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

This guide shows you how to use the N-Tester BT in the YaraPlus mobile app to measure your crop's nitrogen status and get a nitrogen recommendation.

The N-Tester BT measures leaf chlorophyll directly in the field. It's especially useful at later growth stages, when canopy-based methods like photo analysis are no longer suitable for the crop stage.

Before you start

• Fertiliser restrictions
  • The N-Tester recommendation doesn't take official fertiliser limits into account. Please make sure your fertiliser application complies with local regulations.

• Supported crops and timing
  • The N-Tester can only be used for supported crops, growth stages and varieties.
  • For supported crops and growth stages, see supported crops.
  • For supported varieties, see supported varieties.
  • Use the recommendation promptly and fertilise your field within one week after the measurement.

• Technical requirements
  • You'll need the YaraPlus mobile app and the N-Tester BT. If you don't have an N-Tester BT yet, see how to get one.
  • You'll need a stable internet connection to prepare a new measurement and load the recommendation. An internet connection isn't required while measuring with the N-Tester.
  • You'll need to allow location and Bluetooth® access. On Android 12+, you'll also need to allow Nearby devices.
  • Make sure your mobile device and the N-Tester BT have enough battery. The app shows the N-Tester BT battery level after pairing. How to change batteries

• Crop and measurement conditions
  • Make sure the crop is healthy and well supplied with all essential nutrients except nitrogen. Nitrogen should be the main limiting factor.
  • Sulphur deficiency can affect the result and lead to misleading measurements. Other nutrients typically have no significant effect on the measurement.
  • Measure in mostly dry weather. Light drizzle or fog is fine, but avoid measuring in heavy rain.
  • Large water droplets can alter readings. If there's dew, gently brush off the droplets before measuring.
  • Time of day, pesticide use, including strobilurins, and yield level don't influence the readings.

• Device care
  • Make sure the LED lens and light sensor in the measuring head are clean and dry. Dirt, dust or scratches may cause inaccurate measurements.
  • Clean the device with a clean, damp cloth. Don't put it under running water or use chemical cleaners.
  • For the lens, use a clean, soft, dry cloth and wipe gently only if needed.

• Method limitations
  • The N-Tester recommendation reflects the crop conditions at the time of measurement. It doesn't account for future soil nitrogen supply, for example nitrogen applied but not yet absorbed due to drought.
  • Please use your experience to evaluate the recommendation before applying fertiliser.

Quick start (7 steps)

1. Open YaraPlus > Activity > New activity > N-Tester measurement
2. Select your crop, production goal and variety, then choose N-Tester BT
3. Turn on the N-Tester BT and let the app pair automatically
4. Run calibration using an empty measurement
5. Measure at least 30 representative plants across the field
6. Tap Finish measurements, enter the required crop data, then tap View recommendation
7. Tap Save and exit and, if needed, assign the result to a field

Video guide

Watch this video and follow the steps below to learn how to use the N-Tester BT.

Step-by-step

Follow the steps below to perform an N-Tester BT measurement.

1. Allow permissions (one time setup)
2. Start measurement
3. Pair and calibrate the N-Tester BT
4. Measure plants
5. Enter crop data
6. View and save the recommendation
7. (Optional) Assign result to a field

1) Allow permissions (one time setup)

YaraPlus needs location access to place measurements on the map. The N-Tester BT connects via Bluetooth®, so Bluetooth® access is also required. On Android 12+, you also need to allow Nearby devices.

On iOS devices:

1. Go to your mobile device Settings.
2. Location: Go to Location services and enable the Location services switch. In the same screen, scroll down to YaraPlus and select it. Choose While using the app and enable Precise location.
3. Bluetooth®: In your device settings, go to Bluetooth® and enable the Bluetooth® switch. Then search for YaraPlus in your device settings and select the app. In the screen that opens, enable the Bluetooth® switch.

On Android devices:

1. Go to your mobile device Settings.
2. Location: Go to Location and enable the Location switch. Then search for YaraPlus in your device settings and select the app. Tap Permissions > Location > Allow only while using the app, then enable Precise location if available.
3. (Android 12+ only) Nearby devices: Go back to the permissions overview, select Nearby devices, then tap Allow.
4. Bluetooth®: In your device settings, go to Connections and switch Bluetooth® on.

Note: If you turn off any of these services after measuring, you'll need to enable them again before taking new measurements.

2) Start measurement

1. Log in to the YaraPlus mobile app.
2. Tap Activity in the bottom bar.
3. Tap New activity, then select N-Tester measurement.
4. Allow location, Bluetooth® and, on Android 12+, Nearby devices access if prompted.
   • If the dropdowns aren't loading, make sure location services are enabled in your mobile device settings, not only inside the app. Then restart the activity.
5. Select the crop you want to measure.
6. Select the production goal.
7. Select the variety.
   • Differences between varieties are considered using correction factors.
   • If your variety isn't on the list, select Unknown. You can still use the N-Tester, but results may be less accurate as there is no calibration for this variety. Please send us the variety name and we'll review it for future calibration updates.
8. Tap Continue.
9. Select N-Tester BT from the models, then tap Continue.
   • If you're using an earlier device model, use the instructions in this article.

Tip: You can also prepare measurements in the web app under Atfarm > Tools > Plan measurement. There, you can select multiple fields of the same crop type and variety with the same crop data inputs, and then create measurement tasks for them all at once, saving you time. Then open the mobile app, go to Activity > N-Tester, and select the prepared measurements to complete them in the field.

3) Pair and calibrate the N-Tester BT

1. If you haven't already, turn off silent mode on your mobile device. The app uses sounds to guide your measurements.
2. When prompted by the app, press and hold the ON/OFF button on the N-Tester BT for a few seconds to turn it on.
   • A blue flashing LED after initialisation means pairing is in progress.
   • A red flashing LED during start-up means the batteries need replacing. How to change batteries
3. Let the app connect automatically via Bluetooth®.
   • Pairing happens inside the YaraPlus app. If your phone shows a Bluetooth® pop-up, don't connect the N-Tester BT there. Close the pop-up and return to YaraPlus.
4. If pairing is successful, you'll get a signal from the app and the blue LED on the N-Tester BT will stay on.
5. Tap Start calibration.
6. Complete the empty measurement to calibrate the device. Press and hold the N-Tester BT head closed for a few seconds until your mobile device vibrates.
7. When calibration is complete, tap Start measurements.

You'll see the measurement screen with a satellite map of your field and a measurement counter below the map. Each measurement is geolocated on the map with a pin icon.

4) Measure plants

For reliable results, measure across the field to capture crop variability.

1. Walk a W-shaped path across the field and measure at least 30 representative plants.
2. Avoid atypical field areas, for example areas with distinctly different soil properties, such as sand banks.
3. Measure the youngest fully developed leaf.
   • Select a plant at the correct growth stage.
   • Avoid grainy or thick leaf tips, leaves with visible drought stress, or rolled leaves.
   • Measurements on less developed leaves may lead to higher recommendations.
4. Place the centre of the leaf blade inside the measuring head. The lens must be completely covered.
   • Use the centre line as a reference and adjust the leaf guide to fit the leaf width.
5. Press the measuring head together and hold it until the green LED flashes. You'll also get a signal on your mobile device and the counter increases.
6. If the measurement fails, you'll see a red LED and get a signal from the app. Reposition the leaf, wipe off moisture if needed, and repeat the measurement.
7. Repeat until you've taken 30 or more measurements.
   • The counter shows how many measurements you've taken.
   • Tap See all to view values, or tap a pin to view its N-Tester value.
   • To remove a value, tap See all, then tap the bin icon next to the value.
8. When finished, press and hold ON/OFF on the N-Tester BT for a few seconds to switch it off.

Measuring route

Leaf position

Tip: You can use the test disk to practise or check the N-Tester BT. Place the test disk in the measuring head so the green glass covers the lens.

5) Enter crop data

After measuring, enter crop information so the app can calculate the recommended N-rate.

1. Tap Finish measurements.
2. If you need to pause, tap Save and continue later. You can find saved measurements under Activity > N-Tester.
3. Select the farm from the first dropdown.
   • Make sure the farm is located in the same country as set in your account.
4. Select the growth stage.
5. Enter your yield expectation for this year.
6. Enter nitrogen applied at sowing.
7. Enter N-min.
8. Select whether this is the last dressing.
9. Select the N-Tester BT result you want to use for the recommendation.
   • The N-Tester value has no unit and is the median of your readings. It reflects your crop's nitrogen uptake. Read more about the N-Tester value
   • You can also add your own value by selecting Enter custom value.
   • Note: Using a custom value instead of your measurements may lead to inaccurate results.

6) View and save the recommendation

1. Tap View recommendation.
2. Review the nitrogen recommendation.
   • Based on your measurements and crop inputs, this is the suggested amount of nitrogen to apply during the current growth stage.
   • Fertilise your field within one week after measuring.
3. Tap See all data entered to review:
   • Crop data – inputs used for the recommendation
   • Single measurements – values behind the result
     • These values are intermediate results obtained by the N-Tester. Read more about the N-Tester value
     • Tap a value to show its location on the map.
4. If needed, tap the bin icon in the top right to delete the recommendation.
5. Tap Save and exit.

Completed N-Tester measurements are saved under Activity > N-Tester in the YaraPlus mobile app and under Atfarm > Tools > Activities > N-Tester measurements in the web app.

(Optional) Assign result to a field

1. Open the result and tap Assign field.
2. Select the farm.
3. Select your field from the list (or Add field).
4. Tap Next to confirm.

Troubleshooting

If you're stuck, start with the quick fixes below. For more issues, see How can I fix problems with the N-Tester BT or app?

• Permissions denied: enable the required location, Bluetooth® and, on Android 12+, Nearby devices permission in your mobile device settings, then restart the measurement.
• Phone shows Bluetooth® pairing options or asks for a PIN: don't pair in your phone's Bluetooth® settings. Close the pop-up and return to YaraPlus. Pairing happens inside the app. Full steps
• Blue LED keeps flashing and the app keeps searching: keep the app open and retry pairing. Toggle Bluetooth® off and on on your phone if needed. Full steps
• Calibration fails: make sure the measuring head is fully closed for a few seconds and the lens is clean and dry. If needed, switch the N-Tester BT off and on and restart the activity. Full steps
• Many failed measurements: make sure the leaf fully covers the lens, measure the centre of the youngest fully developed leaf, and avoid wet, dirty, rolled or stressed leaves. Wipe off moisture and try again. Full steps
• Saved measurement missing: go to Activity > N-Tester in the YaraPlus mobile app. Your saved N-Tester measurements are listed there. Full steps

What's next?

Use the recommended N-rate to:

• Create variable-rate application maps
• Plan fertilisation for the season
• Browse the Yara fertiliser catalogue

Learn more

What is the N-Tester value?

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.