How can I connect the N-Tester BT to the Atfarm app and measure with it?

Once you've installed the Atfarm mobile app on your mobile device and added your farms and fields to your Atfarm account, you can start analysing your crops with the N-Tester BT.


Please note before you start:


  • Read here what's required to use the N-Tester.
  • We don't currently take fertiliser restrictions into account for the N-Tester Recommendations. When fertilising your crops, please remember to take into account the maximum nitrogen requirement according to government fertiliser restrictions.
  • The N-Tester can't indicate future soil nitrogen supplies, such as from applied nitrogen that plants haven't yet absorbed due to drought. Please use your experience to evaluate the nitrogen recommendation.



Follow these steps to connect and measure with the N-Tester BT:



1) Install the app


If you haven't already done so, download the free Atfarm mobile app for iOS and Android smartphones and tablets from the common app stores. Simply scan the QR code below with your smartphone or tablet camera and follow the link to download and install the Atfarm mobile app. Alternatively, search for 'Atfarm' in the app store.


Install from Google Play Store:


Install from Apple App Store:




2) Prepare the analysis in the app


Begin the analysis in the Atfarm mobile app as follows:


  1. Log in to the Atfarm mobile app on your mobile device.
  2. Add or select your farm.
  3. Add or select your field.
  4. Scroll down to the N-Tester section on the field page.
  5. Click Start N-Tester reading.
  6. Appears only the first time: Select the N-Tester BT from the list of N-Tester models.
    • You can manage your N-Tester models in the settings.
  7. Select the variety from the first dropdown.
    • Differences between varieties are considered in the calculation using correction factors.
    • Find an overview of the supported N-Tester varieties here.
  8. Select the growth stage of your crop.
    • Find an overview of the supported crops and growth stages here.
  9. Enter the grain yield expectation for this year in t/ha in the first input field.
  10. Select the Soil Nitrogen Supply (SNS) from the next dropdown.
  11. Enter nitrogen already applied since planting/seeding in kg N/ha in the next input field.
  12. Select if this is the last dressing.
  13. Click Start measuring.
  14. Read the tips displayed in the app for successful measurement.
  15. Click Start measurements.
  16. Enable accurate location access. As N-Tester Recommendations are not only crop specific, but also country and region specific, we need to know where your fields are located.
    • Android
      1. Click Allow on the location permission prompt, then select Allow while using the app.
      2. Go to the settings on your mobile device.
      3. Go to Apps, then select Atfarm from the apps list.
      4. Click Permissions, then select Location.
      5. Select Allow all the time for location access.
      6. Switch on Use precise location.
    • iOS:
      1. Click Open Settings on the location permission prompt.
      2. Click Location in the permission settings.
      3. Select Always for location access and switch on Exact location.
  17. Return to the Atfarm mobile app.



3) Connect the N-Tester BT


Connect your N-Tester BT as follows:


  1. Turn on Bluetooth® wireless technology on your mobile device.
  2. Press and hold the On/Off button on the N-Tester BT for a few seconds to switch it on.
    • The LED flashes blue after initialization and indicates the pairing process.
    • A red flashing LED during initialization indicates that the batteries need to be replaced.
    • The app automatically establishes a temporary connection in the background. The Bluetooth® wireless connection isn't activated by connecting the device in the Bluetooth® wireless technology settings of the operating system (Android, iOS), as is usually the case with other devices.
    • On some mobile devices a window with Bluetooth® wireless connection options will appear, don't connect the N-Tester BT in this window.
  3. If the pairing was successful, you'll receive a signal from the app and the blue LED will stay on.
  4. Click Continue in the app.
  5. The app guides you to take an empty reading against ambient light to calibrate the device. Press and hold the N-Tester BT head closed for a few seconds until your mobile device vibrates.
  6. You'll now see a biomass map of your field and an N-Tester reading counter at the bottom.
    • The map date is shown below the map.
    • Change the map layer using the dropdown below the map.



4) Measure your crops


Once you've successfully connected your N-Tester BT to the Atfarm mobile app, you're ready to measure your plants.


Before you begin, please note the following for accurate results:


  • Make sure the field has enough sulfur. A sulfur deficiency, like a nitrogen deficiency, will make the leaves lighter and the nitrogen recommendation may not be correct. Other nutrients have no significant effect.
  • Make sure that your mobile device and the N-Tester BT have enough battery power so that the device doesn't switch off during the measurements. If this happens, you'll have to restart the whole measurement process.
  • Turn off silent mode on your phone as we use sounds to guide your readings.
  • Your mobile device can remain in your pocket during the measurement.
  • To obtain a representative average reading, measurements must be taken randomly across the field on at least 30 representative plants.
  • For best results, move through the field in a W pattern.




  • Select a plant at the correct growth stage (BBCH 30-51) and measure at the centre of the blade of the youngest fully developed leaf. Measurements on less developed leaves may lead to higher recommendations.
  • Avoid atypical field areas, such as areas with distinctly different soil properties, such as sand banks or similar.
  • Avoid grained or thick leaf tips, leaves with visible drought stress, or rolled leaves.





You're now ready to measure your plants:


Tip: The following steps can be performed with the test disk to practice or check your N-Tester BT. Place the test disk in the measuring head so that the green glass covers the lens.




  1. Take a reading of your plant.

    • Place the leaf inside the measuring head using the center line as a reference. The lens must be completely covered. The leaf adjuster can be moved to fit the width of the leaf. If the leaf is incorrectly positioned on the measuring head or if the leaf is too dirty or wet, an error message will appear.
    • Press the measuring head together using the thumb rest and hold until the LED flashes. You'll also receive a notification on your mobile device. An unsuccessful measurement is indicated by either a red LED light or a notification from the app. In this case, please repeat the measurement.
    • The reading counter in the app shows you how many readings you've taken.
  2. Go to the next plant and take another reading. Measure at least 30 plants in total.
  3. Press and hold the On/Off button on the N-Tester BT for a few seconds to switch it off once you've finished taking readings.





5) Get the recommendation


Once you've completed the readings, proceed as follows to get the recommendation:


  1. Click Get the N-Tester value in the app.
  2. The nitrogen recommendation in kg N/ha for your crop is displayed on your screen.
    • The recommendation is saved under N-Tester Recommendations on the field page.
    • Click Show more insights to see the average N-Tester value and the inputs you entered for the measurement.
    • Click Show N-Tester values to see the N-Tester value for each reading. These values are an intermediate result obtained by the N-Tester.
    • Click Repeat measurement to repeat the readings.
    • Click the 3 dots in the top right corner and select Delete measurement to delete the measurement.



Use the N-Tester Recommendation to create Variable N-Rate Application (VRA) Maps in Atfarm. To do this, enter the recommendation in kg/ha as your target N-rate.



The Bluetooth® word mark and logos are registered trademarks owned by Bluetooth SIG, Inc. and any use of such marks by Yara International ASA is under license. Other trademarks and trade names are those of their respective owners.

Was this article helpful?

24 out of 32 found this helpful

Have more questions? Submit a request



Please sign in to leave a comment.