Once you've added your field, you'll see a satellite map of the field with a biomass layer overlaid. Read here about the different satellite maps.

You can choose from three types of biomass maps to view variability within the field. Click on the map layer tile in the bottom right corner of the field map and choose between

• Normalized Difference Vegetation Index (NDVI) map

• Optimized map

• N-uptake map

Normalized Difference Vegetation Index (NDVI) map

The Normalized Difference Vegetation Index (NDVI) map uses the Normalized Difference Vegetation Index (NDVI) to show the nitrogen deficiency on targeted vegetation. This map allows you to quantify the difference between healthy and stressed vegetation.

The Normalized Difference Vegetation Index (NDVI) measures the reflection of red and near-infrared light by vegetation. It then calculates a relative value between zero and one, which indicates the presence or absence of green biomass. Biomass levels are represented using a fixed green color scale. Dark green areas represent higher biomass/nitrogen availability, while light green areas represent lower biomass/nitrogen availability.

However, this index has a limit. As the shoot develops (canopy saturation, highest biomass), the index saturates very quickly and differences between highest and lowest growth can no longer be detected. Please use the Normalized Difference Vegetation Index (NDVI) map only in early growth stages to plan your first application. For later applications, use the optimized map or the N-uptake map.

Optimized map (N-Sensor map)

The optimized map is based on the Yara N-Sensor Index, which makes Atfarm's biomass maps unique. The index has been developed based on Yara's expertise in precision fertilization and more than 25 years of field trials with the Yara N-Sensor. Read more about it here.

The Yara N-Sensor Index measures not only red and near-infrared radiation as the Normalized Difference Vegetation Index (NDVI), but also the spectral ranges in between. With this fine gradation and the inclusion of crop and regional data, the N-uptake can be determined even for advanced growth stages. With the optimized map you can not only analyse crops and identify differences in N-uptake throughout the growth cycle, but also across seasons.

The color scale is a relative scale with no absolute values. The colors are adjusted based on the lowest and highest index values in a satellite image. Low biomass/nitrogen uptake is represented by brown tones. A variety of greens represent canopy evolution. As the canopy evolves, the color changes to blue and purple shades.

The Yara N-Sensor Index is insensitive to different growth stages and canopy saturation. It doesn't tend to saturate as quickly as the Normalized Difference Vegetation Index (NDVI) and correlates better with nitrogen uptake. Depending on the crop, the index starts to saturate at around BBCH 50-60.

Use the optimized map to plan your second, third and protein dressings and create Variable N-Rate Application maps.

N-uptake map

The N-uptake map has been developed and validated using data from field trials and passive measurements with the Yara N-Sensor.

The N-uptake map shows the daily absolute field average N-uptake in kg N/ha. The above-ground N-uptake is calculated for each pixel from the latest cloud-free satellite images. The map shows the total amount of nitrogen absorbed by the crops up to the time the image was taken. This makes the N-uptake map ideal for identifying variations in N-uptake within a field.

The legend uses a color scale from yellow to dark green and shows a dynamic scale. Yellow represents the lowest kg N/ha, which is -30 of the daily average, while dark green represents the highest amount of kg N/ha, which is +30 of the daily average. The map therefore shows a total variance of 60 kg N/ha within a field.

Use the N-uptake map to plan your second, third and protein dressings and create Variable N-Rate Application maps.

The N-uptake map is currently available for several crops, with the N-uptake layer being accurate for specified growth stages and less accurate for unspecified growth stages: