Glossary
VRA (Variable-Rate Application)
Applying inputs — seed or granular fertilizer — at rates that change across a field according to a prescription map, instead of one flat rate everywhere.
Definition
Variable-Rate Application matches the rate of an input to the local need of each management zone in a field. Instead of spreading 80 lb/ac of fertilizer across an entire quarter, a VRA job pushes more onto the productive zones and less onto the saline, eroded, or low-yielding ones. On a drone, the prescription map is loaded into the flight controller, GNSS positioning tells the aircraft which zone it is over, and the spread rate is adjusted on the fly. The result is the same airframe and the same pass, but a rate that updates continuously along the flight path to match the map — which is typically built on a 1–5 m zone resolution rather than a per-square-metre grid.
In an Alberta Context
Alberta fields are rarely uniform — a single quarter can carry black loam, a saline slough margin, and a gravelly knoll. A flat fertilizer rate over-feeds the weak ground and under-feeds the productive ground. A drone running VRA from an NDVI or yield-based prescription puts the product where it pays, which on variable east-central Alberta land is often the difference between break-even and a clear return on the spread. Note that drone VRA in Canada today is centered on granular spreading — fertilizer and seed. Variable-rate liquid pesticide application by drone is a separate matter, now moving under a narrow interim pathway following PMRA’s June 2026 Letter of No Objection, not blanket approval.
Why It Matters
VRA is where drone spreading earns its agronomic edge: it can place fertilizer more precisely than a flat-rate pass, putting product on the zones that pay and pulling it off the zones that cannot use it. Logistics cost versus a floater depends on field conditions and rates — the consistent win is placement, not a blanket cost claim. VRA also strengthens the OFCAF and 4R/sustainability documentation growers increasingly need, because applying less product on the zones that cannot use it is both an agronomic and an environmental win.
Frequently Asked Questions
+Can you variable-rate seed and fertilizer with a drone?
Yes. With a prescription map loaded, a spreader-equipped drone changes its granular rate by zone as it flies. Variable-rate granular fertilizer and seeding are the standard VRA jobs in Canada today. Variable-rate liquid pesticide application by drone is a separate matter, now under a narrow interim pathway following PMRA’s June 2026 Letter of No Objection.
+What map types work best for VRA in east-central Alberta?
A current-season drone NDVI flight is the most accessible starting layer, ideally combined with last year’s yield-monitor data and a soil test. NDVI alone shows vigour, not nutrient need, so ground-truthing with soil or yield data produces a more honest prescription.
+Do you need RTK for variable-rate drone spreading?
RTK or a comparable correction improves zone placement accuracy and is preferred for tight zones near saline margins or knolls. For broad zones a standard GNSS fix can be adequate; the right answer depends on how fine the prescription is.
+What file formats can you take a prescription map in?
Most prescriptions arrive as a shapefile; some controllers also accept GeoTIFF or GeoJSON. If you already have an Rx from your agronomist, send it over and we will confirm it loads cleanly before the job.