C-DRONE GUIDE · 5 AUGUST 2026
Variable-rate nitrogen with a drone: prescription maps for wheat and rapeseed, method, prices
Nitrogen is a cereal grower's largest input bill — and the most sensitive one: too early or too much, and it is lost while lodging the crop; too late or too little, and it costs yield and protein. Yet no field is homogeneous: soil types, previous crops, wet spots and hilltops create requirements that can double within a hundred metres. Variable-rate application means mapping that variability — that is where the drone comes in — then driving the spreader with a prescription map instead of a flat rate. Long reserved for farms with on-board sensors, the method has become a per-field service. Here is how it works and what it costs.
Published on 5 August 2026, reviewed on 5 August 2026 — regulations in force as of August 2026.
What the drone measures: the crop's actual nitrogen status
The on-board multispectral sensor measures vegetation reflectance in bands invisible to the eye — near infrared and red edge in particular. From these bands come indices correlated with biomass and chlorophyll content, two excellent indicators of nitrogen nutrition status. On rapeseed, the classic application is the biomass assessment at the start and end of winter, which feeds directly into the planned-dose calculation: the drone replaces manual weighing with an exhaustive map of the field. On wheat, mapping mostly serves to adjust the final applications — the ones that build protein — by revealing deficient areas and already-saturated ones.
The approach is documented under real conditions: the study by Francesco Argento, Thomas Anken and their Agroscope colleagues, published in 2021 in Precision Agriculture, compared uniform and variable-rate fertilisation driven by a multispectral drone and soil data on winter wheat over several seasons: variable rate improved nitrogen use efficiency by around 10% at maintained yield (see the study on Google Scholar). Less nitrogen lost also means less volatilisation and leaching — the environmental argument meets the economics.
From flight to console: the prescription map
The typical service runs in four steps:
- Multispectral flight at the right stage (end of winter for rapeseed, stem elongation to flag leaf for wheat), on a programmed route — a hundred hectares is covered in a morning.
- Processing: index calculation, cleaning (clouds, shadows), zoning of the field into three to five homogeneous classes.
- Prescription: translating the classes into rates with the farmer or their adviser, within the total planned dose of the fertilisation plan — variable rate redistributes, it does not raise the regulatory ceiling set in nitrate-vulnerable zones.
- Export in a console-readable format (shapefile or ISOXML): the map loads into the spreader or sprayer terminal, which modulates on its own, GPS leading.
The drone is not the only possible sensor — satellites and on-board sensors exist — but it brings centimetre resolution, independence from cloud cover and day-precise scheduling, three decisive assets at growth stages where a few days matter. For row crops and vines, the same sensors serve other diagnostics — see our guide to water stress mapping by drone.
What variable rate pays back
The gain plays out on three fronts. Fertiliser first: on a heterogeneous field, redistributing the dose avoids over-fertilising areas already well supplied — at current ammonium nitrate prices, a few units saved per hectare pay for the mapping. Yield and quality next: deficient areas finally get their due, which evens out yield and above all wheat protein content, a payment criterion at the grain merchant. Agronomy last: less lodging in over-fertilised areas, less disease in overly dense canopies, and a solid file for certification schemes and supply-chain specifications.
Nitrogen mapping fits naturally alongside the other diagnostics of the same flight or season: emergence counting in spring, grassland biomass, hedgerow mapping for CAP subsidies — pooling campaigns cuts the cost of each. And for the application itself, the drone can take over where the spreader cannot go — see our guide to agricultural drone spraying and spreading.
2026 prices
Orders of magnitude observed in France in 2026 (excl. VAT):
- Multispectral mapping + prescription map: €8 to €20 per hectare depending on campaign size, tapering beyond a hundred grouped hectares.
- Minimum call-out package (travel, processing, console export): €300 to €500 — hence the value of grouping fields with neighbours, through the machinery ring or the cooperative.
- Season subscription (two to three flights at key stages, rapeseed + wheat): quoted case by case, typically €15 to €30/ha overall.
The return on investment depends on how heterogeneous the fields really are: on a uniform plain, variable rate adds little; on contrasting soils, it pays for itself in the first season. A test flight on a field known for its variability is the best starting point. This service draws on our drone agriculture offer: request a quote stating crops, areas and spreading equipment (console brand) for a directly compatible export.