What is Variable Rate Application (VRA)?

The progress of technology is also reflected in agriculture. Precision fertilization is made possible by using Variable Rate Application (VRA). With the VRA technology the application rate is precisely adjusted to a location or to the characteristics of an area. This saves materials and costs and better protects our environment.



What type of VRA does Atfarm provide? How does it work?


After adding your field to Atfarm, you can see a recent satellite image with a biomass layer on it. With this biomass map, you can create and individually adapt Variable N-Rate Application (VRA) maps to apply nitrogen variably. Our Variable N-Rate Application feature can be accessed both via the Atfarm web app in your desktop browser and via the Atfarm mobile app on your mobile device.




You can choose between 3 types of biomass maps. Each biomass map applies a specific vegetation index to a cloud-free satellite image to measure crop health and growth. As a result, you get a biomass map showing the in-field variability, which can be used to create Variable N-Rate Application (VRA) Maps.


Our Yara N-Sensor vegetation index is what makes Atfarm special. It was developed based on our expertise in precision fertilization and over 25 years of field trials. Using our Yara N-Sensor index, Atfarm generates optimized biomass maps to show the variability in crop development even in advanced growth stages. This is particularly relevant for late nitrogen applications.


Nearly all other offered tools use the Normalized Difference Vegetation Index (NDVI) based on red and near-infrared radiation – a technology older than 50 years – and can therefore only detect differences in early growth stages. From shoot development of the plants, this index saturates very rapidly and loses its informative value.


So far, only our Yara N-Sensor index can make biomass differences visible during and after shooting and create precise application maps for these growth stages.


You can export the generated Variable N-Rate Application (VRA) Map to your terminal or – if you do not have a Variable Rate Application (VRA) spreader – send it to your smartphone and simply use our free Atfarm mobile app as your terminal.


Benefits of Variable N-Rate Application (VRA) with Atfarm:



Increased nitrogen use efficiency


Less nitrogen remains in the soil after the harvest, leading to reduced risk of leaching


Lower nitrogen balance surplus


Easier compensate growth differences within a field


Reduced risk of crop lodging


Easier harvest due to more homogeneous crop growth


Higher yields and protein content depending on weather conditions



Which VRA strategies can I select in Atfarm?


After Atfarms algorithm calculated the nitrogen uptake of the canopy, two strategies can be selected:





The Levelling strategy addresses higher nitrogen rates to areas with lower biomass/nitrogen uptake and lower nitrogen rates for areas with higher biomass/nitrogen uptake. This is best used when nitrogen is the growth limiting factor and you want to ensure, that all areas in your field contain enough nitrogen.  This strategy is best used when the crop can still compensate growth differences usually during tillering, stem elongation and booting.





The Boosting strategy addresses higher nitrogen rates to areas with higher biomass/nitrogen uptake and lower nitrogen rates for areas with lower biomass/nitrogen uptake. This is best used when other factors (e. g. water availability) limit your crop growth and yield potential. The Biomass Cut-Off instructs the redistribution algorithm to cut back to the minimum application rate when the biomass measurement falls below a certain level. This ensures nitrogen is not wasted on areas of the field which are not likely to yield due to crop damage, water logging etc. Rather than applying very high rates of nitrogen due to the low biomass values it is assumed that the crop is uneconomical to treat and therefore cuts right back.


It's also recommended to use the Boosting strategy for protein dressings to assure consistent protein concentrations and to prevent protein dilution in high yielding areas. The protein dressing is intended for the last dressing at later growth stages. For cereals, this usually means from GS 60 in flowering, but can also be selected from GS 37 – flag leaf visible onward.


When creating a VRA map for your field, you can choose the Boosting algorithm only for late growth stages. If you want to choose the Boosting method for earlier growth stages, you can create the VRA map manually and then choose the Boosting method.

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