The physical form or quality of fertilizer can have a huge effect on how evenly it spreads, particularly at wider bout widths. But what are the important factors? Is it the manufacturing process or particle density, size or shape? This article examines how the physical quality of fertilizer can affect how evenly it spreads.
Today’s fertilizer spreaders are all broadcaster type, which spread fertilizer over a fairly wide bout width (6m to 36m wide) from a disc or spout that is directly behind the tractor.
All broadcast spreaders produce a wide tapered spread pattern that must overlap the previous run to give an even distribution. A 12m spreader will frequently spread fertilizer more than 24m with fertilizer visible in the next tramline.
Depending on the spreader and bout width, individual particles of fertilizer may have to be thrown between 12m and 30m from the spreader and land in the right place; a huge challenge often compounded by wind and bumpy fields.
Spreading width
The following factors determine the spread pattern of a fertilizer spreader:
The design of the spreading disc and its vanes (length, shape, angle etc) and of the delivery point of the fertilizer to the disc/vane.The physical characteristics of the fertilizer (size, shape, density, strength of granule).The setting of the machine (choice of disc, disc speed, vane, vane angle, fertilizer drop point, spreader height and angle.Field conditions, particularly wind.How it works
So, how does fertilizer get thrown this distance? The spreader vane has to transmit enough energy to the fertilizer particle to allow it travel through the air, in the correct direction, for the required distance. Disc and vane design is focused on accelerating the fertilizer particle and causing it to leave the vane in the correct flight path, typically at fast peripheral vane speeds.
Flat trajectories (flight paths) are stable but require an adequate clearance over the crop. Some spreaders use an upward trajectory to make the distance, but throwing fertilizer upwards leaves it prone to wind as it drops with less energy at the outer part of the spread width.
To spread evenly at different bout widths with different fertilizers often requires careful setting or adjustment of the machine. Vane type and position, disc speed, fertilizer drop point, etc, can be used to modify the way the fertilizer is thrown to optimise the pattern with different fertilizers and at different target bout widths – 18m rather than 12m, for example.
Quality and the machine
Fertilizer quality can play a huge role in achieving even fertilizer spreading. The effect of fertilizer depends on the type (including specific model) of fertilizer spreader and the bout width used. Some spreaders are ‘forgiving’ having a strongly overlapped, tapered spread pattern that gives even spreading at widths up to 15m or 18m with a range of fertilizers.
Other machines struggle with anything other than good quality fertilizer and require careful setting even at modest 12m to 15m bout widths.
Indeed, some may not be able to spread poorer quality fertilizer at wider bout widths. Where fertilizer is spread at 24m or more, its quality affects the performance of all spreaders.
Fertilizers are manufactured by different processes. Some are simply broken stone while others, produced by different manufacturing processes, can vary from being almost rounded and regular-shaped to being quite irregular.
Prills are generally rounded and regular in shape. There is occasionally debate as to whether prills or regularly-shaped granules spread better. In this case, the wrong question is being asked.
What is important is the density and size distribution of the particles, as these will be the main determinants of the spreadability of the products. Both prills and granules can vary in density and size.
If the density and size distribution of a prilled product are the same as a granular product, it will spread at least as well as the granular product.
If the granular product is irregular-shaped, on some machines the prilled product is likely to produce a better spread pattern if its density and size distribution are the same.
The question is not whether a product is prilled or granular but spreadability is influenced by:
Density: The higher the better.Size distribution: Generally, bigger is better with as little as possible below 2mm diameter.Strength: Stronger is better.Shape: Regular and/or rounded are better.Drop the doubt
Some of the doubts that people have about prilled fertilizer is their association with specific products. For instance, urea is commonly sold as small prills. With just 80% of the density of other fertilizers and a small size distribution, these are difficult to spread evenly at anything other than modest bout widths.
But this is not because they are prills. It is because of their size distribution and density. Similarly, some imported prilled CAN products had a small size distribution and, as a result, were challenging to spread at wide bout widths. Again, this was due to their size distribution and not because they were prills.
Finally
Spreading fertilizer evenly at wide bout widths (over 18m) is challenging.
Physical fertilizer quality, in combination with appropriate machine selection and correct spreader setting, is important to help achieve even spreading. Whether a fertilizer is prilled or granular has little effect on spreadability.
The four factors that are important are:
Density of the fertilizer.Size of the granules.Shape of the granule.Strength of granule.Density of the fertilizer
Dense fertilizers are easier to throw.
Think of a golf ball which is relatively dense and a table tennis ball which is of similar size but a fraction of the density.
We can transfer a lot of energy into the golf ball, allowing us to throw it some distance, where its weight and speed easily overcomes the wind resistance for quite a distance.
But with nothing to capture the energy in the table-tennis ball, wind resistance soon stops it.
With fertilizer, urea products are at a disadvantage because they are only 80% of the density of most other types of fertilizer.
They are not impossible to throw by any means, but they are more of a challenge and require a good fertilizer spreader set correctly to throw the distance.
The spreading ability of low density products can be improved by having a good size distribution; bigger urea granules will spread better than smaller ones.
Size of the granules
The size of the fertilizer particle is important. At the extreme, it is impossible to throw dust.
For material of a common density, larger particles will be easier to throw further as each individual particle can capture more energy when accelerated by the disc and, as a result, is capable of being accurately thrown a distance.
In practice, there is a limit to useful size as large particles may not flow very well. They would result in less granules spread per square metre of field.
Particle size distributions with the majority of particles (80%) in the 2mm to 4mm range will usually allow a good spread to be achieved.
Less of the smaller size (most from 3mm to 4.5mm diameter) would usually make it easier to achieve wider spread widths provided the individual particles are strong.
Where fertilizer blends containing more than one element are used, the size distribution and density of the components should be similar to avoid segregation across the spread width, resulting in elements of the blend being unevenly spread.
Simple handheld sieve boxes available from manufacturers can indicate a fertilizer’s size distribution.
A fertilizer supplier should also have a spec sheet that includes size distribution.
Shape of the granule
Fertilizer particle shape will affect the movement of fertilizer along the disc and vane and its flow through the air.
Rounded particles may move along the vane more smoothly and predictably and will probably travel through the air more predictably than irregular-shaped particles.
For most variations in shape though, this would not be a large factor.
Differences in density and size would have a greater effect.
However, with some machines irregular shapes would not spread as well as rounded particles. Many spreader manufacturers use characteristic photographs to classify fertilizer particle shape.
Strength of granule
Particle strength is important to prevent them from being broken on impact by the high speed vanes on modern fertilizer spreaders.
If the granule breaks, the spreader is trying to spread a range of smaller particle sizes down to dust.
Particle strength is more important today than it was in the past. A simple individual particle strength tester is now available from many fertilizer spreader manufacturers.
Know your spreader’s limitations in terms of bout width and how well it copes with fertilizer of different physical quality. Ensure you purchase fertilizer of suitable physical quality and that you set the spreader correctly for the fertilizer and bout width. Fertilizer suppliers should be asked for specification sheets, which indicate the size distribution and density of the product. Consider this when making a purchase decision. Don’t necessarily choose the cheapest product. Most spreader manufacturers have detailed setting charts available online or in setting manuals which are increasingly based on size distribution, density, particle strength and shape. Sieve boxes, strength and density testers and shape guides are all available from manufacturers. While these will help get the best pattern from different quality fertilizers, it is important to note that fertilizer quality will still affect evenness, particularly at wider bout widths.
The physical form or quality of fertilizer can have a huge effect on how evenly it spreads, particularly at wider bout widths. But what are the important factors? Is it the manufacturing process or particle density, size or shape? This article examines how the physical quality of fertilizer can affect how evenly it spreads.
Today’s fertilizer spreaders are all broadcaster type, which spread fertilizer over a fairly wide bout width (6m to 36m wide) from a disc or spout that is directly behind the tractor.
All broadcast spreaders produce a wide tapered spread pattern that must overlap the previous run to give an even distribution. A 12m spreader will frequently spread fertilizer more than 24m with fertilizer visible in the next tramline.
Depending on the spreader and bout width, individual particles of fertilizer may have to be thrown between 12m and 30m from the spreader and land in the right place; a huge challenge often compounded by wind and bumpy fields.
Spreading width
The following factors determine the spread pattern of a fertilizer spreader:
The design of the spreading disc and its vanes (length, shape, angle etc) and of the delivery point of the fertilizer to the disc/vane.The physical characteristics of the fertilizer (size, shape, density, strength of granule).The setting of the machine (choice of disc, disc speed, vane, vane angle, fertilizer drop point, spreader height and angle.Field conditions, particularly wind.How it works
So, how does fertilizer get thrown this distance? The spreader vane has to transmit enough energy to the fertilizer particle to allow it travel through the air, in the correct direction, for the required distance. Disc and vane design is focused on accelerating the fertilizer particle and causing it to leave the vane in the correct flight path, typically at fast peripheral vane speeds.
Flat trajectories (flight paths) are stable but require an adequate clearance over the crop. Some spreaders use an upward trajectory to make the distance, but throwing fertilizer upwards leaves it prone to wind as it drops with less energy at the outer part of the spread width.
To spread evenly at different bout widths with different fertilizers often requires careful setting or adjustment of the machine. Vane type and position, disc speed, fertilizer drop point, etc, can be used to modify the way the fertilizer is thrown to optimise the pattern with different fertilizers and at different target bout widths – 18m rather than 12m, for example.
Quality and the machine
Fertilizer quality can play a huge role in achieving even fertilizer spreading. The effect of fertilizer depends on the type (including specific model) of fertilizer spreader and the bout width used. Some spreaders are ‘forgiving’ having a strongly overlapped, tapered spread pattern that gives even spreading at widths up to 15m or 18m with a range of fertilizers.
Other machines struggle with anything other than good quality fertilizer and require careful setting even at modest 12m to 15m bout widths.
Indeed, some may not be able to spread poorer quality fertilizer at wider bout widths. Where fertilizer is spread at 24m or more, its quality affects the performance of all spreaders.
Fertilizers are manufactured by different processes. Some are simply broken stone while others, produced by different manufacturing processes, can vary from being almost rounded and regular-shaped to being quite irregular.
Prills are generally rounded and regular in shape. There is occasionally debate as to whether prills or regularly-shaped granules spread better. In this case, the wrong question is being asked.
What is important is the density and size distribution of the particles, as these will be the main determinants of the spreadability of the products. Both prills and granules can vary in density and size.
If the density and size distribution of a prilled product are the same as a granular product, it will spread at least as well as the granular product.
If the granular product is irregular-shaped, on some machines the prilled product is likely to produce a better spread pattern if its density and size distribution are the same.
The question is not whether a product is prilled or granular but spreadability is influenced by:
Density: The higher the better.Size distribution: Generally, bigger is better with as little as possible below 2mm diameter.Strength: Stronger is better.Shape: Regular and/or rounded are better.Drop the doubt
Some of the doubts that people have about prilled fertilizer is their association with specific products. For instance, urea is commonly sold as small prills. With just 80% of the density of other fertilizers and a small size distribution, these are difficult to spread evenly at anything other than modest bout widths.
But this is not because they are prills. It is because of their size distribution and density. Similarly, some imported prilled CAN products had a small size distribution and, as a result, were challenging to spread at wide bout widths. Again, this was due to their size distribution and not because they were prills.
Finally
Spreading fertilizer evenly at wide bout widths (over 18m) is challenging.
Physical fertilizer quality, in combination with appropriate machine selection and correct spreader setting, is important to help achieve even spreading. Whether a fertilizer is prilled or granular has little effect on spreadability.
The four factors that are important are:
Density of the fertilizer.Size of the granules.Shape of the granule.Strength of granule.Density of the fertilizer
Dense fertilizers are easier to throw.
Think of a golf ball which is relatively dense and a table tennis ball which is of similar size but a fraction of the density.
We can transfer a lot of energy into the golf ball, allowing us to throw it some distance, where its weight and speed easily overcomes the wind resistance for quite a distance.
But with nothing to capture the energy in the table-tennis ball, wind resistance soon stops it.
With fertilizer, urea products are at a disadvantage because they are only 80% of the density of most other types of fertilizer.
They are not impossible to throw by any means, but they are more of a challenge and require a good fertilizer spreader set correctly to throw the distance.
The spreading ability of low density products can be improved by having a good size distribution; bigger urea granules will spread better than smaller ones.
Size of the granules
The size of the fertilizer particle is important. At the extreme, it is impossible to throw dust.
For material of a common density, larger particles will be easier to throw further as each individual particle can capture more energy when accelerated by the disc and, as a result, is capable of being accurately thrown a distance.
In practice, there is a limit to useful size as large particles may not flow very well. They would result in less granules spread per square metre of field.
Particle size distributions with the majority of particles (80%) in the 2mm to 4mm range will usually allow a good spread to be achieved.
Less of the smaller size (most from 3mm to 4.5mm diameter) would usually make it easier to achieve wider spread widths provided the individual particles are strong.
Where fertilizer blends containing more than one element are used, the size distribution and density of the components should be similar to avoid segregation across the spread width, resulting in elements of the blend being unevenly spread.
Simple handheld sieve boxes available from manufacturers can indicate a fertilizer’s size distribution.
A fertilizer supplier should also have a spec sheet that includes size distribution.
Shape of the granule
Fertilizer particle shape will affect the movement of fertilizer along the disc and vane and its flow through the air.
Rounded particles may move along the vane more smoothly and predictably and will probably travel through the air more predictably than irregular-shaped particles.
For most variations in shape though, this would not be a large factor.
Differences in density and size would have a greater effect.
However, with some machines irregular shapes would not spread as well as rounded particles. Many spreader manufacturers use characteristic photographs to classify fertilizer particle shape.
Strength of granule
Particle strength is important to prevent them from being broken on impact by the high speed vanes on modern fertilizer spreaders.
If the granule breaks, the spreader is trying to spread a range of smaller particle sizes down to dust.
Particle strength is more important today than it was in the past. A simple individual particle strength tester is now available from many fertilizer spreader manufacturers.
Know your spreader’s limitations in terms of bout width and how well it copes with fertilizer of different physical quality. Ensure you purchase fertilizer of suitable physical quality and that you set the spreader correctly for the fertilizer and bout width. Fertilizer suppliers should be asked for specification sheets, which indicate the size distribution and density of the product. Consider this when making a purchase decision. Don’t necessarily choose the cheapest product. Most spreader manufacturers have detailed setting charts available online or in setting manuals which are increasingly based on size distribution, density, particle strength and shape. Sieve boxes, strength and density testers and shape guides are all available from manufacturers. While these will help get the best pattern from different quality fertilizers, it is important to note that fertilizer quality will still affect evenness, particularly at wider bout widths. 
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