background image
Forage & Nutrition
Guide 2018
The physical characteristics of the fertiliser will affect how
evenly it spreads and the settings required. The key factors are:
Density of the fertiliser: low-density fertiliser, such as urea
(80 per cent normal density), is more difficult to throw.
Size of the granules: generally larger particles will throw
further. Particle-size distributions, with the majority of
particles (80 per cent) in the 2-4mm range, will usually
allow a good spread to be achieved, but larger diameters
(3-4.5mm) will probably make it easier to achieve wider
spread widths. The component parts of blends should have
similar-size distributions.
Shape of the granule: rounded particles will roll off the disc
more predictably than irregular granules.
Strength of granule: strong particles will resist break-up on
the disc.
Remember, when purchasing fertiliser, always take physical
quality into account when making choices.
Urea will be more widely used across all farm types in the future.
Its lower density presents a greater spreading challenge and
it usually will not spread as wide as denser material. Look for a
urea product with larger particle sizes by asking the supplier for
the size distribution figures. Even with a good-size distribution,
it is vital that the correct spreader setting is used and that the
limitations of the spreader with urea are observed (maximum
bout width, etc.). Wind will affect urea more than ordinary
fertiliser so spread in calm conditions if possible. Blends of
urea and conventional density fertiliser need to be considered
very carefully as they can be difficult to spread without the
components segregating across the bout width.
Spreaders need to be correctly set/adjusted for specific
fertilisers at specific bout widths. Some spreader models require
very careful setting. The components that are adjustable vary
between manufacturer and model but include one or more of
the following:
Disc type;
Power take off (PTO)/disc speed;
Vane type and position/angle on disc;
Position of fertiliser drop point;
Disc height over crop/soil; and
Spreader/disc angle.
The setting is determined by fertiliser type (density, particle
size distribution, shape, strength) and bout width. Setting
information is usually available in detailed setting charts
provided by the manufacturer, but increasingly is more easily
accessible on the internet or as a smart phone app. While some
manufacturers provide setting information for specific fertiliser
brands, increasingly a simple sieve test and visual type test are
used to identify fertiliser type and consequently the settings
required. It's vital to follow the setting procedure.
Getting the correct rate of fertiliser out (kg/ha or bags/acre) is
also important and while manufacturers' setting guides are a
starting point, some level of field calibration is usually needed.
Some makers have very useful setting aids and of course on-
board weighing systems make it very easy. Whatever system is
used, it is important to establish the correct rate setting before
field-scale errors are made
Correct attachment to the tractor to make sure it's level from
right to left and at the correct angle front/back and height
over the crop is essential, as is a working rev counter. Driving
at accurate bout widths is essential; tramlines facilitate this
in cereals and GPS guidance systems can help when there are
no tramlines. However, there is no shame in measuring and
marking the bouts! Wear on the spreader components, such as
the fertiliser outlet, disc, vanes or spouts, must be monitored.
To avoid uneven spreading on the headland and the loss of
fertiliser into headlands/drains, most spreaders have a headland
setting mechanism which adjusts the spread pattern. Matching
the in-field runs with the headland runs requires the spreader to
be turned on and off at exactly the correct times as the tractor
approaches and leaves the headland on high-tech spreaders,
this can be automatically controlled by GPS, but careful manual
operation is possible once the distances are known.
0 5 10 14 19 24 29 34 38
Lateral distance (m)
Application rat
e (%)
Figure 2: Basic (shaded area) and overlapped (line) spread pattern at 18m shouldered pattern.