We started with optics and physics concepts, and set out to use cheap materials from the shelves such as a U$4 webcam or cheap initial optical integrating spheres made from inflatable globes hardened by external medical plaster bandages. The recipe to freely build this refined desktop multispectral camera, including control software, hardware and electronics is already published as an open system. We hope it to be freely reproduced anywhere in the world and is called Medusa, to stand for the initial appearance of the excessive wiring needed to make the first models", adds Daniel Mauricio Pineda Tobón, Master of Science in Physics and currently a PhD candidate in Engineering - Systems and Computer Science at UNAL Medellín Campus.

The magic of light: Just think in chlorophyll

Light can be understood as energy that comes as the colors perceived by human eyes. "Every surface we see reacts in a particular way to that energy: a table, paper, our skin, and we perceive those differences as colors. The same happens with plants, the different types of light – ultraviolet, infrared, etc. – reacts in a different way according to its tied chemical properties", explains Mr. Pineda.

Chlorophyll, for example, is directly related to the nitrogen content in leaves, so its concentration can be used as a criterion for whether or not to apply certain crop fertilizers. "Initially we designed a system to measure only chlorophyll based on the transmission of red light through plant leaves, and for that we built it in such a way that only a LED with 660 nm emission and a smartphone ambient light sensor would be needed", he continues.

The researchers tested the Medusa system, consisting of a camera, 18 LED lighting module and control software to illuminate and see the hidden differences in plant nitrogen leaves, the invisible ripening or damages in avocado fruits, fake and authentic bills, and even eye undetectable bacteria cultures. "This device can easily show anybody its great potential. And it can be freely improved by any user If better quality cameras and wider spectral range LEDs are used", says professor Pérez.

In a specific local application, leaf nitrogen content was estimated on dried ground samples of bananas, chrysanthemums, cocoa and rubber leaves, to get results comparable to those obtained from a more complex, lengthy, highly contaminating and expensive commercial standard system called Kjeldahl leaf nitrogen analysis. "Medusa, the multispectral camera performs very well despite the general differences due to the apparent chlorophyll content and texture among these plant species", adds professor Pérez.

These results demonstrate that it is possible to custom build in the country cutting edge economical equipment that will impact teaching, research and general agricultural development. "In addition, the device has the potential to be used without having specific knowledge of electronics or programming, which will also democratize general access to new technologies. The only important point would be to calibrate it for use in general plant nutrient diagnostics under a specific scenario of plant cropping", concludes the professor.