What is topdressing?
There are two main ways to apply fertiliser to pasture (for cattle and sheep) or crops.
- Aerial topdressing: small aircraft and helicopters fly back and forth across hilly farmland, dropping fertiliser as they go. This leaves a fine covering over a wide area.
- Groundspreading: trucks or tractors spread fertiliser as they move over flat or gently sloping land.
Why is fertiliser important in New Zealand?
The farmers who grow pasture and crops, and foresters who grow trees, want them to grow as fast as possible. To boost plant growth, they need to add fertiliser to the soil. The most common fertiliser in New Zealand is superphosphate.
Each year over 2 million tonnes of fertiliser are applied to pastures, crops and forests. Without it, the farming economy could not survive.
On the ground
Once, horses pulled a spreader box, from which fertiliser spilled out onto the soil as the horse moved along. Later, tractors used machinery to throw the fertiliser out over a much wider area. This method is still used. Some farmers use a 4-wheel farm bike with a spreader behind it.
From the air
In the 1940s, when farmers were eager to find an easier way to apply fertiliser, air force pilots who had returned from the Second World War were keen to keep flying. As a result, engineers, agricultural scientists, pilots and others worked out how small aircraft could drop fertiliser from the air.
The first test flight was in 1948. The pilot flew a torpedo bomber fitted with a hopper and doors in the floor, through which the fertiliser was released. After improvements, this method became a great success: it was much quicker and cheaper, and soon farms around the country were using it – especially in remote hill country. By 1958 there were 73 topdressing companies.
- The most common aircraft is the Fletcher, designed by an American.
- In 2007, 33 companies used planes and 88 used helicopters, which spread fertiliser from a large bucket hung below.
- About 750,000 tonnes of fertiliser are dropped each year.
- A spreader under the hopper throws the fertiliser over a wide area.
- Sometimes planes crash. But safety awareness has improved, and fewer pilots have been killed in recent years.