Kōrero: Topdressing

Whārangi 4. Origins of aerial topdressing

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The hard way

On hill country, the only way to get fertiliser and seed onto the land was to carry bags on horse back to the area, and then spread the material by hand. Contract labour was often used. It was extremely hard work, and stories abounded of farmers, having paid the contractors, finding bags of unspread fertiliser thrown into gullies.

In the 19th century and the first half of the 20th, there was no other way to do it. Any alternative was therefore eagerly anticipated.

Early proposals

Some pilots returning from the Second World War were keen to keep flying, and the aerial application of fertiliser seemed to offer possibilities.

The impetus for the use of aircraft came from advocates of aerial sowing onto bare areas to control erosion. The first aerial sowing on a New Zealand farm was in November 1947 at Ōmarama in North Otago. After initial reluctance, the Public Works Department, the Departments of Air, Scientific and Industrial Research, Agriculture, and the newly formed Soil Conservation and Rivers Control Council became involved in proposals for aerial topdressing of fertiliser. Doug Campbell, chief advisor on soil conservation to the Soil Conservation and Rivers Control Council, was one of the main advocates.

Taking off

John Lambert of Hunterville is often cited as the first to suggest using aircraft to spread fertiliser. He did this in a letter to his MP in 1926. But on 8 March 1941 Alan Prichard, at Ninety Mile Beach, was the first to actually sow seeds (of lupin) from the air, pouring them out the side window of a plane, a Miles-Whitney Straight. This gave the idea some credibility. All this was at a time when it was illegal to drop anything from an aircraft – even over your own farm.

Ōhakea trials

The first trials were at Ōhakea, near Palmerston North, in September 1948. The pilot flew a Grumman Avenger torpedo bomber aircraft from the New Zealand air force, testing fertiliser spread at aircraft altitudes ranging from 21 to 180 metres and a speed of about 200 kilometres per hour.

In fixed-wing aircraft the hopper is behind the pilot, its doors opening on the underside of the fuselage. They release the fertiliser, which falls into the slipstream of the aircraft. This creates turbulence, helping to spread the fertiliser laterally.

It was soon apparent that the type of superphosphate fertiliser had a large effect on the spreading result. The ideal form was granular, with as little fine material as possible.

Several flights at an altitude of 120 metres and a track spacing of 28 metres gave satisfactory results with superphosphate, at 2 hundredweight/acre (250 kilograms/hectare).

Hill-country trials

Trials followed on a typical hill-country farm near Raglan in the Waikato, also with the Grumman Avenger. The first results were poor because airframe vibration caused the superphosphate to compact in the hopper, and restricted the flow. Later trials with granular fertiliser showed a good spread at a rate of 250 kilograms per hectare.

Spreading lime

An attempt to spread lime was made in May 1949 using two Grumman Avenger aircraft. However, the planes had to return to their base because the lime would not flow at all. The problem was solved, at least temporarily, by putting a small amount of superphosphate into the hopper first, to start the flow.

By 1949 it was generally agreed that aerial topdressing had great possibilities, and that further development lay in the hands of commercial operators and not the air force.

Me pēnei te tohu i te whārangi:

John Maber, 'Topdressing - Origins of aerial topdressing', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/mi/topdressing/page-4 (accessed 24 June 2024)

He kōrero nā John Maber, i tāngia i te 24 Nov 2008