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 analyzing your crops with the N-Tester BT.

Please note before you start:

• Read here what's required to use the N-Tester.
• These crops are supported for the N-Tester Recommendations.
• Fertilize your field no more than one week after the N-Tester reading.

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.

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 a field from the field list.
   • Add a crop type and variety to your field to ensure N-Tester BT Recommendations are supported in your region. Find a list of supported crops here.
4. Scroll down to the N-Tester section on the field page.
5. Click Start N-Tester reading.

3) Adapt app permissions

As N-Tester Recommendations are not only crop specific, but also country and region specific, we need to know where your fields are located. For this we need accurate location access to your mobile device. For Android devices, we also need nearby devices access.

Adjust the Atfarm app permissions as follows:

Android

1. Click Allow in the location permission prompt in the app, then select Allow while using the app.
2. Go to the settings of 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.
7. Go back one step to the Permissions page.
8. Click Nearby devices.
9. Select Allow for nearby devices access.

iOS

1. Click Open Settings in the location permission prompt in the app.
2. Click Location in the permission settings.
3. Select Always for location access and switch on Exact location.

4) Connect the N-Tester BT

Connect your N-Tester BT as follows:

1. Click Connect N-Tester BT in the Atfarm mobile app.
2. Turn on Bluetooth® wireless technology on your mobile device.
3. Return to the Atfarm mobile app.
4. 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.
5. If the pairing was successful, you'll receive a signal from the app and the blue LED will stay on.
6. 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.

5) 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:

• The recommendation may not be accurate if there is a high amount of non-crop biomass or if the field has irrigated crops.
• 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.

• Ensure that the LED lens and light sensor in the head of the N-Tester BT are clean and dry. Any dirt, dust or scratches may result in inaccurate measurements. You can clean the entire N-Tester BT with a clean, damp cloth. Don't put it under running water or use chemical cleaners. When cleaning the lens, be gentle and only clean if you can see dirt or grime on it. Use a clean, soft, dry cloth to gently wipe the lens.

• Measure in mostly dry weather. A little drizzle or fog is fine, but avoid measuring in a downpour, both for your own good and for accuracy. Large water droplets can alter the measurements and give inaccurate readings. If there is a little dew on the leaves of your plants, you can brush off the drops before measuring and still get accurate results.
• An internet connection is required to download a satellite map of your field so that we can guide you to the appropriate biomass zones on your field. You can go offline again when taking the readings.
• 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. The Atfarm mobile app displays the battery level after the calibration step, so you can easily check it.
• Turn off silent mode on your phone as we use sounds to guide your readings.
• Keep your phone screen unlocked while taking the readings so they can be saved.
• Take 30 readings to get the recommendation: take 15 readings from the reference zone, and after this go to an average zone and take 15 other readings.

• Select a plant at the correct growth stage, such as BBCH 30 - 51.
• Measure at the center of the blade of the youngest fully developed leaf. Measurements on leaves that aren't fully developed may result in higher recommendations.
• 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. Click Start N-Tester measurements.
2. We're downloading the satellite map of your field so we can guide you to the appropriate biomass zones on your field.
   • An internet connection is required to download the map. You can go offline again when taking the readings.
3. You'll see a confirmation that the map has been downloaded.
4. Go to the middle of the reference zone (dark green).
   • The blue dot on the map shows your current position. If there isn’t a blue dot, click the location icon at the bottom right to locate your position.
5. Take 15 readings from the reference zone with the N-Tester BT.
   • 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.
   • Below the map you can see how many readings you've taken.
6. Click Move to average zone once you've completed the 15 readings in the reference zone.
7. Go to the middle of the average zone (light green).
   • The blue dot on the map shows your current position. If there isn’t a blue dot, click the location icon at the bottom right to locate your position.
8. Take 15 readings from the average zone with the N-Tester BT.
   • 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.
   • Below the map you can see how many readings you've taken.
9. Press and hold the On/Off button on the N-Tester BT for a few seconds to switch it off once you've taken all 30 readings.

6) Get the recommendation

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

1. Click Complete and see result in the Atfarm mobile app.
2. The nitrogen recommendation is displayed on your screen:
   • Yes: your crop needs nitrogen
   • No: your crop doesn't need nitrogen
   • The recommendation is saved under N-Tester Recommendations on the field page.
   • We're working to provide you with a quantitative nitrogen rate recommendation in lbs N/ac. In the meantime, please contact your Yara representative for more information.
3. View the relative N-Tester values in % for the reference zone and average zone below the recommendation.
4. Click Choose your next field to return to the field list and select your next field to measure with the N-Tester BT.

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