Once you've added your fields, you can create Variable N-Rate Application (VRA) 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. However, you can only export application maps to your terminal from the Atfarm web app. So once you've created the application map, go to the Atfarm web app to export it.

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 fertilization zones and amounts yourself. However, you can also adjust the fertilization zones and amounts in the application maps created in the Atfarm mobile app when you prepare the export in the Atfarm web app.

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 5.79 ac. The minimum field size is 2.47 ac with a minimum field width and length of 164 ft. 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 fertilizer restrictions into account when creating application maps. When fertilizing your crops, please remember to adjust the fertilizer application to comply with government fertilizer 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 fertilizer you want to apply from the first dropdown.
   • The fertilizers that can be selected depend on your country. If you don't see your fertilizer in the list, select Other or Generic.
2. If necessary, adjust the % N in the fertilizer in the next input field.
   • The % N content expresses the nitrogen content in 100 lb of fertilizer.
3. Enter the target N rate in lb N/ac 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 lb N/ac 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 2.2 lb N/ac. The upper limit should be at least +/- 22 lb N/ac 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 fertilization 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: Neighboring 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 fertilizer 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 fertilization pixels as squares or dots depending on the rate adjustment strategy selected. Each color represents a different nitrogen rate in lb/ac.
   • You can see average N in lb/ac, total N in lb, total fertilizer and the cell size.
   • Each pixel on the map represents the center of a 66 x 66 ft cell. This design allows you to see the biomass through the pixels. The 66 x 66 ft pixel resolution is sufficient for current spreader models (most over 66 ft 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 66 x 66 ft 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 (66 x 66 ft, 131 x 131 ft, 197 x 197 ft, 262 x 262 ft etc.). The larger the scale, the lower the spatial resolution of the pixels from the satellite data.
   • You can adjust the fertilization zones and amounts later in the Atfarm web app when preparing to export the application map.
5. Click View application map to proceed.

5) Export map to your terminal

You'll now see the application map with different colored pixels. The pixels represent the application zones with different amounts of fertilizer in lb/ac to be applied to achieve the target N-rate. A color scale on the map shows the amounts per color.

Export the application map as follows:

1. Log in to Atfarm from your desktop browser.
2. Select the desired farm in the farm overview.
3. Select the field which you created the application map for in the field overview.
4. Click on the created application map under Recommendations to open it.
5. If necessary, click on Zone Map or Raster Map to adjust the rate adjustment strategy.
6. Optionally, use the brush editor to change the fertilization zones and amounts.
   • Click on the number below a color and enter the desired nitrogen rate.
   • Click on a color to select it, then click on a fertilization zone on the map to apply the new rate.
   • Use the + and - buttons on the map or your mouse wheel to zoom in and out.
   • Click Undo to undo your last change.
   • Click Reset to clear all changes.
   • To disable the brush, click on the selected color again.
7. Click Export to continue to the export.
8. You'll now see the application map with different colored pixels.
   • The pixels represent the application zones with different amounts of fertilizer in lb/ac to be applied to achieve the target N-rate. A color scale on the map shows the amounts per color.
9. If necessary, click Edit next to the fertilizer name to change rate adjustment strategy and fertilization zones and amounts. When finished, click Export to recalculate the application map.
10. Click the download icon next to the desired terminal export option.
    • The file type (ISO-XML, Shapefile) you need to download depends on your terminal. Read here about the equipment required, file types by terminal and how to request a test file.
    • If desired, select the PDF option to also save the application map as a PDF file. This is ideal for sharing and printing.
11. Click Download in the pop-up.
12. Save the file to the desired location on your computer.
    • Don't rename the folder or the files in the folder. Otherwise, the terminal may not be able to recognize them.
13. Extract the downloaded ZIP folder.
    • Most terminals require unzipped files. A few terminals require zipped files, for example Valtra. In this case, please skip this step.
    • Windows: Right-click the ZIP folder and select Extract All, then click Browse to select the location where you want to extract the folder, and then click Extract.
    • Mac: Double-click the ZIP folder. The newly extracted folder will appear in the same folder.
14. Store the extracted files from the unzipped folder on an empty USB drive.

    • Don't put any files other than the application files on the USB drive. Otherwise, the terminal won't be able to distinguish between the files.

    • You can store application files in Shapefile format for several fields on one USB drive and upload them to your terminal.
    • Don't store application files in ISO-XML format for several fields on one USB drive. Otherwise, the terminal won't be able to distinguish between the files. However, you can store the files on the same USB drive and transfer them one at a time, so that you only need one USB drive. To do this, empty the USB drive before each transfer.
15. Connect the USB drive to your terminal.
16. Load the files from the USB drive.
    • Please refer to your terminal's user manual for instructions on loading the application files onto the terminal.
    • For assistance, please contact your technician, local dealer, manufacturer, or contact our support team. Please let us know what terminal and spreader you're using and provide us with the files you're trying to upload.
17. The zones of the application map will appear on the terminal screen and the application rate will be set.