The self-propelled sprayer revolution is complete in western Canada. Almost all sales of new equipment are self-propelled. In fact, the once thriving sector of Canadian-made pull-type sprayers, and the innovations they brought to spraying, has disappeared.
In its place we have self-propelled sprayers that offer plenty of power, large tanks, high mobility and comfort, and of course, the clearance required for late-season sprays. These features come at a cost: high capital expense, weight, fuel consumption and drift potential if the speed or boom height are not controlled.
The self-propelled machines are nice; however, customers are becoming concerned about overall value. Sure, the sprayer is the most-used piece of equipment on the farm, with the average field being treated four to five times per year. Does that justify the $500 to $700 k purchase price?
To answer this question, we need to evaluate the alternatives. Even though we’ve lost most North American pull-type sprayer makers, a few, such as Top Air, are left. A new pull type, the Connect Sniper, is being offered by Pattison Liquid. In addition, there are now several European manufacturers looking at our market. These bring large capacity, sophisticated booms plumbing and a narrow transport width. Let’s look at the issues:
The Connect Sniper, manufactured by Pattison Liquid, offers recirculating booms, Raven Hawkeye pulse-width modulation, continuous rinsing, and 120′ Millenium booms. The WEEDit spot spray system is also available.
Capacity
Not a problem. Top Air features tanks up to 2400 gallons and 132’ booms. Amazone builds a 3000 gallon tank twin axle sprayer (UX11200) with 132’ booms. The 230 gpm on-board diaphragm pump can fill the sprayer in 15 minutes. The Hardi Commander offers tanks up to 2600 gallons with 132’ booms. The Horsch Leeb TD12 is at 3170 gallons with 138’ booms. Equipped with air brakes, these sprayers can be trailed at up to 50 km/h.
The Amazone UX 11200 has an 11,200 L (2960 US gal) tank and tandem, steering axles combined with up to 130′ booms.
Clearance
The pull-types themselves have adequate clearance for most crops. The limiting factor will be the tractor and the hitch point. The availability of a high hitch point, and an 80 mm ball, on European tractors, is a boon for this. Although it may be necessary to shield the low standard drawbar and belly, pull-type owners report no long-term effects from the lower clearance.
The Horsch Leeb TD12 offers a 12,000 L (3170 US gal) tank and up to 1.25 m ground clearance (Photo: Horsch.com).European tractors offer 80 mm ball hitches for larger implements with high mounting heights to gain extra sprayer clearance.
Tractor
The pull-type sprayer makes most sense if it allows the re-purposing of an existing tractor. The common yard tractor isn’t enough, as the high capacity sprayers may require >200 hp with front wheel assist, especially in softer ground or hilly terrain. Another requirement is that the track width match the sprayer, and the European standard of a 2.25 m track width (centre to centre) can be hard to match in North America. New rims on the sprayer can push the width out, but the resulting increased axle stress may be problematic; these issues should be considered in advance. Fortunately, powerful front wheel assist tractors are finding a place on farms, even as seeding tractors. The changing over from one implement to another during a busy time can be a hassle, with a dedicated rate controller requiring additional cab real estate. But with the lower capital cost of a pull-type, a new tractor that also has other utility on the farm may be justified.
Large pull types require large tractors that may not already exist on the farm. The ability to match wheel tracks and the convenience of monitor hookups are important considerations.
Productivity
We’ve long maintained that productivity gain through increased travel speed creates more problems than it solves. It is virtually unavoidable to use somewhat higher booms with faster speeds, and it’s been proven that spray drift potential increases with travel speed. Instead, the sprayer features that save time are faster fill and clean times (reduced downtime), larger tanks (fewer stops to fill) and wider booms. Wider booms are easier to keep steady with slower moving equipment.
So how do typical self-propelled sprayers stack up against pull-types?
We compared two sprayers, a large pull-type with 3000 US gallon tank and a typical self-propelled with a 1200 gallon tank. Travel speeds were 10 and 15 mph, respectively, and fill times were 15 and 10 minutes. The slower pull-type turned in one headland, whereas the self-propelled used two to allow room for acceleration after the turn.
On half-mile runs, our “Productivity Calculator” at agrimetrixapps.com showed 129 acres per hour for the self-propelled and a respectable 119 acres/h for the pull type. The value of fast but infrequent fills and the more efficient turns made the difference for the pull-type. Use the app to compare other tank sizes, travel- and fill-speeds, or boom widths.
Productivity of a 3000 gallon tank pull-type (left) vs a 1200 gallon self-propelled (right), given specific speed, boom width, and fill times.
The specific design features of a sprayer may create additional productivity. For example, the ease of tank rinsing and cleanout can save time. European sprayers typically have lower remaining volume values, which increases the speed of tank rinsing and can eliminate the need for dumping tank remainders on the ground. Ease of filter inspection may seem trivial, but it permits more frequent confirmation that the system is clean and thus avoids potential future problems. An on-board pressure washer on the Amazone makes boom hygiene easier. It’s important to account for all these seemingly small gains because they add up.
Service
The success of any agricultural equipment relies on the equipment durability, fast availability of parts and service. Any new market entry will need to establish a dealer network, parts distribution system and superior service. This is no easy feat in a time of dealer consolidation. But without a drive train, there’s less to go wrong in a pull-type, and many plumbing parts are generic or can be obtained in metric equivalents.
With fewer mechanical components, pull-type sprayers require less service and are less prone to breakdowns.
Cost and Value
Prices vary, but a pull-type sprayer will usually cost less than half of a similar-sized self-propelled sprayer depending on the options selected.
With European-influenced equipment, the plumbing system will be more sophisticated, often offering recirculating booms, steering axles that follow in the tracks of the sprayer, narrow transport widths for greater road safety, an improved boom suspensions and levelling performance. It is safe to say that in terms of features, these sophisticated machines offer good value and many good design ideas. Operating costs are almost certainly lower, with better fuel economy and less drivetrain trouble.
The pull-type sprayer continues to have an important place to fill on our farms. With trade and weather anomalies lowering farm income, farmers are wary of being over-capitalized. It is conceivable that lower-cost and feature-rich alternatives to self-propelled units will have a fit. They certainly make sense on smaller farms that may not be able to utilize the full performance of a self-propelled, or on a larger farm that needs extra capacity but doesn’t want to bear the capital cost of a second expensive sprayer. The inherently slower working speeds allow for lower booms, less drift, overall improved deposit accuracy and uniformity. They’re worth a closer look.
How much horsepower (HP) do you need (really) when pairing a tractor and a towed sprayer or any other PTO powered implement? This important question should be asked BEFORE purchasing any towed implement. Surprisingly, there’s not much guidance out there, so you might hear answers like:
Whatever my tractor has must be enough… whatever that happens to be.
What?
The right amount of HP is what I can afford. Erma, grab that milk can full of egg money…
MOAR! (Yes, we know how “more” is spelled, but memes are funny).
Skeletor knows horsepower
Rating Tractor Horsepower
If you thought there was only one way to rate the horsepower of a tractor, well, you’d be wrong. At its simplest, horsepower is:
(torque × engine revolutions) ÷ a constant
We’ll expand on this later. The rub comes in how you define each of these factors and where you measure the power. Let’s start with something simple like engine speed, which is expressed in Revolutions Per Minute or RPM’s.
Engine Speed
So, if horsepower is the result of torque times engine speed, what speed do the manufacturers plug into the formula? One of two values are used:
1. Power Take-Off (PTO) Engine Speed
This is the engine RPM’s that produce the rated operating speed on the PTO. When the PTO is engaged, the engine is directly and mechanically connected to the PTO shaft. Therefore, maintaining the engine at the rated PTO speed, typically between 1,500 and 2,300 RPM depending on if it’s gas, diesel, turbocharged or not, will keep the PTO spinning at a uniform 540 or 1,000 RPM (the two typical PTO speeds) regardless of the driving speed.
2. Maximum Engine Speed.
This is the engine’s maximum intermittent operating speed… just shy of destroying said engine. An engine rated using the maximum speed gives you a false sense of security, because to get that horsepower you’ll be burning a ton of diesel, over-speeding your PTO implement, and wearing your tractor out very, very quickly.You wouldn’t drive your car around town in low gear because you’d redline the engine. Why would you do it to your tractor?
In the speedometer/tachometer (above the steering wheel) on this beautiful old tractor, the first black bar is the PTO rated RPM. The second is PTO Max. Operating with the PTO engaged above PTO Max can be damaging to the implement and to the tractor, and dangerous for the operator.
Horsepower Basics
OK, now we are ready to dig in a little deeper into defining tractor horsepower. What does it mean if, for example, your tractor is rated at 65 HP? We’ll skip the history lesson on watching the output of horses over an average day and move to the modern definition. Horsepower from a rotating shaft (such as the output of an engine) is:
Horsepower = [Torque in foot-pounds × Engine speed in Revolutions Per Minute (RPM)] ÷ 5,252
Here is a typical tractor torque curve. Notice how after peak torque, RPM’s climb quickly but net HP doesn’t. Unless specified, we can assume this is Engine Horsepower, not PTO Horsepower. If the above Torque/HP curves were your tractor, the PTO speed would likely be 1,500-1,600 RPM. According to the graph that would equate to about 82 HP. Running the engine up by 40% (2,100 RPM which is the max speed in this case, gets you about 98 horsepower. That’s only a 20% improvement. Remember, this is engine horsepower, not PTO horsepower, so this may not all be available for you to use. Image from JD.
Total Versus PTO Horsepower
Perhaps our tractor’s 65 HP rating describes Engine Peak Horsepower. This is what the engine would produce on a test stand, and it likely uses the maximum engine speed. This rating is a bit disingenuous. Not only because you will probably operate it at rated PTO engine speed, but also because some power is lost to internal processes, like the power steering pump, automatic transmission pump, alternator, auxiliary hydraulics, et cetera. So peak engine horsepower isn’t usually a very useful number unless you are in marketing and like big numbers.
A more accurate and useful rating is the Power Take-Off (PTO) Horsepower. This is the amount of horsepower available to do work at the PTO shaft. This may be at the rated PTO engine speed or the PTO Maximum speed. Estimating power using either speed offers a much more realistic rating of what you have to work with. As previously noted, PTO Rated Speed is usually near the speed where the engine creates the highest torque per revolution. This is often called the Power Band. Operation in this engine speed range will use the least diesel and result in the greatest amount of life in the machine.
Another important thing about PTO Horsepower is that this is the total amount of power available to do work. This could all go to PTO when the tractor is standing still, but both locomotion and the horsepower required to run the implement need to be subtracted from this number. So if your tractor is indeed 65 PTO horsepower, that’s the actual amount of horsepower you likely have to work with in real life.
In this excerpt from a Kubota Spec sheet, you see that the Rated Engine horsepower is quite a bit higher than the PTO horsepower. A 72 HP “rated” tractor really has 61 horsepower for you to work with. The 106 horsepower version on the right really has 91 PTO horsepower.
The Horsepower that Matters
To sum things up, PTO Horsepower is the number you really need to care about. All this up to now just to describe the nuances of how horsepower is expressed. No wonder HP is a topic that’s avoided. If you can find or download the manual, now you at least have the tools to get to how much horsepower you have to work with.
Maximum Load
In order to answer the question of how much HP you need, you must consider your operation. You need to size your tractor for the biggest load it will ever be used for, even if you only do that thing once a year. Typically this would be a sprayer, rotavator or a brush flail. The rest of the year you won’t burn much extra diesel if you aren’t using the power in a bigger tractor, but you can’t draw on horsepower that isn’t there in a smaller one.
Though it’s not common, you can have too big a tractor. You need only watch “Clarkson’s Farm” for ample evidence (and a chuckle).
The enormous and infamous Lamborghini tractor that starred in “Clarkson’s Farm” on Amazon Prime is a good example of taking horsepower a little too far.
The Basics of Estimating Load
Now that you have the extremes in mind, let’s get to scratchin’. There are three things you must know to determine the maximum load:
Locomotion – The power needed to move the tractor and implement
Implement Power – The power needed to operate the implement
Safety Factor – This is a buffer that gives us a little extra just in case.
For the following guesstimates let’s assume you are doing orchard and vineyard work with a compact/narrow tractor. There really aren’t any hard and fast equations for this, but these will get you in the ballpark. If you are a nut grower with full sized tractors or a vegetable/field crop grower, you may need to scale up.
Locomotion
People discount it, but the power required just to move the tractor and the implement around is substantial. If the implement is a fixed tower sprayer with a 500 gallon tank, this might require 15-20 HP on flat, dry land. If your topography includes hills, or your terrain includes mud or tall grass, you may need to double that requirement. 45 HP just to move around before you even engage the PTO. Speed matters, too; If you are driving 5 mph, you’ll need twice the HP versus driving 2.5 mph.
The manufacturer of the implement should be able to tell you how much horsepower the implement requires. Small, three-point hitch airblast sprayers may only require 10-15 PTO HP. Larger tower sprayers may require 40-50 PTO HP. Brush flails may take 25-45 HP.
This is where things can get sticky and you need to make sure you’re both talking the same language. Some manufacturers will tell you how much power the implement takes, others will skip all the steps in this article and go right to recommending the size tractor they think you’ll need. If you’re unsure, ask. Be sure to factor in the locomotion requirements discussed earlier, the dealer may not understand your conditions in their general recommendation but usually can provide some clarity with a little more information from you.
Safety Factor
It’s always a bad idea to run at 100% of your power capability. Most of you reading this article are likely working with mid-life or older tractors with a few thousand hours on them. Ol’ Bessie loses some of the pep in her step over time. After engine break-in, the tractor will slowly lose power capability over its life. The harder you work it, the faster this occurs. Enthalpy happens (now that’s a great tee-shirt idea). Plan for it. Once you have an idea of your worst-case locomotion and implement power needs, add them up and give yourself another 15% (That is, multiply by 1.15).
Summing It Up
Now we can finally answer the question. In order to determine how much tractor horsepower you need, follow these steps:
Understand the real PTO horsepower of the tractor you are considering. This is the only thing that matters. You should be able to find online documentation for this if it doesn’t come with the tractor or you’ve filed it somewhere that you’ll never forget…
Establish the maximum load you are likely to encounter. Calculate this by multiplying the sum of Locomotion and Implement Power requirements by a 1.15 Safety Factor.
If you are still unsure, discuss these factors with your trusted local tractor dealer, ensuring you are both speaking the same language. It is better to err on too much tractor than not enough, but do so within reason.
Looking at our original orchard application with a 500 gallon tank and a larger tower type sprayer, travelling around 3 mph:
35 HP for locomotion, 40 HP to run the sprayer and 15% safety puts us at 35 + 40 + [0.15 × (35+40)] = 86.25 PTO HP
Wishing you all MOAR POWER and perfect spraying weather.
Site-specific treatments have long been a goal in agriculture. It makes sense to provide inputs or treatments at rates that reflect the local situation. And to a large degree, those capabilities have been available for fertility and seed inputs for some time, with input zones reflecting soil types or topography.
Typical prescription map for nutrients (Source: Field Crop News)
But the
sprayer world has not seen as much site-specific treatment. One reason is that
pest maps are time-consuming to generate and their usefulness may be
short-lived. Or perhaps weeds are fairly ubiquitous, and it usually makes sense
to treat an entire field. Another reason could be that sprays are relatively
inexpensive compared to fertilizer or seed.
For
spraying, we need to re-define site-specific.
While
traditional zone maps (corresponding to, say soil type and/or elevation or
slope position) allow unique treatments on a scale of acres, new sensors have
allowed sprayers to basically leapfrog this approach and treat each square foot
uniquely. These sensors identify plants directly and create an immediate
treatment response.
Optical Spot Spray(OSS) principle (adapted from WEEDit)
The idea, and technology, has and been around agriculture since the early 1990s, with the Concord DetectSpray and later the Trimble WeedSeeker. For various reasons, these two never became widespread in North America, although a significant market formed in Australia and New Zealand. New cutting edge technologies are about to change this.
Green on Brown
Two main manufacturers have occupied the traditional Green on Brown Optical Spot Spraying (OSS) space, the Trimble WeedSeeker and WEEDit. Both have been available for over 10 years and are well established and proven reliable. WeedSeeker uses the Normalized Difference Vegetation Index (NDVI) principle to detect green on a non-green background. It employs one sensor per nozzle and the nozzle is either on-or off based on what the sensor detects. The WEEDit system is manufactured in the Netherlands by Rometron (https://www.weed-it.com/), and is widely adopted for use in Australia and South America. It is now making inroads into North America. The most recent version is named Quadro.
WEEDit spray booms contain sensors placed at 1 m intervals. These scan the ground ahead of the boom, identify the presence of plants, and trigger the nozzle in line with the plant. The newest Quadro sensor contains four channels so that its resolution is actually 25 cm (10″) wide. The boom therefore contains a nozzle every 25 cm, and this nozzle has a correspondingly narrow fan angle that treats just this space.
Hypro even spray (banding) nozzle with 30 degree fan angle. 30 and 40 degree nozzles are currently installed on WEEDit on 10″ spacing. 30 degree fan achieves approximately 8″ to 10″ band at target height. Boom stability is important
The detection principle is based on the quality of light that is reflected from living plant tissue compared to everything else. A red (older generation) or blue (newest generation, Quadro) light is emitted, and chlorophyll-containing plants reflect a unique wavelength that differentiates them from ground or dead plant material.
Older generation WEEDit sensors were placed at 1 m intervals and had five channels, each covering a 20 cm band. There were 180 nozzles on a 36 m (120′) boom.
The
response time of the system is very fast. Triggered by small solenoids, a
sprayer travel speed of up to 15 mph is possible when the sensor looks 1 m
ahead. Furthermore, the software allows the user two important controls: first,
the sprayed distance before and after a detected plant can be buffered between
5 and 20 cm, resulting in a sprayed patch between 10 and 40 cm long. This could
be useful when boom heights fluctuate and placement of the sprayed patch shifts
accordingly. Second, the user can select from among four sensitivity settings.
Higher sensitivity can detect smaller weeds but will also result in more false
results.
WEEDit Quadro sensor
One
reason the system has been successful in the southern hemisphere is the long
growing season that may require multiple spray passes outside of the crop each
year, and in which the weeds are relatively large at treatment time and
therefore easier to detect.
Water sensitive paper can be used to show whether a target has been detected (and therefore sprayed).
In North
America, the pre-seed spray window is relatively narrow and weeds may be very
small or just be emerging. The risk of a miss due to non-detection is therefore
greater. Fortunately, the WEEDit system has a feature that addresses this risk.
PWM valve for WEEDit, capable of instantaneous response at 10 to 50 Hz
The solenoids that trigger an individual nozzle are pulse-width modulated (PWM). This means that the application rate is adjusted according to travel speed via a duty cycle. And it offers an innovative capability: The entire boom can be programmed to spray a defined fraction of the full dose, to a maximum of 50%, as a background broadcast rate (called “Dual Mode” or “Bias”). The smallest weeds that escape detection are likely to be susceptible to this lower dose. Larger weeds are then detected and sprayed with an individual spot spray at the full dose. Dual Mode is typically set to about 25%; overall savings are less, but control is improved for those very early season situations.
A WEEDit Quadro boom can also be operated in “Cover Mode” for broadcast spraying where it functions as a full PWM system with turn compensation.
Currently, several hundred WEEDit sprayers are operating in Australia, and they’ve been available in Canada and the US since 2017. in 2019, Croplands, an Australian sprayer manufacturer owned by Nufarm, started representing WEEDit in Canada. It is available as a retrofit on existing booms, and can be ordered with a WEEDit Millennium aluminum boom that contains mounting brackets and wiring harness channels. Savings compared to broadcast spraying range from 65 to 85%.
In early 2021, John Deere announced its entry into the Green on Brown space with See & Spray Select™. This system is built around the ExactApply nozzle body and uses RGB cameras to differentiate green plants from non-green background colours. It will be in fields in 2022 according to John Deere. Similar RGB-based systems are in development by other manufacturers. Although their performance has not been compared side by side with WEEDit or WeedSeeker, initial specs suggest that the RGB systems are slower and are less able to detect small plants. Nonetheless, the future looks very promising.
In 2021, Hardi Australia announced a new product, called GeoSelect. This system does not have boom-mounted sensors, and instead sprays according to a prescription map developed by a drone. The advantage of this system is that the amount of herbicide needed is known in advance of spraying, and the knowledge of weed distribution in the field can allow for a more efficient coverage plan to be used. This system allows for spraying under any light condition, and adjusts for boom sway to ensure accurate placement. Drone map development is the responsibility of the applicator.
Green on Green
Green on Green spraying, which detects weeds within a crop and differentiates them from that crop, is advancing and the earliest commercial releases are now available in Australia, offered by a partnership between Bilberry and Agrifac (WeedSmart podcast here), as well as Bilberry and Goldacres with Swarmfarm. Others, notably the SmartSprayer from Amazone in partnership with Xarvio and Bosch and Greeneye Technology are entering field testing with commercial sized units in 2021 and 2022, respectively.
Opportunities for Optical Spot Spraying
Taken as a whole, optical spot spraying offers a number of opportunities for weed management.
Cost
Savings: OSS has
an appealing rate of return on investment. On a 5000 acre farm, a pre-seed
treatment of glyphosate plus tank mix for resistance management may cost
$10/acre, or $50,000 per year. At an average savings of 75%, that represents
$37,500 per year. Add other non-crop uses, such as post-harvest, and savings
increase. With eventual weed recognition in-crop, virtually all herbicide
treatments are candidates for such savings.
Herbicide
Resistance Management: Delaying the onset of herbicide resistance requires the use of multiple
effective modes of action in a tank mix. Cost is a deterrent to this practice.
With OSS, these tank mixes become affordable.
Efficiency: With 75% product savings, a tank
of product will last longer. The time lost to hauling water and product, as
well as filling the sprayer, will decrease. For example, WEEDit users are
spraying a full day on a single load. Or they may choose to use a much smaller
load, decreasing equipment weight.
Pre- and
Post-Harvest: Whether
for desiccation or weed control, site-specificity of late season sprays can
also be based on living tissue. Only regions in the field requiring the
desiccant are treated. Perennial or late-season weeds are selectively
controlled pre-harvest. Since herbicide rates in these applications are
typically higher, savings are significant.
High
value crops: Row
crops requiring multiple fungicide applications per season, such as potatoes,
can benefit from OSS. Sprays applied prior to canopy closure can thus avoid
gaps between plants, saving product.
Producer Innovation: One user of the WEEDit system in Saskatchewan developed an innovative use. Having missed a pre-seed spray, the applicator was faced with large weeds in a 1-leaf RoundupReady canola crop. By turning down the sensitivity of the system so the canola crop did not trigger the sensors and turning on Dual Mode, he was able to broadcast spray the field at a low glyphosate dose (sufficient to control the small weeds) and then apply a full dose to the larger weeds, triggered by the sensor.
Equipment Innovation: Since individual zones or weeds require unique doses or products, technologies like direct injection, remote nozzle switching, multiple smaller tanks and booms, and PWM will make more sense and grow. But the whole concept of detection and treatment can be moved away from pesticides to mechanical control or other techniques such as lasers, as does Carbon Robotics.
License
to Farm: OSS
makes intuitive sense not only to applicators, but also to the public at large.
Showing and using these technologies demonstrates stewardship practices that
are easy to communicate and understand.
Artificial Intelligence Scouting
Another approach is pioneered by several companies, for example Dronewerkers in the Netherlands (https://www.dronewerkers.nl/english/) Taranis (http://www.taranis.ag/), and Xarvio (https://www.xarvio.com). These companies have developed plant recognition algorithms that are currently able to identify over 100 different species. Each species can be divided into several growth stages. Taranis has launched a business in North America that scouts fields by high-resolution drone imagery, and then provides customers with maps that highlight potential agronomic issues such as weeds, disease, or insect damage.
Example of information available from artificial intelligence scouting. In this case, plant and foreign material information by species, relative abundance, and growth stage.
Resolution of the output can be species-specific (lambsquarters vs redroot pigweed), or by coarser resolution (broadleaf vs grass). The resulting output then shows the plant density at each location.
Weeds in a soybean crop (courtesy of Taranis)
Xarvio Scouting is a product in their Field Manager line (https://www.xarvio.com/en-CA/Scouting). App-based, the agronomist or producer takes pictures of their crops and the app is able to recognize weeds, diseases, insect feeding damage, as well as nitrogen status. The app is aware of other users in the area and basically crowd-sources emerging agronomic issues as they arise, communicating them back to the user.
The Xarvio Scouting app can identify certain weeds, diseases, and insect feeding damage from pictures taken while scouting (Screenshot from Xarvio.com).
The agronomic value of this information is clearly very high. Imagine knowing the distribution of weeds by species before and after treatment. Although we can already assess this when we walk fields, by conducting the task via drone we are measuring on a wide scale, permitting an accurate quantification of the treatment effect so its value can be assessed. This level of measurement intensity was not possible before. Yield loss models for time of removal of certain weeds at certain growth stages can be applied across the entire field, and economic analyses allows follow-up treatments to be tailored to specific portions of the field.
Green-Eye Technology artificial intelligence can differentiate these ragweed plants from the pea crop. (Courtesy Green Eye Technology).
Or
imagine following specific patches of weeds over time, to monitor the
effectiveness of a certain cultural practice, or be alerted to the
establishment of a resistant population while it’s still feasible to contain
it.
Heat maps can be generated to document weed patches, and perhaps monitor their size over time. (Courtesy Green Eye Technology).
When this information is converted to a prescription map, rate and tank mix composition (or cultural controls) could be varied as necessary by zone, or weeds could, in the future, be sprayed individually. Perhaps future autonomous robots could be deployed more efficiently.
Identification of plant symptoms in canola (Courtesy of Taranis)
Development and improvement of these technologies is ongoing rapidly. Finally, we may have all the pieces that can bring site specific weed, disease, and insect management to market.
Small-plot agricultural sprayers should have a pressure gauge on the wand or boom to ensure accurate application rates. Most are added after-market and the operator has the choice of buying liquid-filled or dry gauges.
Glycerine- or silicone-filled gauges are preferred because
they dampen pressure spikes, pulsation and mechanical vibration. Compared to
dry gauges, they are available in higher ranges and are less prone to moisture
problems (which cause corrosion, accuracy and visibility issues).
We use 100 psi (~7 bar) liquid-filled gauges for our handheld
sprayers. Only recently did we acknowledge the sticker affixed to the glass advising
the user to cut the nipple off the rubber plug located at the top. Preferring
to avoid messy leaks, we have always left it intact.
We wondered what impact, if any, this was having…
What are Vents?
Expensive gauges have mechanical vents that can be opened prior to use and closed to retain liquid when stored. More commonly, there is a rubber plug with a protrusion (referred to as a nipple).
Why Vent?
Mechanical, liquid-filled gauges are sealed to keep the
liquid in. When there are temperature fluctuations, the liquid expands or
contracts and creates “case pressure”. This exerts a force that interferes with
the pressure reading.
According to Marshall Instruments, case pressure can offset the accuracy by approximately 1 psi (0.07 bar) for every 35˚F (20˚C) temperature change, but is only noticeable when measuring lower pressures (0-15 psi or 0-1 bar). Nevertheless, they advise all gauges should be vented prior to use.
The plug can be removed to allow the user to refill the gauge, maintaining an air space of about ½” at the top of the window. If the nipple is cut off, the gauge is permanently vented and will leak if the gauge is not kept vertical.
Testing
We performed an experiment to see if typical working temperatures had a practical impact on the accuracy of an unvented gauge. We suspended an unvented, liquid-filled gauge upright in a water bath at approximately 15˚C, 30˚C or 45˚C (59˚F, 83˚F or 113˚F) until it equilibrated. The high temperature may seem unreasonable, but gauges left in trucks on summer days get far hotter.
The gauge was quickly removed and placed in a manometer
(Ametek T-975) where it was subjected to pressures of 15, 30 and 45 psi (1 bar,
2 bar and 3.1 bar) and readings recorded. This was repeated five times. We then
vented the gauge and repeated the process.
Results
At first, there appeared to be very little difference in average accuracy of vented and unvented gauges. Accuracy refers to the closeness of a measured value to a standard or known value. Perhaps there was some small increase in the pressure reported by an unvented gauge, but very little practical difference.
However, when we look at variability we get a different picture. Variability is a measure of precision, which refers to the closeness of measurements to one another. The graphs show that an unvented gauge has greater variability (less precision) at lower temperatures and lower pressures.
A good way to think of accuracy and precision is using the classic archery bulls-eye metaphor. The unvented pressure gauge is best represented by the third image, where it is accurate (on average) but not precise (variable).
Real-World Example
What does this mean in practice? Consider someone spraying a small plot using a TeeJet XR8002 nozzle on a CO2-powered hand boom at 30 psi. The difference in output between 30 psi and 40 psi is about 0.003 gpm / psi.
An unvented pressure gauge used on a hot day may read 1.5 psi lower, causing you to overcompensate and raise the pressure 1.5 psi higher than intended. That would result in 0.0045 gpm (0.5%) more applied. Compensating for an unvented gauge on a colder day might be closer to 0.009 gpm (1%) more applied.
Assuming a walking speed of 3.1 mph (5 km/h) and a swath of 20” (50 cm), the nozzle should emit about16.3 gpa at 30 psi. Unvented in the heat, that’s 16.7 gpa. At 33 psi, that’s 17.15 gpa. That’s almost 1 gpa more than intended. Potentially, the lack of precision could make a significant difference.
Conclusion
Liquid-filled gauges are preferred over dry gauges.
To ensure precision, the gauge should be vented prior to use.
Permanent venting on a hand-held sprayer causes leaks, which is a nuisance, so we suggest simply lifting the edge of the plug with a screwdriver or fingernail to vent the gauge prior to each use.
This work was performed by OMAFRA summer student, Aidan Morgan.
Enjoy our take on a Dr. Seuss work-of-art. We’re sure the fine doctor would want to end resistant pig weed’s reign of terror as much as we do. Hear us recite it in the sound bar, read it yourself, or head to the bottom of the article to see the talented Bridgette Readel (@bmreadel) read it for you. Enjoy!
Press Play to hear the audio version of this article
In the home farm’s west field, where the soybeans won’t grow, and the wind blows the soil from deep tillage you know, and no pollinators come, excepting old crows is the patch of resistant pigweed.
And downhill in the boundary, some neighbours say, if you look close enough you can still see today, where herbicide persisted, in the places it drifted, from the winds that took it away.
How did it drift? How did it get there? And why was it lifted and taken somewhere from the home farm’s west field where the soybeans won’t grow? Look to the sprayer. Look close, and you’ll know.
You won’t see Coarse nozzles. You will see high booms that wobble and bounce on a sprayer that zooms in headwinds too high in the late afternoon. They may even spray by the light of the moon!
Check the chemical shed. Crack the door, just a fraction. You’re likely to see A lone mode of action.
“Tell me how,” says the farmer “I’ll do what you say.” “But I only have so many hours in the day to spray the west field where the soybeans won’t grow, and battle the pigweed that simply won’t go.”
“Oh the things you can do! So much can be done!” “Learn to spray in light winds, in the day, in the sun!” “Lower booms, use more water, use droplets so Coarse.” “We’ve told you before… (you will note we are hoarse.)”
The farmer said nothing, just gave us a glance. We could tell he was thinking of time, effort and cash. “Driving slow improves coverage, and you can make up the time, with faster fills, longer booms, and more precise A-B lines.”
That was long, long ago. Let’s check in today, and see if the problems have withered away.
In the home farm’s west field, where the soybeans now grow, and cover crops cling to the soil down below, the pollinators buzz because drift doesn’t blow.
