Aerial Topdressing - Origins - Alan Pritchard

Alan Pritchard

The idea of spreading seed also occurred to Alan Pritchard, 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 Pritchard 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 Pritchard was holding back men needed to sow lupin seed. Remembering the grape seeds, Pritchard suggested sowing the seed by air. Burying the hatchet, Harrison and Pritchard 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, Pritchard 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.

Pritchard 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 Pritchard occasionally flew as a VIP. Semple asked how Pritchard had obtained permission. Pritchard 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 Pritchard 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. Pritchard 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 Pritchard'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). Pritchard now found an ally who could officially sanction further trials.

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Alan Pritchard

Alan Pritchard was a pilot for the New Zealand Public Works Department from the late 1930s to mid-1950s. Using a Miles Whitney Straight from 1939 on his own initiative and sometimes forging aircraft log books to conceal his work, Pritchard conducted trials of aerial seed sowing and spreading fertilizer which ultimately lead to the development of aerial topdressing.

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