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.
Origins
Previous aerial applications 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.
Early efforts 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 DaniellJust turned 25 he purchased his remote Wairarapa hill-country farm in the winter of 1913. Wearing a harness supporting a hand-operated seed distributor and towing packhorses, he began re-seeding his farm. Enlisting in 1915, he watched from the trenches in France and ached for the day the bomber aircraft might instead spread seed and fertilizer on Wairere. When it became known Henry Ford had invested in the heavy cargo-carrying aircraft industry, he at once wrote to Ford pointing out this potential but never received an acknowledgment from Ford. To the irritation of the new leaders of the new aerial-topdressing industry, Len always remained an advocate of so much less accident-prone large aircraft, in particular Bristol Freighters. He believed real cargo aircraft to be properly powered and designed and built for the job. Furthermore, the industry as it developed with small aircraft required substantial farmer investment in infrastructure unnecessary for the big planes. Accordingly, he declined persistent offers of directorships of their companies, instead long maintaining hopeful watch on SAFE. 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.
Alan Prichard 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 . On Monday 10 March, they sowed , 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.
Prichard wrote up the experiment in the NZ Journal of Agriculture (vol 70 p117-120). This came to the attention of the Minister Bob Semple, who Prichard occasionally flew as a VIP. Semple asked how Prichard had obtained permission. Prichard admitted he had not, and had "cribbed" back the time in the ZK-AFH's logbooks by extending the time of other flights. Semple encouraged Prichard to continue, adding "Don't let anyone catch you, and if they do, send them to me". After the outbreak of World War II, he had the good fortune to retain the use of ZK-AFH, when most aircraft were impressed for war service. Prichard conducted various trials between 1939 and 1943, from an early stage adding fertiliser to the seeds, which was found to dramatically improve growth. The success of the fertiliser was such that his trials came to concentrate on this aspect, and its possible application to existing pasture.
As a result of Prichard's experiments, in 1945 the Department of Agriculture estimated aerial topdressing would cost about £4 per ton of fertiliser (on a basis of 2 cwt per acre), which was economic (actually, this price turned out to be a significant overestimate). Prichard now found an ally who could officially sanction further trials.
Doug Campbell Doug Campbell was an agricultural academic concerned about soil erosion. He had been suggesting the spread of both seed and fertiliser for erosion control and aerial spreading of trace minerals since the 1930s, but had not conducted trials until he met Prichard. Campbell brought official backing and academic responsibility to Prichard's work. Immediately after the war, he obtained permission to build a sheet metal hopper for ZK-AFH to test the spread of bluestone crystals. In 1946 the first pure topdressing flight was conducted without seed. Mixtures of bluestone crystals, sulphate of ammonia, slaked lime and carbon black were used. The lack of a lid for the hopper initially resulted in irritating dust spreading through the aircraft in turbulence: in cold wet conditions it was necessary to heat the hopper to prevent the fertiliser coagulating, while in dry conditions the powder tended to disperse in the wind before reaching the ground. Nevertheless, in July Campbell arranged for ZK-AFH to topdress 1,100 acres (4.5 km2) of a copper-deficient farm. In August 1947 trials with cobalt sulphate in liquid form were conducted on the farm of K. M. Hickson near Taumarunui, with a horseback-mounted radio used to convey results to the pilot. It was soon suggested that cobaltised superphosphate would be easier to spread, although it was felt a specialised aircraft would be needed to do this.
Campbell published his research in the New Zealand Journal of Science and Technology, Volume X, 1948 as "Some observations on top dressing in New Zealand".
Convinced by the trials, Campbell formed the co-ordinating and advisory committee on aerial topdressing with representatives from the Ministry of Public Works, Department of Agriculture, Department of Air, DSIR and the Soil Conservation Council. At the committee's first meeting on 27 November 1947 it resolved to ask the Royal New Zealand Air Force for assistance.
RNZAF trials Between the second world war and the cold war, the RNZAF was a large and competent organisation without a lot of work to do. It responded enthusiastically to Campbell's suggestion, initially proposing to use Tiger Moth and DC-3 aircraft, but concerns about corrosion lead them to use "expendable" war surplus Grumman Avengers.
Experiments were resumed on 5 September 1948 using a Miles Whitney Straight and three Grumman Avengers; the RNZAF put superphosphate in a converted long range fuel tank in Avenger NZ2504 and dropped it over the concrete runway at Ohakea. (NZ2504 is now preserved in the Royal New Zealand Air Force Museum).
The superphosphate was too powdery but a more granular form was found before final trials measuring distribution pattern of spread by air on 16 September 1948. The results were considered very promising. Trials proceeded to hill country at Te Mata near Raglan, and were extended to three other sites.
For 1949 a Research and Development flight was formed under Stan Quill, equipped with the three Avengers and a Douglas DC-3, while instructions were sent to England to modify 2 RNZAF Miles Aerovans then on the production line to carry one-ton hoppers. A ground convoy of station wagon, car, one-ton truck, jeep, fuel tanker and radio van supported them. The 1948 fuel tank was replaced by a hopper with sides angled at 60° with a vibrating rod to loosen the superphosphate. Large-scale topdressing started on 14 March 1949 spreading clover-super mix. The "Topdress III" trials culminated on 21 May 1949 with a demonstration drop on 11 different properties close to Masterton in front of large numbers of farmers and press. These trials were calculated to have spread 2.5 cwt/acre (31,000 kg/km2) at an all-up cost of 15 shillings ($1.50) per acre (4047 m2), despite the use of inappropriately over-powered combat aircraft. Further public displays were given to cabinet ministers on 30 August at Johnsonville, on 9 September at Ohakea and at a 17 September Air Force Day air show. As these trials were a resounding success, in addition to the Aerovans, 12 Bristol Freighters then under construction for the RNZAF were modified to take superphosphate hoppers.
Following these successful trials, in 1950, farmers' groups lobbied the government to have the RNZAF provide subsidised topdressing with the Bristol freighters and even advocated using large Handley Page Hastings. But by this time government work was being overtaken by private enterprise as ex-airforce pilots bought New Zealand-built De Havilland Tiger Moth biplanes cheaply, placed a hopper in the front seat and went into business flying from the paddocks of any farmer willing to pay. The government became reluctant to spend money on interfering with the increasing number of commercial operators.
Research in other nations
Australia The first experimental topdressing in Australia was done by a private Tiger Moth in 1948.
Great Britain