Early days
In the early years of pasture development in New Zealand, a horse-drawn, wheeled spreader box was used. Fertiliser was poured in from bags, and released from the bottom of the box as it moved along.
Later spreaders consisted of a hopper filled with fertiliser, mounted on the back of a tractor. A spinner underneath threw the fertiliser sideways and backwards as the tractor moved along. As the spread was much greater than the width of the tractor, this was a more popular method than the box spreader. It is the main type of equipment used today.
Spreading by contractors
Particularly on large farms, contract firms are increasingly being used. With large trucks and hoppers, they can do a farmer’s job in a fraction of the time.
Spreading by farmers
Some farmers own large tractors and spreading equipment, and spread fertiliser as needed.
On dairy farms, cows spend only one day or night grazing each paddock before being moved to the next. Nitrogen fertiliser is often applied to each paddock after each grazing. This does not require a contractor, so is often done using the four-wheel-drive farm bike with a spreader attachment behind.
Types of spreaders
Spinning disc
This is the most common type of ground spreader. Fertiliser is dropped onto a spinning disc that has several radial vanes, from which the particles are flung horizontally. Disc diameters are usually about 750 millimetres, and typical speeds range from 750 to 1,000 revolutions per minute. Most designs have two discs rotating in opposite directions, with the fertiliser fed between.
Spinning disc spreaders are robust, and can handle a wide range of fertilisers and application rates. Swathe widths of 25–30 metres can be obtained, depending on the size of fertiliser particles. A 1-millimetre-diameter particle can be flung 3 metres from the disc, whereas a 5-millimetre-diameter particle would travel 15 metres.
Oscillating spout
This machine uses a spout that moves rapidly from side to side. The speed and length of the spout determines the spread pattern. Although more complex than a disc, it can achieve a very accurate spread, with swathe widths up to 15 metres.
Blower
This type of spreader is very simple, and is often used to place fertiliser in areas difficult to access. However, a uniform spread is hard to achieve. A mixture of particle sizes seems best, with an optimum diameter of 5–6 millimetres.
With all these spreaders the fertilised pattern and rate will be affected by the spreader design and speed, the fertiliser type, and the accuracy of the driver in spacing successive passes.