Crop sprayers continue to develop and the basic principle remains. A liquid solution is delivered through a precisely shaped nozzle, at a set pressure to deliver a distribution of droplets on the target plant, weed or soil.
Modern sprayers can do this more accurately and with a greater degree of control than before. The concept of precision spraying using SMART sprayers promises even more-targeted application with the potential to reduce pesticide use and lessen resistance development while retaining efficacy.
Precision in spraying has been continuously improving with the help of:
Better nozzle spray patterns.Accurate pressure monitoring and forward speed measurement.The use of air-induction nozzles to reduce drift.Angled nozzles to alter coverage on certain targets.Boom height control systems to reduce drift.Auto-switching of sections or nozzles at headlands and short bouts, to minimise overlap.Sprayer control systems to ease setting and control output.Smartphone spraying apps to help select nozzle, speed and pressure.
An example of the degree of collaboration needed to deliver more precise spraying in can be seen in Amazone's recent announcement of their SMART sprayer trials where three companies are involved in the on-board technology.
While conventional spraying strives to apply the product evenly across an entire field, a SMART/precision approach is more targeted.
Here, the objective is to only apply the chemical on plants or parts of the field that would benefit from it and at appropriate rates. This level of precision needs at least three essential components:
1. A sensing system, which can measure differences in crop, soil or weed, forming the basis for variable application or spot treatment. These sensors could assess vegetation, or occasionally soil, and they can be tractor-mounted, drone-mounted, satellite-based or indeed held by a user. Data from a combination of sensors and other sources, such as yield or soil maps or manual verification of weeds (ground truthing), can be used to give more information on the cause of any variation seen.2. A response function based on research, which determines what is to be done. If a weed area is identified, it is sprayed with herbicide. But if a disease focus is identified, meteorological data and modelling may be used to determine if only that focus is treated or the entire field. 3. Spraying technology that allows the rate to be varied or product to be added to respond to demands for variable rate or spot spraying. This needs to be done fast enough and at a resolution (ie treated width or area) that matches that of the information provided.The resulting application can be divided into three categories:
Variable rate application:this involves changing the rate of the product being applied based on measured variability.
The resolution or size of the area over which this variability is applied will depend on the measuring and/or application technology.
The minimum may be the complete boom width, eg 24m wide, or it could be part boom widths, or smaller, if nozzle outputs can be controlled individually.
Patch spraying: this is where specific areas of the field, perhaps where weeds are present or a disease focus is identified, are sprayed with a particular product when other areas are not treated.
Spot spraying: this is like patch spraying except it implies that the spray can be targeted to a much smaller area and may be targeting a single weed for example.
Variability sensors
While there are many characteristics of crop and soil that can be measured, those that are used in real-time are often “multi-spec” or “RGB” image sensors which measure part of the electromagnetic spectrum that we see as colour but it includes non-visible wavelengths. LIDAR distance-type sensors are also used.
By fine-tuning what is measured, this data can be used to identify the presence of plants, perhaps identify the plant types (weed or crop), and even measure plant stress (disease or drought).
Assessing shape and patterns (machine vision) can also identify plant types.
Nozzles and control technology
Fan nozzles, whether air-induction or standard, are versatile and suit uniform application. However, they are quite limited for variable rate application.
Using spray pressure to alter rate negatively affects spray quality, drift and crop penetration. Changing forward speed will change application rate, but this affects work rate and can only work across the entire boom width (12m to 36m). Three newer nozzle technologies give improved variable rate control options:
Variable rate nozzles with in-nozzle mechanical metering.Multi-nozzle switching options at each nozzle position.Pulse width modulation (PWM) control at each nozzle.Mechanical metering nozzle
These nozzle bodies have a variable orifice, usually controlled by the sprayer pressure, which increases as pressure increases.
A doubling of pressure from two- to four-bar with a conventional nozzle may increase spray output by just 40%. But with a “Varitarget” variable orifice nozzle that pressure change would give a 350% increase in output.
However, these nozzle types struggle to maintain the degree of output control required for precise fungicide or herbicide use.
Another variant, the Turbodrop variable rate, has one orifice spraying continuously, with a second orifice opening when pressure is increased.
Nozzle types which rely on pressure change to vary the opening need very good pressure control systems. They have not had a lot of application in Europe.
Multi-nozzle switching options
at each nozzle point
Examples of this increasingly available technology include Exactapply (John Deere), Amaselect (Amazone), Seletron (Arag) and Duo react (Hypro).
These automatic switching nozzle holder units can have up to five nozzles of different size. They are controlled electronically and can switch instantaneously to reflect the required output changes.
While the spraying pressure remains constant across the boom, the availability of, say, 02, 03, 04 and 05 size nozzles – available to work singly or in combination – allows a range of outputs to be automatically selected at each nozzle point, giving the possibility of variable rate application at each individual nozzle position.
In addition, this system can compensate for differences in boom speed as it turns a corner or curve.
Pulse width modulation (PWM)
The concept of PWM sprayer control is quite simple. Instead of the spray flowing continuously through the nozzle, it can be “pulsed” through it to reduce the flow.
The term, “pulse width modulation”, comes from the electronic control circuit used, which is more typically used to control electric motor speeds.
In a spraying application, the pulses may occur at 10Hz up to 100Hz, ie 10 to 100 times per second. At maximum flow, the nozzle is spraying continuously but at 50% flow, the nozzle is only open half of the time (50% duty cycle).
So for each pulse, it is on and off for equal lengths of time, but there are 10 to 100 pulses per second.
These systems typically allow for a four- or five-fold change in output, eg from 200l/ha down to 50l/ha. The spray line and solenoid system must hold the system pressure perfectly to ensure each short pulse delivers a proper spray pattern at the instant that it is spraying.
Typically, every second nozzle is working on the opposite phase so when one is pulsing on, the adjacent nozzle is off, which reduces the risk of crop being “missed” at low duty-cycle rates and higher forward speeds.
The higher pulse rates (20hz to 100hz) reduce the risk of missed crop. This system is well suited to variable rate application as it can maintain spray quality (droplet size, penetration and coverage) across a range of outputs and the instantaneous on-off and individual nozzle control that the system allows is particularly suited to spot spraying.
However, PWM does not work well with air induction nozzles.
There are a number of manufacturers working on, or offering PWM systems including Teejet, Amazone, Raven and Agrifac.
Different products
on a variable basis
Where a SMART spraying system requires additional spray products (eg additional herbicide) rather than just a variable rate, to be added for spot-spraying or patch-spraying, there are a number of delivery options possible:
Separate spray pass: the sprayer delivers the main product first and then delivers the additional product in a separate run-in “patch” or “spot” spray mode using the necessary sensor/map-based control technology.Multi-line systems: this requires a completely separate spray line system (including separate nozzles and spray tank) on the boom and would typically have a spray line delivering an overall product at a constant application rate, and then; a spot or patch treatment line complete with necessary sensor/map-based control technology, to deliver a second product at a variable rate to spots or patches within fields. Dosing or direct injection system: in this system, the undiluted pesticide products are held separately from the diluent (water) which is circulating through the spray line. The pesticide products are accurately metered into the supply while spraying with very precise metering and mixing equipment.
This would typically follow an application map applying fungicide at a constant rate and adding herbicide as determined by the controlling application map.
While this allows almost endless mixing and application possibilities, it is complex, expensive and involves handling of undiluted product.
Also, it is more suited to patch spraying than spot spraying as it cannot instantly deliver the required product to a single nozzle.
However, there are advantages in a patch spraying system and companies such as Raven and Diimotion have developed these systems.
Drone delivery: the hype around drones continues in agriculture and is justified in many areas. In precision approaches, the drone’s ability to carry cameras/multi-spec sensors is useful, but drones could potentially deliver and apply pesticide to patches or perhaps to spots where a field requires a very small amount of patch or spot spraying.
For example, if a 10ha field needed 1% of the area sprayed for a developing grass weed problem, with a product applied at 50 l/ha, it would require a drone with a payload of 5kg to do this with one fill.
Bringing it
all together
The precision spraying concepts discussed here have existed for at least 30 years. However, development has been slow as it relies on research on sensors, positioning, data processing (including machine learning/artificial intelligence), response models/algorithms and sprayer control, to bring these concepts to a working model.
While there has been progress on individual components, we are only now seeing complete systems being put together in configurations that may result in large-scale application in the future.
Amazone’s recent announcement of field trials with a SMART sprayer indicates the level of collaboration necessary to bring the technologies together.
Amazone produces the sprayer and its controls. Bosch produces the camera sensor used to scan the crop and identify the weeds and Xarvio, a BASF company, provides the software that determines the sprayer response.
The sprayer uses PWM to allow accurate application on a spot basis to the identified weeds and a conventional sprayer line is available for simultaneous overall spraying with a separate product.
While these three commercial companies are working together on this smart sprayer, the technologies being built on had their origins in many university and research Institute projects.
Many research and commercial groups continue to work on these technologies.
Key points
Smart sprayers and spraying will inevitably feature more in the coming years.The ability to alter application amount at each nozzle point will provide the ability to increase or decrease rate for a specific travel distance.This will provide the option to patch spray or spot spray, as well as to vary rate in a given area. Making such systems work will require many different technologies to work to a similar level of technical accuracy and competency.
Crop sprayers continue to develop and the basic principle remains. A liquid solution is delivered through a precisely shaped nozzle, at a set pressure to deliver a distribution of droplets on the target plant, weed or soil.
Modern sprayers can do this more accurately and with a greater degree of control than before. The concept of precision spraying using SMART sprayers promises even more-targeted application with the potential to reduce pesticide use and lessen resistance development while retaining efficacy.
Precision in spraying has been continuously improving with the help of:
Better nozzle spray patterns.Accurate pressure monitoring and forward speed measurement.The use of air-induction nozzles to reduce drift.Angled nozzles to alter coverage on certain targets.Boom height control systems to reduce drift.Auto-switching of sections or nozzles at headlands and short bouts, to minimise overlap.Sprayer control systems to ease setting and control output.Smartphone spraying apps to help select nozzle, speed and pressure.
An example of the degree of collaboration needed to deliver more precise spraying in can be seen in Amazone's recent announcement of their SMART sprayer trials where three companies are involved in the on-board technology.
While conventional spraying strives to apply the product evenly across an entire field, a SMART/precision approach is more targeted.
Here, the objective is to only apply the chemical on plants or parts of the field that would benefit from it and at appropriate rates. This level of precision needs at least three essential components:
1. A sensing system, which can measure differences in crop, soil or weed, forming the basis for variable application or spot treatment. These sensors could assess vegetation, or occasionally soil, and they can be tractor-mounted, drone-mounted, satellite-based or indeed held by a user. Data from a combination of sensors and other sources, such as yield or soil maps or manual verification of weeds (ground truthing), can be used to give more information on the cause of any variation seen.2. A response function based on research, which determines what is to be done. If a weed area is identified, it is sprayed with herbicide. But if a disease focus is identified, meteorological data and modelling may be used to determine if only that focus is treated or the entire field. 3. Spraying technology that allows the rate to be varied or product to be added to respond to demands for variable rate or spot spraying. This needs to be done fast enough and at a resolution (ie treated width or area) that matches that of the information provided.The resulting application can be divided into three categories:
Variable rate application:this involves changing the rate of the product being applied based on measured variability.
The resolution or size of the area over which this variability is applied will depend on the measuring and/or application technology.
The minimum may be the complete boom width, eg 24m wide, or it could be part boom widths, or smaller, if nozzle outputs can be controlled individually.
Patch spraying: this is where specific areas of the field, perhaps where weeds are present or a disease focus is identified, are sprayed with a particular product when other areas are not treated.
Spot spraying: this is like patch spraying except it implies that the spray can be targeted to a much smaller area and may be targeting a single weed for example.
Variability sensors
While there are many characteristics of crop and soil that can be measured, those that are used in real-time are often “multi-spec” or “RGB” image sensors which measure part of the electromagnetic spectrum that we see as colour but it includes non-visible wavelengths. LIDAR distance-type sensors are also used.
By fine-tuning what is measured, this data can be used to identify the presence of plants, perhaps identify the plant types (weed or crop), and even measure plant stress (disease or drought).
Assessing shape and patterns (machine vision) can also identify plant types.
Nozzles and control technology
Fan nozzles, whether air-induction or standard, are versatile and suit uniform application. However, they are quite limited for variable rate application.
Using spray pressure to alter rate negatively affects spray quality, drift and crop penetration. Changing forward speed will change application rate, but this affects work rate and can only work across the entire boom width (12m to 36m). Three newer nozzle technologies give improved variable rate control options:
Variable rate nozzles with in-nozzle mechanical metering.Multi-nozzle switching options at each nozzle position.Pulse width modulation (PWM) control at each nozzle.Mechanical metering nozzle
These nozzle bodies have a variable orifice, usually controlled by the sprayer pressure, which increases as pressure increases.
A doubling of pressure from two- to four-bar with a conventional nozzle may increase spray output by just 40%. But with a “Varitarget” variable orifice nozzle that pressure change would give a 350% increase in output.
However, these nozzle types struggle to maintain the degree of output control required for precise fungicide or herbicide use.
Another variant, the Turbodrop variable rate, has one orifice spraying continuously, with a second orifice opening when pressure is increased.
Nozzle types which rely on pressure change to vary the opening need very good pressure control systems. They have not had a lot of application in Europe.
Multi-nozzle switching options
at each nozzle point
Examples of this increasingly available technology include Exactapply (John Deere), Amaselect (Amazone), Seletron (Arag) and Duo react (Hypro).
These automatic switching nozzle holder units can have up to five nozzles of different size. They are controlled electronically and can switch instantaneously to reflect the required output changes.
While the spraying pressure remains constant across the boom, the availability of, say, 02, 03, 04 and 05 size nozzles – available to work singly or in combination – allows a range of outputs to be automatically selected at each nozzle point, giving the possibility of variable rate application at each individual nozzle position.
In addition, this system can compensate for differences in boom speed as it turns a corner or curve.
Pulse width modulation (PWM)
The concept of PWM sprayer control is quite simple. Instead of the spray flowing continuously through the nozzle, it can be “pulsed” through it to reduce the flow.
The term, “pulse width modulation”, comes from the electronic control circuit used, which is more typically used to control electric motor speeds.
In a spraying application, the pulses may occur at 10Hz up to 100Hz, ie 10 to 100 times per second. At maximum flow, the nozzle is spraying continuously but at 50% flow, the nozzle is only open half of the time (50% duty cycle).
So for each pulse, it is on and off for equal lengths of time, but there are 10 to 100 pulses per second.
These systems typically allow for a four- or five-fold change in output, eg from 200l/ha down to 50l/ha. The spray line and solenoid system must hold the system pressure perfectly to ensure each short pulse delivers a proper spray pattern at the instant that it is spraying.
Typically, every second nozzle is working on the opposite phase so when one is pulsing on, the adjacent nozzle is off, which reduces the risk of crop being “missed” at low duty-cycle rates and higher forward speeds.
The higher pulse rates (20hz to 100hz) reduce the risk of missed crop. This system is well suited to variable rate application as it can maintain spray quality (droplet size, penetration and coverage) across a range of outputs and the instantaneous on-off and individual nozzle control that the system allows is particularly suited to spot spraying.
However, PWM does not work well with air induction nozzles.
There are a number of manufacturers working on, or offering PWM systems including Teejet, Amazone, Raven and Agrifac.
Different products
on a variable basis
Where a SMART spraying system requires additional spray products (eg additional herbicide) rather than just a variable rate, to be added for spot-spraying or patch-spraying, there are a number of delivery options possible:
Separate spray pass: the sprayer delivers the main product first and then delivers the additional product in a separate run-in “patch” or “spot” spray mode using the necessary sensor/map-based control technology.Multi-line systems: this requires a completely separate spray line system (including separate nozzles and spray tank) on the boom and would typically have a spray line delivering an overall product at a constant application rate, and then; a spot or patch treatment line complete with necessary sensor/map-based control technology, to deliver a second product at a variable rate to spots or patches within fields. Dosing or direct injection system: in this system, the undiluted pesticide products are held separately from the diluent (water) which is circulating through the spray line. The pesticide products are accurately metered into the supply while spraying with very precise metering and mixing equipment.
This would typically follow an application map applying fungicide at a constant rate and adding herbicide as determined by the controlling application map.
While this allows almost endless mixing and application possibilities, it is complex, expensive and involves handling of undiluted product.
Also, it is more suited to patch spraying than spot spraying as it cannot instantly deliver the required product to a single nozzle.
However, there are advantages in a patch spraying system and companies such as Raven and Diimotion have developed these systems.
Drone delivery: the hype around drones continues in agriculture and is justified in many areas. In precision approaches, the drone’s ability to carry cameras/multi-spec sensors is useful, but drones could potentially deliver and apply pesticide to patches or perhaps to spots where a field requires a very small amount of patch or spot spraying.
For example, if a 10ha field needed 1% of the area sprayed for a developing grass weed problem, with a product applied at 50 l/ha, it would require a drone with a payload of 5kg to do this with one fill.
Bringing it
all together
The precision spraying concepts discussed here have existed for at least 30 years. However, development has been slow as it relies on research on sensors, positioning, data processing (including machine learning/artificial intelligence), response models/algorithms and sprayer control, to bring these concepts to a working model.
While there has been progress on individual components, we are only now seeing complete systems being put together in configurations that may result in large-scale application in the future.
Amazone’s recent announcement of field trials with a SMART sprayer indicates the level of collaboration necessary to bring the technologies together.
Amazone produces the sprayer and its controls. Bosch produces the camera sensor used to scan the crop and identify the weeds and Xarvio, a BASF company, provides the software that determines the sprayer response.
The sprayer uses PWM to allow accurate application on a spot basis to the identified weeds and a conventional sprayer line is available for simultaneous overall spraying with a separate product.
While these three commercial companies are working together on this smart sprayer, the technologies being built on had their origins in many university and research Institute projects.
Many research and commercial groups continue to work on these technologies.
Key points
Smart sprayers and spraying will inevitably feature more in the coming years.The ability to alter application amount at each nozzle point will provide the ability to increase or decrease rate for a specific travel distance.This will provide the option to patch spray or spot spray, as well as to vary rate in a given area. Making such systems work will require many different technologies to work to a similar level of technical accuracy and competency. 
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