Once you've added your fields, you can create Variable N-Rate Application maps both in the Atfarm mobile app on your mobile device, as explained in this article, and in the Atfarm web app in your desktop browser.

In the Atfarm mobile app, the application maps are auto-generated using the VRA N-Sensor algorithm. If you create the application map in the Atfarm web app, you can also choose to draw the application map from scratch using the brush editor and define fertilisation zones and amounts yourself.

Tip: You can create application maps for multiple fields of the same crop type at once in the Atfarm web app. Read here how to proceed.

Please note before you start:

• Read here about the equipment required, file types by terminal and how to request a test file.
• The maximum field size for creating application maps is 1,500 ha. The minimum field size is 1 ha with a minimum field width and length of 50 m. Read here about the field sizes.
• To create an accurate application map, ensure that non-crop areas are excluded when adding your fields to Atfarm. When you draw the field, you can add inner boundaries and adjust the outer field boundary.
• We don't currently take fertiliser restrictions into account when creating application maps. When fertilising your crops, please remember to adjust the fertiliser application to comply with government fertiliser restrictions.
• Grassland: You can create application maps for mown grass (not grazed grass) consisting mainly of ryegrass (Lolium sp.), fescue (Festuca sp.) and timothy (Phleum sp.) with no more than 5 % clover in the sward. However, we're already working on calibrating the algorithm for grass with higher clover content.

1) Select your field

Initiate the map creation as follows:

1. Log in to the Atfarm mobile app on your mobile device.
2. Select the desired farm in the farm overview.
3. Select the desired field in the field overview.
4. Click Add application map.

2) Select biomass

You're now in the VRA Map Builder.

Proceed as follows:

1. Select the biomass map date from below the map.
   • The application maps are created from biomass indexed satellite imagery.
   • Only cloud-free satellite image dates are listed, as biomass indices can only be applied to cloud-free images. However, sometimes dates are marked as cloudy in the timeline when they're actually cloud-free. Read here how to view cloudy satellite images.
   • For best results, use the most recent image as it will reflect the current crop status. The image should be no more than five days old, as older images may show biomass values that don't reflect current conditions. When using old images, make sure they reflect the current crop performance.
2. Click Continue to basic settings to proceed to the next step.

3) Add basic settings

You'll now enter information to be considered in the application map calculation.

Proceed as follows:

1. Select the fertiliser you want to apply from the first dropdown.
   • The fertilisers that can be selected depend on your country. If you don't see your fertiliser in the list, select Other or Generic.
2. If necessary, adjust the % N in the fertiliser in the next input field.
   • The % N content expresses the nitrogen content in 100 kg of fertiliser.
3. Enter the target N rate in kg N/ha in the next input field. 
   • The target N rate is the average nitrogen rate to be applied to the field. It's the main input to the VRA N-Sensor algorithm. The satellite images provide information about the different nitrogen uptake in the field, but they don't provide actual absolute nitrogen values. You can use the Yara N-Tester to determine the agronomically optimal nitrogen rate for your next application.
4. Enter lower and upper limit in kg N/ha in the next input fields.
   • The lower and upper limits define the minimum and maximum application rates for the applied variable rate strategy. If the field areas with their calculated application rates are outside these limits, the application rates are adjusted to the set limits. If the calculated application rates are within the limits, the limits aren't applied.
   • For the levelling strategy, the lower limit applies to areas with high biomass/N-uptake and to areas with exceptionally low biomass/N uptake (<30 % of average field N-uptake).
   • For protein dressing, the lower limit applies to areas of low biomass/N-uptake.
   • The recommended lower limit is 1 kg N/ha. The upper limit should be at least +/- 10 kg N/ha from the target N-rate.
5. Depending on the crop type, select the growth stage of your crop for the biomass map date from the dropdown.
   
   • The VRA N-Sensor algorithm is based on thousands of samples and lab tests and adapts to the crop and growth stage.
   • We recommend a growth stage based on your crop type. As variable rate fertilisation isn't recommended for each growth stage, these can't be selected.
6. Click Continue to spreading strategy to proceed to the next step.

4) Select strategy

You'll now configure settings for the application:

1. Depending on the crop type and growth stage, click on Levelling or Protein dressing to select the variable rate strategy.
   
   • The levelling strategy applies higher nitrogen rates to areas with lower biomass/nitrogen uptake and lower nitrogen rates to areas with higher biomass/nitrogen uptake.
   • The protein dressing strategy applies higher nitrogen rates to areas with higher biomass/nitrogen uptake and lower nitrogen rates to areas with lower biomass/nitrogen uptake.
   • If you don't see this option, Atfarm has automatically selected the strategy. Read more about the strategies here.
2. Click on Zone Map or Raster Map to select the rate adjustment strategy.
   • Zone map: Neighbouring pixels with similar N-uptake and corresponding nitrogen levels are grouped into zones. The gradations are created in 10 % steps. This makes it easier to use spreaders which have +/- 10 % buttons. The zone map is best used for manual applications or older terminals. When using the Atfarm mobile app as a terminal and selecting to spread by speed, the zone map is coarser and is therefore recommended as less manual control of the spreader is required.
   • Raster map: The N-uptake and application rate are calculated per pixel and the fertiliser is applied accordingly. The raster map is designed for maximum precision on high-end equipment.
3. Click Generate application map to generate the application map.
   • The application map is saved under your field, so you can also continue with it later.
4. You can now view the application map created with the application zones.
   • The application map consists of a biomass map with the fertilisation pixels as squares or dots depending on the rate adjustment strategy selected. Each colour represents a different nitrogen rate in kg/ha.
   • You can see average N in kg/ha, total N in kg, total fertiliser and the cell size.
   • Each pixel on the map represents the centre of a 20 x 20 m cell. This design allows you to see the biomass through the pixels. The 20 x 20 m pixel resolution is sufficient for current spreader models (most over 20 m spreading width) and can also be used for spreaders with a larger spreading width.
   • Each corner of the field must have a nitrogen value associated with it, even if most of the 20 x 20 m cell is outside the field, so that your terminal can read the application map. You just have to work on the field boundaries as usual. Pixels with areas outside the field boundary are handled by Atfarm's boundary handling algorithm and the application rate is calculated only for the areas of the pixels within the field boundary.
   • The cell size refers to the spatial resolution of the pixels from the satellite data. The scaling of the cells depends on the size of the field. The larger the field, the larger the scale (20 x 20 m, 40 x 40 m, 60 x 60 m, 80 x 80 m, etc.). The larger the scale, the lower the spatial resolution of the pixels from the satellite data.
   • You can adjust the fertilisation zones and amounts in the Atfarm web app.
5. Click View application map to proceed.

5) Create application task

You'll now see the application map with different coloured pixels. The pixels represent the application zones with different amounts of fertiliser in kg/ha to be applied to achieve the target N-rate. A colour scale below the map shows the amounts per colour.

Create the application task as follows:

1. Click Create application task to create the application task.
2. You can see the task outline with details: fertiliser to be applied, total fertiliser, mid flow rate in kg/ha.
3. Select the driving mode with the green switch. We use your GPS location to determine the application rate, so you can manually adjust the driving speed or flow rate as you drive.
   • Spread by speed
     • If it's not possible to adjust the spreader's flow rate while driving, use this mode to adjust the driving speed. The app detects which application zone the tractor is in and it's current speed and displays the speed to drive at to achieve the desired result.
     • Using tractors with a low number of gears, or where changing gears requires the clutch to be pressed, can result in uneven driving and unwanted spreading. Therefore, the tractor should have several gears in the speed range. To avoid a drop in speed when changing gears, it's recommended to use a tractor with a power shift or CVT or IVT transmission.
   • Spread by flow rate
     • If the spreader terminal has a manual control system and can adjust the flow rate while driving, use this mode to adjust the fertiliser application by means of the spread rate. The app will then indicate how much to manually increase or decrease the spread rate on the spreader terminal based on the application map.
4. Spread by speed only: Enter your preferred mid speed under Calibrate mid speed. The driving speed range will be adjusted accordingly.
5. Click Start driving.
6. Activate location tracking on your mobile device, so the application rate can be adjusted based on your current position in the field.
   • Set the GPS accuracy of your mobile device to a high level.
   • The GPS accuracy may be limited in forested areas and deep valleys.

6) Start the application

You'll see a map showing your current position on the field. Prepare your equipment and begin your variable application as follows:

1. Mount your mobile device in the tractor cabin.
2. Adjust the spreader settings for the mode you've chosen:
   • Spread by speed: Set your spreader to the mid flow rate and tractor to the mid speed shown on the screen.
   • Spread by flow rate: Set your spreader to the mid flow rate shown on the screen.
3. Start driving and follow the instructions shown in the app.
   • Spread by speed: Maintain the driving speed shown in the app.
   • Spread by flow rate: Follow the flow rate shown in the app.
4. To stop the application and continue at a later time, simply go back in the app or close the app. The application task is saved under the field or in the Tasks tab.
   
   1. Click View application tasks in the tasks section.
   2. Click on the task in the list of tasks to open it.
   3. Click Start driving to continue with the task.
5. To complete the application task, click Mark as completed in the app.
6. Click Confirm job complete to complete the task.
   • Click Continue driving to continue with the application task.
   • The completed application task with details of the driver, date, area and time can be found under the field or in the Tasks tab.