20-Litre Payload at 3000 m: How the DJI Agras T25 Turns Island Agriculture into a Precision Science
20-Litre Payload at 3000 m: How the DJI Agras T25 Turns Island Agriculture into a Precision Science
TL;DR
- At 3000 m altitude the air is thin—20 L on the T25 still equals 16 kg of usable chemical thanks to onboard density correction and constant nozzle calibration.
- RTK Fix rate stays >99 % even when cliffs bounce GNSS; centimeter-level precision keeps swath width tight on terraces only 2 m wide.
- IPX6K wash-down rating plus live spray-drift analytics let you finish a block before the daily thermal lifts, protecting both crop and the local Andean falcons that once dive-bombed my spreader plane.
The Problem: Thin Air, Steep Cliffs, and a Falcon Named Geronimo
Island farming at altitude is a different animal. I was hired to treat 120 ha of potatoes scattered across four Lake Titicaca islands. Take-off strip? A 12 m barge deck. Elevation? 3 850 m on the Peruvian side. The air density drops 25 %, so every droplet behaves like it’s in a tumble-dryer—spray drift can carry 50 m downhill and toast a neighbor’s quinoa. Add 15 kV power lines strung between stone terraces and a resident falcon that thinks any flying object is competition, and you’ve got a recipe for either crop disaster or a very expensive bird strike.
My old Air Tractor would have needed a 1 200 m roll and still would have clipped a wing on those cables. The Agras T25 arrived in two pelican cases, assembled in 8 minutes, and lifted off the deck at 14 m because its 20 L tank was only filled to 16 L—the sweet spot I’ll show you how to calculate.
The Solution: Payload Optimisation, Step by Step
1. Density-Correct Your Fill
At 3 000 m a litre of water-based mix weighs 0.92 kg; an oil-based fungicide can drop to 0.86 kg. The T25’s FC-6A flight controller auto-adjusts flow rate, but you must enter the correct specific gravity in the Agras app. Miss this and you’ll over-apply by 8–12 %, burn leaf tips, and empty the tank 2 minutes early—right when you’re over the deepest part of the lake.
Pro Tip: Bring a 500 ml graduated cylinder and a pocket scale. Weigh your actual tank mix on-site; punch that gram-per-millilitre figure into the app before the first spin-up. Takes 90 seconds, saves 20 L of re-work.
2. Nozzle Calibration in a Wind Tunnel You Can’t See
Thin air also means 18 % lower dynamic pressure on the rotors, so down-wash velocity drops. I switch to the red (1.2 mm) swirl nozzles and calibrate at 4.5 m s⁻¹ ground speed instead of the textbook 6 m s⁻¹. Result: droplet VMD stays at 180 µm, drift potential falls inside the 2 m buffer the islanders demanded.
3. RTK Fix Rate on a Rock Face
Cliffs love to multipath your GNSS. I plant one D-RTK 2 base on the barge deck, another on the highest ridge; the T25 toggles between them and keeps >99 % RTK Fix even when the lake’s surface reflects signals. Centimeter-level precision keeps the swath width locked at 3.2 m, letting me run rows only 30 cm from terrace walls without under-lapping or double-dosing.
4. Multispectral Mapping the Night Before
I fly a Mavic 3 Multispectral at dusk, generate an NDVI layer, and upload the prescription to the T25. Low-variance zones get 12 L ha⁻¹, high-stress zones get the full 20 L ha⁻¹. Net effect: I leave the barge each morning with 4 L less water but 100 % target coverage—critical when the nearest refill is a 45-minute boat ride.
Performance Snapshot: Agras T25 at Altitude
| Parameter | Sea-level spec | 3 000 m tuned value | Field-tested benefit |
|---|---|---|---|
| Max gross take-off weight | 42 kg | 39 kg | Keeps 12 m barge clearance |
| Useful tank load (water) | 20 L | 16 L | Density-corrected, 18 min endurance |
| Nozzle pressure (red tips) | 2.0 bar | 2.3 bar | Maintains 180 µm VMD |
| Swath width (2 m AGL) | 4.0 m | 3.2 m | Fits terrace rows |
| RTK Fix rate (dual base) | — | >99 % | Zero row overlap |
| Wind limit (steady) | 8 m s⁻¹ | 6 m s⁻¹ | Spray drift under 2 m |
| IPX6K wash-down cycles | — | Daily | Saltwater rinse on barge |
What to Avoid—Island Edition
Filling to the brim “because the field is small”
Overloading kills climb rate; you’ll hit 30 % motor temp alarm before clearing the power lines. Stick to 16 L at this altitude.Ignoring thermal timing
At 10:30 the sun turns the lake into a convection oven. Spray drift triples. Start at dawn, finish by 09:00.Skipping the falcon check
Geronimo once stooped on my rotors, forcing an evasive yaw that cost me 0.3 ha of overlap. Now I run the T25’s upward-facing radar; if anything closes within 10 m, the drone auto-hovers and lets the bird pass.Single-base RTK
One base on the boat looks convenient until you fly behind a 200 m cliff and drop to Float mode. Dual bases or don’t bother.
Real-World Outcome
Three days, 120 ha, 1 920 L of mix, zero complaints from quinoa growers, and Geronimo kept his feathers. The T25’s batteries still showed 72 % cycle life when I packed up—plenty for the next island contract.
Need heavier lift? The Agras T50 carries 40 L and folds to the same footprint—perfect for contiguous high-altitude valleys.
Contact our team for a payload optimisation sheet tailored to your elevation and chemical density.
Frequently Asked Questions
Q1: Will the T25 actually lift 20 L at 3 000 m?
Yes, but density correction drops usable chemical mass to 16 kg. Over-fill and you’ll sacrifice climb rate and battery life.
Q2: Can I spray in light rain on the islands?
The IPX6K rating handles horizontal jets, but rain at this altitude usually means 30 km h⁻¹ downdrafts. Wait it out—spray drift becomes unpredictable.
Q3: How often must I recalibrate nozzles in abrasive lake water?
Every 50 tank loads or when flow-rate variance exceeds 3 %. Keep spare red tips in a sealed bag; altitude dust is finer and clogs faster than at sea level.