The role of the fertiliser spreader is often under-estimated in the even, accurate delivery of fertilisers (N, P and K).
Fertilisers are a significant cost in grassland and tillage farming systems, representing 20-30pc of total production costs for either a cereal or grass silage crop.
There are many steps involved in determining the actual rate of fertiliser, from soil sampling to preparing a fertiliser plan.
To profit from fertiliser planning it is essential that fertilisers are applied precisely and accurately.
There are a number of factors to consider before spreading fertiliser:
Choosing a spreader
The most important thing when choosing a fertiliser spreader is its ability to spread the types of fertiliser to be used at the desired bout widths, evenly.
This is determined by the spread pattern of the machine, which is assessed by a full tray test where every 0.25m or 0.5m width of the spread pattern is measured.
The fertiliser from each 0.25m or 0.5m wide tray is weighed and the evenness is assessed by the shape of the plotted graph and the calculated coefficient of variation (Cv%).
The physical characteristics of the fertiliser will affect how evenly it spreads and the settings required. The key factors are:
Fertiliser density: low-density fertiliser such as urea (80pc normal density) is more difficult to throw.
Granule size: generally larger particles will throw further. Particle size distributions with the majority of particles (80pc) 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 ideally have similar size distributions
Granule shape: rounded particles will roll off the disc more predictably than irregular granules or angular particles.
Granule strength/hardness: strong particles will resist break-up on the disc.
Setting the fertiliser spreader
There are two elements to getting fertiliser spread evenly at the correct rate in the field:
Setting the spreader to spread evenly with a particular fertiliser at a specific bout width.
Calibrating the spreader to spread the correct rate of fertiliser.
Setting for even spreading
Most modern spreaders need some level of setting or adjustment to enable them to spread different fertilisers at different bout widths. The elements that may be set depending on the machine design include:
* Disc type and speed.
* Vane type and position.
* Fertiliser drop point on the disc.
* Height above crop.
Spreader angle, eg tilting discs upwards at back to throw further.
The setting needed is machine specific and is based on the type of fertiliser being spread and the bout width chosen.
Basic information is given in the instruction manual, but increasingly either spreader manufacturer websites or phone apps are used to allow the operator to access up-to-date setting information.
The evenness of fertiliser spreading (spread pattern) can be assessed by collecting spread material (fertiliser) in a series of trays laid out across the bout width.
For a complete spread analysis, a full set of 0.25m or 0.5m-wide trays laid out across the bout width for a total width of between two and three times the expected bout width is required.
Level ground and wind-free conditions are also essential.
Following spreading over the trays, fertiliser is collected and weighed and from this single pass, the overlapped pattern can be generated and Cv%s calculated. This level of testing is rarely carried out in the field.
A faster but less accurate tray test is to place one tray every two metres between the bouts and to measure the overlapped pattern by pouring the fertiliser from the trays into a number of small cylinders which reflect the spread pattern.
Calibration of fertiliser spreaders is essential for accurate application rate of fertiliser, which is affected by:
* Bout width.
* Forward speed.
* Regulator setting.
Select a fertiliser spreader capable of even spreading at the desired bout width with the fertiliser types to be used.
Check spread pattern and Cv% values from independent or manufacturers tests.
Select fertiliser that has good spreading characteristics with at least 80pc of the granules in the 2-4 mm size range and preferably smooth round shapes.
To ensure an even spread across the bout width, set the spreader as accurately as possible for the fertiliser being used.
To apply the correct rate of fertiliser, the spreader should be calibrated, using the manufacturer's resources as a starting point.
Clean after every working day and protect from corrosion. Check all the spreading components for wear frequently.