Applying fertilisers accurately and evenly is very important in order to maximise the benefits from their use to improve crop yield and quality as well as profitability.
Fertiliser spreader calibration
Why should I calibrate my fertiliser spreader?
Uneven spreading or spreading into field margins can cause a range of potentially serious problems including:
- Uneven crop growth
- Lodging (from over application) and disease
- Reduced yields and poor / uneven crop quality at harvest
- More risk of transferring nutrients to watercourses at field margins causing pollution.
- More risk of causing botanical changes in hedgerows and field margins
Spreading fertiliser and organic manures as uniformly and accurately as possible is a requirement in NVZs
Not spreading on hedgerows and ditches is a requirement of cross compliance
How do I maintain my spreader?
Fertiliser spreaders and sprayers should be regularly maintained and serviced replacing worn out parts as necessary.
- Wash out after use, don’t leave fertiliser in spreaders overnight it will cake and clog and accelerate corrosion
- Check bout width and rate settings (damp conditions will affect flow rate and spread pattern)
- Check for wear and functioning of discs, vanes, agitation, spouts and spreader plates and feed roller condition on pneumatic machines. Replace any worn parts.
- Check spinner speed using a tachometer, or check tractor PTO shaft speed at recommended engine revs.
How do I calibrate my fertiliser spinner?
There are two different types of calibration:
Rate calibration – that guarantees the correct amount and not an even rate of application over the field
Spread pattern calibration – which ensures an even rate over the field and should be done with each new type of fertiliser that is used in the spreader.
- Check that it is supplied with the machine and is easy to use
- Ensure that the lowest rates the machine can apply are appropriate to the bout widths to be used
- At wider bout widths there may be a limit to the rate that can be applied evenly
- The best way to do this is to use a tray test
- Ideally this should be done annually
- This will ensure that the spread pattern will remain the same even when different application rates of the same product are used.
- A spreader that is set to apply correct application rates will not necessarily spread the fertiliser evenly and in the right place. Tray tests show where the fertiliser is thrown from the machine.
- A full set of calibrated trays should be used to give the lapped spread pattern leaving gaps between trays can give misleading results.
Best practice spreading guidelines
Set the working height taking account crop height, as well as remembering to allow for wheel depressions under a load and the depth of the tramline.
Check the machine is level from side to side and set to a front to rear shape as specified by manufacturer for the material and bout widths being used
Check recommended PTO speed selected at the tractor actually matches the PTO speed at the shaft. If systems are hydraulically driven, check disc speed.
Forward speed selection on gravity fed spinners
The forward speed selected should allow the rate of flow of fertiliser from the hopper to be maintained regardless of the terrain.
Calibrating spreaders for organic manures
Why should I calibrate my manure spreader?
The uneven application of manure can result in variable supply of nutrients to the crop that is difficult to take into account as part of the farm nutrient management plan; so farmers tend to use fertiliser to meet crop nutrient needs at under applied rates.
Full calibration procedures determine the application rate achievable by the spreader and how evenly slurry or solid manure is distributed.
It is important to ascertain how much manure or slurry you are spreading in any one field in order to complete accurate nutrient planning. If you can calculate the application rate, then you are more likely to make sure that you are compliant with any legislation, as well as targeting nutrients to times of year and areas of the farm that will return the most yield and cost savings.
Calibrating slurry spreaders
The application rate is affected by three factors:
- Discharge rate
- Bout width
- Forward speed
Once the target application rate has been determined based on crop requirements and available nutrients in the slurry you can calculate the required forward speed to achieve the application rate.
Vacuum / pumped tanker
The discharge rate can be determined by filing the tanker of a known volume to its maximum capacity and timing how long the tanker takes to empty under normal conditions that would be used when spreading.
Alternatively tankers could be weighed both full and empty at a local weighbridge or an on-farm vehicle weighing system to determine its capacity.
Pumped tankers / umbilical systems / irrigators that are all fitted with a positive displacement pump
Manufacturers can supply pump performance charts from which discharge rates can be determined.
Use a flow meter to determine discharge rate as the flow rate will vary with distance and height pumped and with variations in slurry physical characteristics.
Band spreaders, trailing show and injection systems
The bout width can be defined as the width of the boom or injector toolbar
With broadcast spreaders it is much more difficult to determine the bout width. Because the distribution of slurry across the full spreading width of a broadcasting spreader is not usually even, it is important to overlap the bouts to achieve a low coefficient of variation. As a general rule, bout width should be half the spreading width.
Calibrating solid manure (FYM) spreaders
Application rate is affected by three factors:
- Discharge rate
- Bout width
- Forward speed
The discharge rate of solid manure spreaders can be determined by timing how long the spreader takes to empty a complete load.
- Weigh the spreader both full and empty at a local weighbridge or on a farm vehicle weighing system to calculate the weight of the manure
- For rear discharge spreaders the spread pattern is usually quite even and the bout width can be taken as the spreading width.
- For both types of side discharge spreader it is much more difficult to establish the bout width.
- Generally the narrower the bout width, the lower the coefficient of variation but as a general rule the bout width should be half the spreading width.
Good practice spreading guidelines
For both slurry and solid manures a cross check can be made by counting the number of tanker spreader loads and multiplying it by its capacity (m3 or tonnes) to give the amount distributed on the field of a known area.
These tests are not a substitute for comprehensive machine calibration but they will give a good indication of on farm performance and will allow better use of available nutrients.
Stirring slurry stores, just before spreading will help ensure a more even application of nutrients.
Adjust discharge from the spreader so that the spreading trajectory is low and manure is not being thrown high in the air as this will increase nutrient losses as well as inaccurate spreading.