The pocket-sized tool supporting farmers for 30 years

“The N-Tester brings clarity to nitrogen management and helps farmers reach their yield and quality goals. It delivers practical decisions backed by science and grounded in what the plant shows on that very day.” 

Gustavo Portz R&D Lead Agronomic Decision Support and Digital Tools at Yara Agronomic Research and Development (YARD)

Where it all began

Back when precision agriculture was still an idea taking shape, Dr. Jürgen Wollring and his team at Yara’s Hanninghof research center imagined a simple device that could bring plant science directly into farmers’ hands.

They pictured a device capable of reading chlorophyll levels from a leaf and turning those measurements into fertilizer recommendations tailored to crop type, growth stage, and variety. It had to be easy to use and reliable under real farm conditions.

After many trials and adjustments, the team developed calibrations and agronomic models that supported accurate recommendations. The result was a tool farmers could carry in their pockets to guide one of the most important decisions in crop production: how much nitrogen to apply and when to apply it.

From early prototypes to a new generation

The first versions of the N-Tester were built in collaboration with external partners and used mainly by agronomists and larger farms. As digital tools evolved, so did the vision for the device.

Around 2015, YARD began building the next generation in-house with the goal of modernizing the tool, connecting it to smartphones, and opening it to many more farmers.

The result was the N-Tester BT, launched in 2019. The new device connected to smartphones and expanded access well beyond its early user base.

The experience evolved from relying on printed calibration sheets to a fully digital system that integrates multiple data points, delivering more accurate and timely guidance throughout the season.

“The focus remains on solving real-world problems for farmers, ensuring they have practical, evidence-based tools to help them apply nitrogen efficiently,” explains Mladen Miljic, Senior Manager for Farm and Field Hardware/IoT at Yara AgTech.

How it works

The device clips onto a leaf and measures its chlorophyll content. Since chlorophyll is directly linked to the plant’s nitrogen status, each reading gives an immediate picture of the crop’s needs. The device then converts the measurement into a nitrogen recommendation based on YARD’s calibrations.

Instead of relying on assumptions or one-size-fits-all formulas, farmers receive guidance that reflects the crop’s actual condition at that moment, allowing them to adjust their applications with more clarity and confidence.

Supporting farmers worldwide

“We have thousands of devices across Europe, including more than 5,000 in France alone,” says Michael Lepelley, Marketing and Agronomy Director at Yara France. “Farmers use it across the Nordics, Eastern Europe, the UK, Germany, and even Argentina. The N-Tester has helped farmers apply only what the crop actually needs, reduce overuse, and protect the environment. It has also contributed to yield increases of up to 120 kilograms per hectare and protein improvements of up to 0.2 percent.”

Interest continues to rise as more farmers connect with the idea of responding to the crop in real time.

In France, the N-Tester is seen as a reference tool, supported by both direct reach and a strong network of distributors and cooperatives. Together, these efforts have connected 500,000 hectares to N-Tester insights.

Digital tools are expanding this reach further. With Atfarm, farmers can use N-Tester measurements to create field-specific variable rate application maps. This links the moment a leaf is clipped to the moment fertilizer is applied in the field.

“It brings clarity to nitrogen management and helps farmers reach their yield and quality goals,” says Gustavo. “It delivers practical decisions backed by science and grounded in what the plant shows on that very day.”

Three decades on

The N-Tester has lived through major shifts in agriculture. It began as a modest idea in a research center and has become a trusted companion in fields across the world. Three decades later, it remains a simple tool with a powerful purpose, guiding farmers toward clarity, confidence, and better-informed decisions.