Spray drones used 96.7% less water than a tractor in a real field trial

What a real field trial found

A spray drone is a small aircraft that flies itself over a field on a set path and releases pesticide or fertilizer through nozzles slung underneath it. A tractor mounted boom sprayer is the older method, a tank of diluted chemical pulled behind a tractor, with a long arm of nozzles that sprays as the tractor drives across the field. Researchers in Lorestan province, Iran, ran both methods on the same wheat field, between April 10 and June 1, 2024, and measured exactly how much water each one used. The tractor sprayer used 300 litres of water a hectare. The drone used 10 litres. That is a reduction of 96.7%, calculated here from the 2 numbers the trial measured, because the drone applies a concentrated dose from close range instead of spreading a diluted tank across the whole field.

A widely repeated marketing figure claims drones cut water use by about 90%. That claim usually compares a drone against a person carrying a knapsack sprayer on their back, not against a tractor, a comparison a drone wins more easily. A separate real trial on steep vineyard terraces in China measured that exact comparison. A person spraying by hand used 504.72 litres of water a hectare. A drone flying 1 pass over the same vines used 123.12 litres, a reduction of 75.6%. A second pass, added to raise coverage, used 246.24 litres, still a reduction of 51.2%.

What actually powers a drone today

Flying a spray drone through a full working day is not solar powered today. The same Iran trial states plainly what it actually takes to keep 1 drone flying all day.

To ensure uninterrupted spraying operations using drones, it is essential to utilize a portable electricity generator along with three to four spare batteries per drone.

Mojtaba Safaeinejad, Mahmoud Ghasemi Nejad Raeini and Morteza Taki, a document quote, from the authors of the Iran field trial, in the discussion section of the paper. Source 1.

The same researchers name solar power only as something that could help later, not what happens now.

Using renewable energy sources, such as solar panels, to charge drone batteries could significantly reduce the environmental impact.

Mojtaba Safaeinejad, Mahmoud Ghasemi Nejad Raeini and Morteza Taki, a document quote, from the same authors, naming solar power as a suggested future improvement. Source 1.

A separate peer reviewed review priced what building a solar charging station for these drones would cost in India today, at 400,000 to 1,100,000 Indian rupees, and says the idea has not scaled past small pilot projects, because of the cost, the difficulty of storing enough power in batteries, and unpredictable weather.

Less carbon dioxide, and no wheel on the soil

The same Iran trial also measured what each method released into the air. The tractor produced 41.284 kilograms of carbon dioxide a hectare. The drone produced 14.485 kilograms, a reduction this article calculates at 64.9%.

A drone never puts a wheel on the ground, avoiding the soil compaction that a peer reviewed review says now affects about 68 million hectares of farmland worldwide and can cut a corn yield by as much as 50% under the worst measured conditions.