Photo credit: STRATUS
The practice of Variable Rate Fertilizer Application (VRFA) based on historical average yield maps allows farmers to optimize fertilizer use by targeting specific zones within their fields. This practice relies on precision machinery equipped with yield monitors and GPS systems that collect data during harvest. These systems record the productivity of different zones within the field, generating detailed yield maps as the starting point for VRFA.
The practice begins with gathering historical yield data using harvesters equipped with yield monitors. These monitors measure crop productivity across the field, while GPS systems log the spatial coordinates, ensuring that each yield measurement is tied to a specific location. Farmers then upload this data to Geographic Information System (GIS) platforms such as QGIS or ArcGIS, or they can use commercial digital platforms designed to simplify the process by automatically generating maps.
The next step is to process and analyze the yield data. Farmers, agronomists, or advisors use GIS tools to create variable rate application maps, which divide the field into zones based on productivity. Highproductivity zones may require less nitrogen, while lower-yielding zones may need more nutrients to enhance growth. The practice, however, does not inherently incorporate soil characteristics or climate conditions, which can significantly affect yield data. Farmers should complement the maps with soil tests or past climate information to avoid misinterpretation. For example, a low-yielding area might result from poor soil fertility, waterlogging, or drought rather than a nutrient deficiency. Integrating soil sample results or climate records ensures more reliable and actionable fertilizer recommendations. Once the VRFA maps are created, farmers can edit or adjust them based on their field knowledge and observations. Most GIS or commercial platforms allow modifications to the map, ensuring it aligns with reality. For example, if a farmer knows a zone had low productivity due to a pest outbreak or extreme weather, they can reduce the fertilizer dose for that area to avoid overapplication.
The final step is implementation. The VRFA map is exported as a file compatible with the farm’s variable rate fertilizer spreader or precision equipment. When uploaded to the equipment’s onboard terminal, the machine adjusts the fertilizer application rates in real time, based on the instructions in the map. This process ensures precise nutrient delivery, increasing efficiency, and minimizing environmental losses.
While VRFA does not necessarily reduce the total amount of nitrogen fertilizer used, it optimizes distribution, improving nutrient efficiency and reducing potential fertilizer runoff or leaching. This results in environmental benefits, compliance with regulations, and potentially improved yields. By incorporating soil and climate data, alongside historical yield maps, the method becomes even more robust, supporting long-term sustainability and profitability for farmers.