Aerial topdressing is the aerial application of fertilisers over farmland using agricultural aircraft. It was developed in New Zealand in the 1940s and rapidly adopted elsewhere in the 1950s.

The first known aerial application of agricultural materials was by John Chaytor, who spread seed over a swamped valley floor in Wairoa, New Zealand, in 1906 using a hot air balloon with mobile tethers.

The first known use of a heavier-than-air machine in aerial application was on 3 August 1921 when, as a result of advocacy by Dr Coad, a USAAC Curtiss JN4 Jenny piloted by John A. Macready was used to spread lead arsenate to kill catalpa sphinx caterpillars near Troy, Ohio, United States. The first commercial operations were attempted in the US in 1924 and use of insecticide and fungicide for crop dusting slowly spread in the Americas and, to a lesser extent, other nations. Crop dusting poisons enjoyed a boom in the US and Europe after World War II until the environmental impact of widespread use was recognised following the publication of Rachel Carson's Silent Spring in 1963. Crop dusting was not adopted in New Zealand until after top dressing was well established.

Initial interest in New Zealand concentrated on seed sowing, but much of New Zealand's central North Island farmland, given to returned servicemen after World War I, had proven deficient in trace minerals such as cobalt, copper and selenium, forcing difficult topdressing by hand in rough country, or abandoning the land for forestry. The possibility of using aircraft was soon investigated.

Spreading superphosphate by agricultural aircraft was independently suggested in 1926 by two New Zealanders, John Lambert of Hunterville and Len Daniell of Wairere. There was some publicity when in 1936 Hawkes Bay farmer Harold McHardy used a de Havilland Gypsy Moth to sow clover seed on his own land. This led the Soil Conservation and Rivers Control Council to decide to fund aerial sowing and topdressing trials in 1937 to prevent erosion, but little progress was made, despite strong advocacy by Doug Campbell.

At that time it was illegal to drop anything from an aircraft, which dissuaded several advocates who felt a law change was needed before experiments could begin.

The idea of spreading seed also occurred to Alan Prichard, a pilot for the New Zealand Public Works Department, as he was flying E. Madden of the Ministry of Works in a de Havilland Moth, sharing grapes and throwing the seeds out of the open cockpits. A few months later Prichard was tasked with conducting an aerial survey in Northland. The survey was delayed when the Ministry's Miles Whitney Straight, ZK-AFH, was grounded by bad weather.

A supervisor, J. L. Harrison, complained that Prichard was holding back men needed to sow lupin seed. Remembering the grape seeds, Prichard suggested sowing the seed by air. Burying the hatchet, Harrison and Prichard spent that evening experimenting with methods of dispersal, before settling on sewing a sack onto a piece of downpipe. The following morning, 8 March 1939, Prichard flew over Ninety Mile Beach while Harrison, on his signal, held the downpipe out a window and emptied the sack. They then landed and examined the spread of the seeds. It was found a distribution of 1 seed per square foot was obtained from a height of 100 to 150 feet (46 m). On Monday 10 March, they sowed 375 acres (1.52 km²), using 2 lb/acre (224 kg/km²) instead of the 5 lb/acre (560 kg/km²) used when sowing by hand. The pair returned to examine the site at 2 weeks, 1 month and 2 years and at all points the aerially sown land was indistinguishable from that sown by hand.