You have read "15 to 25 percent overlap loss" in every catalog. But how many litres, and how much money, is that on your fields? This article gives the formula and works it through on a 120-hectare farm step by step. Pen and paper are enough.
Where overlap happens
With manual section control chemical is applied twice in three places:
- Headland turns: as the boom enters and leaves the edge strip the operator closes a section late or opens it early. Each turn double-sprays an area of boom width × delay distance.
- Pass-to-pass overlap: on parallel passes the driver cannot hold the track exactly; 30 to 80 cm of overlap remains between passes. This silent loss covers the whole field.
- Wedge-shaped parcels: on non-rectangular fields the last passes narrow; part of the boom falls on sprayed ground or the neighbour's parcel.
Guidance removes item two; automatic section control removes items one and three.
The formula
We calculate the three items separately and add them. The data you need:
- A: field area (ha)
- B: boom width (m)
- L: average pass length (m)
- g: overlap per pass (m), typically 0.5 m when driving without GPS
- d: delay distance at the turn (m), typically 3 m with manual switching
- k: wedge/irregularity share, 2 percent on rectangular fields, 6 to 10 percent on irregular ones
1. Pass overlap (ha): number of passes ≈ (A × 10,000) / (B × L). Each pass double-sprays g × L m².
Loss₁ = passes × g × L / 10,000 = A × g / B
2. Turn overlap (ha): at both ends of each pass B × d m² is double-sprayed.
Loss₂ = passes × 2 × B × d / 10,000 = A × 2d / L
3. Wedge share (ha): Loss₃ = A × k
Total overlap rate = (Loss₁ + Loss₂ + Loss₃) / A
A 120-hectare example
A wheat and sunflower rotation, 24 m boom, parcels averaging 400 m long, half of the fields irregular.
- A = 120 ha, B = 24 m, L = 400 m, g = 0.5 m, d = 3 m, k = 5 percent
Loss₁ = 120 × 0.5 / 24 = 2.5 ha
Loss₂ = 120 × 6 / 400 = 1.8 ha
Loss₃ = 120 × 0.05 = 6.0 ha
Total = 10.3 ha, so 8.6 percent of the seasonal application area is sprayed twice. That may look modest, but with three applications per season (herbicide, fungicide, insecticide) it is 31 hectares of chemical wasted.
At a chemical cost of 40 € per hectare: 31 × 40 = 1,240 € per year, before counting phytotoxicity on double-sprayed strips and the extra diesel.
On farms with many irregular parcels, k = 10 percent and g = 0.8 m push the same calculation to 14 percent, which is where the catalog figures come from.
Which technology removes which item?
| Item | Guidance only (Nova 2N) | Guidance + auto section (Nova 200) |
|---|---|---|
| Pass overlap | g 0.5 → 0.15 m: down 70% | same |
| Turn overlap | unchanged | d 3 → 0.3 m: down 90% |
| Wedge share | unchanged | sections close at the boundary: down 85% |
For the example farm:
- With Nova 2N the loss drops from 10.3 to 8.5 ha (about 220 € a year)
- With Nova 200 the loss drops from 10.3 to 1.8 ha (about 1,020 € a year)
So automatic section control pays for itself within a few seasons on this farm, faster on booms wider than 24 m and on more irregular land, and much faster where chemical costs per hectare are higher than in this conservative example.
How to find your own numbers
- Boom width and pass length: from the machine and the field register.
- Overlap (g): measure the gap between wheel tracks of two passes with a tape; 0.4 to 0.8 m is normal without GPS.
- Delay (d): mark where you close the section at the headland and where the edge strip actually ends; the distance between them.
- Nozzle output and target rate: hitting the right rate is the precondition for any loss calculation; check it with the Nozzle Calculator.
- Recorded covered area: Nova computers show the real covered area when a job ends. The difference to the registered field area is your true overlap rate. TIM APP reports that difference for every job.
We explained how automatic section control works in this article. Whether it can be fitted to your sprayer is covered in the GPS retrofit guide.
