Tag: wheat

  • Characterizing RPAS Coverage at Four Cardinal Points on a Vertical Plane: Practical implications for spraying wheat at T3

    Characterizing RPAS Coverage at Four Cardinal Points on a Vertical Plane: Practical implications for spraying wheat at T3

    Global research into Remotely Piloted Aerial Systems (RPAS) is producing pesticide residue, drift and efficacy data that is helping to inform federal regulatory policy. It is reasonable to assume that Canada will ultimately sanction the use of RPAS for agricultural spraying. The first registered products will likely be fungicides intended for broad acre crops such as soybean, corn, and wheat.

    Those considering RPAS for agricultural spraying have expressed interest ranging from general curiosity to high demand. Successful adoption will be contingent on expectation management, which in turn requires education on the functional differences between RPAS and conventional application technologies.

    Quadrotor RPAS design dominates the current commercial landscape, with typical models featuring four rotary atomizers and 40 L tanks. There have been improvements in recent years, but these designs continue to suffer from a low rate of productivity (by North American standards for broad acre crops). This is due, in part, to low volumetric capacity and limitations with rotary atomizer design, which result in a debatably short effective swath width. Broadly, “swath width” refers to the minimal span consistently sprayed by a single pass, while “effective” indicates a spray coverage (i.e. deposition pattern and threshold dose) sufficient to achieve the desired result.

    Our research efforts have focused on identifying and evaluating variables that influence effective swath width. These include operational settings such as altitude, travel speed, volume applied and nozzle settings. They also include environmental factors such as meteorological conditions, crop morphology, and planting architecture. Establishing a combination of settings that account for these factors will inform operator practices and optimize the balance between RPAS effectiveness and efficiency.

    Study Objective

    Fusarium head blight is a significant economic threat in wheat. Fungicide application takes place at the T3 stage of development, with the intention of providing panoramic coverage of the wheat head. RPAS is being considered to apply these fungicides.

    The pursuit of productivity tempts operators to push operational settings to the point that spray coverage is compromised. This study will use operational settings based on the results of previous work and assign flight speed as the independent variable.

    Coverage will be assessed using water sensitive paper (WSP) positioned at the top of the canopy and oriented vertically in four cardinal directions to emulate the circumference of the wheat head. Isolating the resultant coverage in each cardinal direction may provide insight into droplet behaviour within the RPAS spray cloud and perhaps better assess effective swath width.

    Coverage from a conventional field sprayer will also be characterized. This represents the current standard and it will provide a basis for comparison.

    Materials and Methods

    Site

    The experiment was conducted at 45939 John Wise Line, St Thomas, Ontario (42.7320746, -81.0879887) on June 1, 2025. Common seed wheat was planted on October 6th, 2024, at 1.8 million seeds/ac on a 19 cm (7.5 in) row spacing. At the time of spraying, wheat was at the T3 stage of development, approximately 0.7 m (2.5 ft) high.

    Holder Design

    3D-printed holders were designed in Autodesk Fusion. They feature tabs that create a pressure fit (for quick WSP loading and unloading) and a back support (to prevent WSP movement in a downwash) to vertically position 1×3” WSP facing out on four cardinal points (figure 1). 21 poles were positioned on a 1 m spacing, leaving the tops coplanar with the wheat heads for in situ swathing. The square cross-section of the poles corresponded to a square depression in the WSP holder, ensuring the samplers were correctly aligned (figure 2). The gcode file to 3D print your own holders can be downloaded here. We used PLA filament with 3 walls and a 15% rectilinear infill to print 16 holders at a time on a Bambu P1S.

    Figure 1. 3D-printed WSP holder slotted onto a pole in the wheat field.
    Figure 2. Four WSP positioned vertically, facing four cardinal points, at wheat-head depth.

    Wind direction is indicated by the direction the wind is coming from, not the direction it’s blowing to. Therefore, a wind blowing in a northern direction is referred to as a southern wind. The WSP holders were aligned east to west, perpendicular to the prevailing southern wind. We established a trampled path ~0.75 m on the downwind side. This left the wheat canopy surrounding the samplers intact while still permitting access to the WSP holders (figure 3).

    Figure 3. 21 WSP holders on 1 m spacing with access ~0.75 away.

    WSP were given unique serial numbers to identify their position, and pre-loaded into the holders. 170 loaded holders were stored on raised grids inside four shallow plastic bins, arranged in the order they would be used (figure 4). This greatly expedited placement and retrieval, allowing for more repetitions to take place while optimal weather conditions held.

    Figure 4. WSP holders arranged in sequence in a storage bin. This allowed the pre-loading of serial numbered WSP prior to the day of the experiment.

    Application Method

    A DJI Agras T50 RPAS maintained and calibrated by the cooperator was fitted with four rotary atomizers. Previous work has demonstrated that higher rates of flow can have a detrimental effect on the spray quality from rotary atomizers, so distributing the flow over four nozzles was intended to prevent this. The atomizers applied a 250 µm spray over a 7 m swath width (corresponding with route spacing), as selected on the flight controller. Altitude was 3 m above the wheat heads, and flight speed was either 6 or 10 m/s (three repetitions each). Application volume was 50 L/ha, anticipating this to be a future label requirement.

    The RPAS flew a racetrack pattern over the samplers (figure 5). It flew with a prevailing tailwind between samplers 14 and 15, and then back with a prevailing headwind between samplers 7 and 8. We employed a DJI RTK-1 base station, which claims 1 cm horizontal accuracy.

    Figure 5. Racetrack flight path relative to WSP holders and prevailing wind direction.

    The RPAS was given sufficient distance (~40 m before and after the samplers) to reach the target speed, which was confirmed with a screenshot from the flight controller. The RPAS tank (capacity 40 L) contained municipal water with 0.125% v/v of NIS (Ag-Surf II). The level of liquid in the RPAS tank was maintained at 40 L throughout the trial to eliminate the effect of a changing payload.

    The field sprayer, maintained and calibrated by the cooperator, was a New Holland SP 275s. It extended the left boom over the samplers from position 1 through to 12 and made a single pass with a prevailing tailwind (three repetitions). It traveled at 4.5 m/s (16 km/h or 10 mph) spraying 187 L/ha (20 gpa) and rough terrain caused the boom height to fluctuate between ~25 cm and ~50 cm above the wheat heads. The nozzles were Greenleaf Technologies TADF 06 (greys) on a 50 cm spacing operated at 50 psi to produce a Coarse spray quality. The tank contained municipal water with 0.125% v/v of NIS (Ag-Surf II).

    Trial Procedure

    WSP holders were placed just prior to spraying while the RPAS or field sprayer was positioned ~40 m beyond the samplers. When wind conditions were deemed appropriate, a signal was given to initiate spraying. On pass completion, one minute elapsed before initiating collection to permit complete deposition of the spray and drying of the droplets.

    Weather Data

    Weather data was collected using a Kestrel 3550AG weather meter (Kestrel Instruments) in a vane mount positioned roughly 1 m below RPAS altitude. Data was logged as the RPAS or field sprayer boom passed the samplers (table 1). In the case of the RPAS, there was very little difference between the two passes per repetition, so values were averaged.

    TimeRep and TreatmentTemperature (°C)Wind Speed (km/h)Wind Direction
    10:21:511. RPAS 6 m/s16.43.1S
    10:33:562. RPAS 6 m/s17.76.2S x SW
    10:45:503. RPAS 6 m/s18.84.0S x SW
    10:55:401. RPAS 10 m/s18.62.1SW
    11:06:242. RPAS 10 m/s20.00.5S
    11:16:003. RPAS 10 m/s19.25.8S x SW
    11:29:541. Field Sprayer21.10.0S
    11:41:122. Field Sprayer19.91.7S x SW
    11:48:313. Field Sprayer20.23.9S
    Table 1. Time and weather conditions for each repetition. Data was captured as the nozzles passed over the holders. Wind direction is indicated by the direction it is coming from.

    Digitization

    WSP (Spot-On) were scanned using a DropScopeTM (SprayX). The software reported droplet density and percent area coverage, but only deposit density is considered in this report.

    Results

    Comprehensive Observations

    When the average deposit density from each of the four WSP per holder is added, we have a measure of total panoramic coverage. The mean total panoramic coverage from three repetitions of each treatment is shown in figure 6. For the RPAS treatments, distinct coverage peaks typical of RPAS applications correspond to the flight passes through poles 14-15 and 7-8. There is a slight spray displacement due to an occasional shift to a west wind (i.e. overall coverage shifted towards pole 1). However, the entire spray swath appears to have fallen within the range of the samplers. The back-and-forth flight pattern produced higher coverage at the interface between passes (pole 10) compared the extremes (beyond poles 19 and 3) suggesting some overlap. Deposit density was higher for the slower RPAS flight speed, and RPAS produced a higher deposit density than the field sprayer. Field sprayer coverage data is included for perspective but is generally not referred to unless it has some bearing on the evaluation of the RPAS coverage.

    Figure 6. Mean sum deposit in count/cm2 for each treatment. RPAS 6 m/s deposited an average 700 drops/cm2. RPAS 10 m/s deposited an average 400 drops/cm2. The field sprayer deposited an average 280 drops/cm2. r=3. S.E. bars shown. Arrows indicate RPAS flight path and direction.

    Swath Width

    If the coverage at pole 10 represents the edge of each swath, then a swath width of ~6.0 m can be estimated based on similar coverage at poles 16-17 and 3-4. This is less than the programed value of 7.0 m.

    This inference is supported when these averaged values were entered in an Excel-based model that calculates swath width. The model sums deposits from adjacent swaths assuming a racetrack pattern. Threshold coverage is subjective but adhering to the objective of establishing a balance between over- and under-dosing with the lowest possible C.V., we calculated swaths between 5.0 and 6.5 m (table 2).

    TreatmentPole PositionThreshold Coverage (count/cm2)Under-dose (%)Over-dose (%)C.V. (%)Swath (m)
    RPAS 6 m/s21-1012010.45.018.05.5
    RPAS 6 m/s10-11205.714.126.05.0
    RPAS 10 m/s21-10809.111.425.46.0
    RPAS 10 m/s10-13517.214.143.46.5
    Table 2. Swath widths calculated from the average cumulative deposit density for each WSP holder.

    It was expected that the field sprayer would produce a somewhat trapezoidal coverage pattern, tapering up at pole 12 (boom extreme) and level to pole 1 (sprayer chassis). Instead, note the gradual increase in coverage from pole 12 to 1. This is likely the result of boom yaw, where the boom end rose higher than the point closest to the sprayer. If this degree of coverage represents the industry standard, it is notable that the average boom coverage is either on par with, or considerably less, than that of the RPAS.

    Deposit Density

    The RPAS was programmed to produce a 250 µm droplet size, while the field sprayer produced Coarse (~218-349 µm) droplets. Smaller stains were produced by the RPAS than the field sprayer (figures 7 and 8), and their circular/oval shape suggest both a smaller droplet volume and a somewhat perpendicular flight path. Droplets produced by the field sprayer left long streaks, which suggest higher droplet volumes and a more parallel flight path.

    Figure 7. Typical deposition pattern from a single WSP holder in the centre of the RPAS flight pattern. Considered from the perspective of the RPAS, WSP starting at the top and rotating clockwise are left side, retreat side, right side, and advance side.
    Figure 8. Typical deposition pattern from a single WSP holder nearer the field sprayer chassis. Considered from the perspective of the field sprayer, WSP starting at the top and rotating clockwise are left side, retreat side, right side, and advance side.

    When the overall average coverage is calculated the RPAS at 6 m/s deposited an average 700 drops/cm2 and an average 400 drops/cm2 at 10 m/s. The field sprayer deposited an average 280 drops/cm2. When volume remains constant, smaller droplet diameters produce a greater number of droplets than with larger droplet diameters, so more droplets would be expected from the RPAS. However, the RPAS applied only 50 L/ha while the field sprayer applied 182 L/ha. Therefore, the RPAS distributed a greater density of potentially higher-concentration droplets on each WSP holder compared to the field sprayer. Further, a slower flight speed deposited a higher density of stains than a faster flight speed.

    Effect of Travel Speed

    The 6 m/s treatment resulted in slightly smaller swath widths (1 m or 15% less) than the 10 m/s treatment. The positive relationship between swath width and flight speed has already been established. The positive relationship between flight speed and off target drift has also been established, which may account for the significantly fewer deposits (almost 50% fewer) in the swath at 10 m/s versus 6 m/s. When a higher deposit density is valued, such as in the case of contact fungicide application, the loss of productivity from a slightly smaller swath width is a reasonable compromise for the superior coverage within that swath.

    Coverage by Cardinal Point

    North Facing WSP

    This side of the WSP holder faced north, away from the prevailing south wind. The RPAS deposited far more on this face when traveling with the wind between poles 14-15, making this side face the RPAS retreat (figure 9). It suggests the RPAS blows down and back, even against a tail wind. This is supported when RPAS returned between poles 7-8 and deposited comparatively less on this face.

    Figure 9. Mean sum deposit in count/cm2 for each treatment on north facing WSP. r=3. S.E. bars shown. Arrows indicate RPAS flight path and direction.

    RPAS speed may have had an effect. With airblast sprayers, slower travel speeds produce greater dwell times, which increases the distance a droplet travels on a given trajectory. Logically, when flying away from the retreat face, higher speeds would impart a greater forward momentum on a droplet, cancelling out some of the backward momentum (watch a video here). If this were the case, there would be comparatively improved deposit density on the 14-15 pass for slower speeds and reduced coverage between poles 7-8 as it blew past the target. Figure 9 supports this hypothesis.

    South Facing WSP

    This side of the WSP holder faced south, into the prevailing south wind. Considering the 6 m/s treatment, we see more coverage on the 7-8 pass than the 14-15, because it represents the retreat side of the sprayer (figure 10). The differential is far less on this plane than the north facing (figure 9) because the prevailing wind likely blew spray into the WSP on the 14-15 pass. Nevertheless there is significantly more on 7-8.

    Figure 10. Mean sum deposit in count/cm2 for each treatment on south facing WSP. r=3. S.E. bars shown. Arrows indicate RPAS flight path and direction.

    This relationship is less clear for the faster 10 m/s treatment. There does tend to be higher deposit on the 14-15 pass as spray was blown into the collectors. However far more was expected on this face for the 7-8 pass as it represents both the retreat face and has the added benefit of wind. Further, there was far less coverage overall when compared to the slower flight speed. We have no explanation for the lack of coverage on the 7-8 pass and can only conclude that higher speeds left droplets airborne and were not conducive to coverage.

    West Facing WSP

    This side of the WSP holder faced west, into the slight west wind. We see coverage is almost exclusively on those WSP facing the drone (figure 11). In other words, as the RPAS passed between 14-15 and 7-8, coverage was positively skewed from this point. The skewed coverage was evident at both flight speeds, but overall coverage was higher for the slower speed. Once again, we cannot explain why there was significantly reduced coverage on the 10 m/s pass between poles 7-8 except to suggest the spray may have remained airborne.

    Figure 11. Mean sum deposit in count/cm2 for each treatment on west facing WSP. r=3. S.E. bars shown. Arrows indicate RPAS flight path and direction.

    East Facing WSP

    This side of the WSP holder faced east, away from a slight west wind. We see that coverage is almost exclusively on those WSP facing the drone in the upwind direction (figure 12). Overall coverage was slightly higher for the slower speed, but far less overall coverage compared to the west facing samplers (figure 11). This is likely because the light west wind caused spray to displace from pole 21 to pole 1, washing past the back (insensitive) sides of the WSP.

    Figure 12. Mean sum deposit in count/cm2 for each treatment on east facing WSP. r=3. S.E. bars shown. Arrows indicate RPAS flight path and direction.

    Summary

    RPAS can provide par or better panoramic wheat head coverage compared to a conventional ground rig when they are flown using reasonable operational settings in optimal environmental conditions. A moderate flight speed (~6-8 m/s), appropriate altitude (~3 m above wheat heads), and four rotary atomizers producing a Medium-Coarse (~250 um) droplet size can produce an in situ 6 m swath width at 50 L/ha. Higher flight speeds produce a marginally wider swath at the cost of reduced droplet density and increased drift potential.

    Assessing coverage using vertical WSP facing four cardinal points has provided further insight into the behaviour of spray from an RPAS. Droplets from any application technology tend to deposit with wind and gravity, but rotor downwash represents an additional variable unique to RPAS. That force, combined with a forward cant of the drone during flight, lead droplets to deposit on vertical surfaces that face the rear (retreat) of the sprayer as well as surfaces that face and intercept spray that radiates laterally from the flight path.

    Drone Spray Canada, Bayer Canada, volunteers Kurtis Pilkington and Natalie, and grower-cooperator Adam Pfeffer are gratefully acknowledged for their contributions to this study.

  • 28% UAN in Winter Wheat: Drive-Along Diaries #2

    28% UAN in Winter Wheat: Drive-Along Diaries #2

    I’d been pestering Dan Petker to let me come along as he and his father Paul applied 28% UAN to the winter wheat on their family farm in Port Rowan, Ontario.

    Me: “Today?”
    Dan: “Nope – Wheat’s not at the right stage.”
    Me: “Today?”
    Dan: “Nope – Rain in the forecast.”
    Me: “Today?”
    Dan: “We’ll see if the ground can hold a full sprayer. I’ll let you know.”

    April 26th, 8:00 am

    My first lesson was a reminder that farming requires a lot of advance planning and preparation because ultimately, it’s opportunistic. The Petkers were toeing the start line as they focused on weather forecasts, crop staging and field conditions. As soon as they determined that the wheat in the tram lines would bounce back rather than get mashed into the soil, they were ready to roll. I suppose I was opportunistic as well because as soon as I got the thumbs-up I dropped everything and raced to their farm.

    10:30 am

    When I arrived, I found Dan filling their tender wagon in the yard. All their farm inputs are stored in their chemical shed, including 27,000 gallons of 28% UAN. The wagon had two, 1,000 gallon tanks which Dan was filling from a 2” line. He said that as the season progressed, they would move up to faster fills by swapping to a 3” line. They weren’t in that kind of rush today and he didn’t want to have to lug the heavier line around if he didn’t need to. Fair enough. At that point Paul radioed from the sprayer to tell Dan he was ready for his first refill.

    As we drove to meet Paul, I learned that the goal was to spray two fields totaling 200 acres. A single, 1,000 gallon tankful would cover 20 acres. Dan noted that these soils were a loamy silt and clay mix that held nitrogen very well. On sandier soils, farmers often choose to split the application where a smaller amount is applied earlier in the season and the remainder later, but Dan said it never paid dividends on these fields. Of course, that reasoning may have been moot since it was such a wet spring; They couldn’t get out earlier even if they wanted to.

    The two fields were within a 5 km radius from the yard, so nothing was more than 10 minutes away. The county roads were narrow, but throughout they day I saw that the locals knew how to share the road with farm equipment; lots of polite waves and no one risked their necks trying to pass. Good to see.

    10:40 am

    We pulled up alongside the sprayer and Dan started filling as I greeted Paul, who’d I’d ride with for the rest of the day. We were using their John Deere R4038 equipped with Pentair Hypro six-stream fertilizer nozzles (FC-ESI-11015’s) on 15” centres. The Petkers used 06’s the year before and found they had to drive too slowly, so investing in these larger nozzles was a productivity booster.

    While filling, they both watched the sight gauge on the side of the sprayer. I asked why they didn’t use a flowmeter and they said it could be off by +/- 10 gallons, so if the sprayer was level, the sight gauge told them what they needed to know.

    10:50

    I joined Paul in the cab and we drove into the field. Paul pointed out the pink field boundary on the monitor and grimaced at the rounded corners that were established during planting. He wanted to reset the A-B lines and square off those corners. His reasoning was to ensure weeds didn’t grow in the margins and affect yield. However, he also said it looked terrible and I got the impression this was as much about pride in a job well done as it was yield.

    We backed into the corner. Paul explained that the rate controller “hunts” a little as the sprayer speeds up over the first few meters and wouldn’t apply a full or consistent rate. By temporarily disengaging it until we got up to speed, we would avoid the weed escapes common to field corners. We’d be applying a slightly higher rate than required for those first few meters, but it was the lesser of two evils.

    He set the first pass using GPS: “Got-Paul-Steering” and I watched as the breakaway section started snagging the treeline on the edge of the field. I asked if that was a problem and he replied that he was driving slowly, and it didn’t bother anything. It was important to get those margins and the trees were always growing and dropping branches, so hits were inevitable.

    Soon we were back in the hands of GPS-guided autosteer and rate control and moving at a respectable 12 mph. 20 acres later we’d sprayed the 1,000 gallons and were headed back to meet Dan for a refill. On the way we noticed a triangular area that we missed while I was distracting Paul with questions. He said we’d double back later and let sectional control take care of it. Paul loved sectional control.

    11:30

    Soon Dan was empty, and we were full, so we got right back at it. I wouldn’t describe the field as hilly, but it was far from flat. On occasions where the sprayer dipped significantly, one side of the boom would sometimes kiss the ground while the other hung precipitously in the air. We had the boom height set to about 36” but Paul was manually raising each side if the boom got too close. You can forget the fantasy of sitting back and letting the machine do all the work; It certainly wasn’t the case, here.

    Slower travel speed and a reasonably-low boom are the best practice for crop protection sprays. However, streamer nozzles don’t form droplets and overlap was maintained, so I wasn’t worried about our lively boom causing drift or coverage uniformity concerns. I was, however, increasingly focused on my lower back and teeth. The buddy-seat didn’t have the padding or air-ride suspension Paul was enjoying.

    When we hit level ground again, I began to appreciate the process of passing back and forth over a field. It was satisfying to watch the sprayer icon on the monitor filling the screen with blue as we covered ground. Like the old-school, low-res, 1980’s video games that ate all my hard-earned quarters. Then we were empty again and it was time to go beg for more quarters.

    11:46

    Dan was busy so we drove back to the yard rather than wait for tender. There was a Rogator on the road ahead of us and Paul pointed out the muck it was flinging from the tires. A quick peek behind us showed we weren’t tracking mud. Paul said it was because of their soil management practices – no-till left the fields better able to weather droughts and absorb rains. The Rogator was operating in fields that employed deep tillage and were full of standing water and now, muddy tire ruts. Paul pointed out a few such fields as we drove, and I could soon see for myself which fields were managed by the Petkers and which were not. In fact, I only saw one puddle of standing water in their fields that day when all around us were shallow swimming pools.

    12:15

    We filled, drove back to the field, and picked up where we left off. Paul noted they had to plant their wheat a little later than they would have liked because they were delayed getting the beans off. Despite that, he was very happy with the stand we were fertilizing. We were able to have this conversation because Paul (like Dan) did not listen to music or podcasts in the sprayer. He said it helped him focus and that he liked the peace. I think being alone with my thoughts all day would have driven me around the bend. And then we were empty again, so back to the yard.

    12:47

    We filled, drove back, engaged the A-B line, and started the last section of this field. I asked about sprayer sanitation. UAN is notoriously caustic and can cause compatibility issues with some products, so I wanted to know how diligent they were about rinsing or cleaning (two different things). Paul agreed that it was messy stuff and it got all over the sprayer. So, at the end of the day, they would perform a thorough rinse of the plumbing before washing the exterior out behind their equipment shop. We finished with 300 gallons left in the tank, so we elected to head over to the second field.

    1:10

    At field number two, Paul changed fields on the monitor and grumbled about the round corners on the boundary. He pointed out that the edge of this field wasn’t straight – it contoured along a wavy treeline. Paul briefly disengaged rate control, set the “A” point and started driving manually again, hugging the treeline and dipping in and out using Got-Paul-Steering until we’d cleared the trees. Now that the field boundary was straight, he erased the “A” point and set a new one before later setting the “B”. He looked over at me, anticipating my question, but I’d already guessed that Paul didn’t want to repeat that wavy line on every subsequent row. Instead, we’d now run parallel to a straight A-B line and let sectional control handle the overlaps on our twisty start. That earned me an approving smile. And to add to that feeling of pride, our tank emptied exactly at the end of that first row. Perfect.

    1:27

    Back at the yard for our refill, I thought about how long our previous fill times were compared to now. From this second field it was 10 minutes on the road, 10 minutes to fill, and 10 minutes back, so 30 minutes compared to maybe 15 for the first field. Longer than I thought it would be. At 1:48 we were back and spraying again and I was beginning to notice how technical this field was. We performed a number of three-point turns in order to back into corners while the monitor alternated between happy chirps and stern alarms as we passed over A-B lines. Then we were empty, so back we went for more.

    2:41

    To continue to video game metaphor, this field was an advanced level and the Big Boss was coming. Not only was the shape odd, but it had chain link fences, posts, more trees, a water course, and they stored some farm equipment on one part of it. Paul calmly negotiated all these obstacles with stops, starts, boom adjustments (either height changes or partial folds), and then, shockingly, asked me to drive.

    Paul: “Line up the tracks.”
    Me: “I’m trying.”
    Paul: “Do not try or you won’t get it right. Do!”
    Me: “…what!?”

    As a card-carrying Star Wars fan, I thought Paul was teasing me. His Yoda impression was perfect. I asked if he’d seen Star Wars and he replied that he was vaguely aware of it. So, he was being sincere, and I relaxed knowing I was in good hands. I even negotiated a few turns under his tutelage. But I confess I was relieved when the hydrostatic lightsaber was back in his capable hands.

    3:04

    Empty. Drive. Fill. Drive. Spray at 3:43. The last section was quick and easy and once we’d finished, we headed to their equipment shop to find Dan waiting. Dan pointed out the nitrogen all over the sprayer and reinforced Paul’s assertion that they’d rinse it out and wash the exterior off later that evening.

    He drove me back to the yard so I could retrieve my car and we said our goodbyes. As I was headed home, I happened to pass their equipment shop where I saw Paul, a man in his mid 70’s that hadn’t stopped to eat and had been spraying all day, hard at it washing off the exterior. Wow.

    Take Homes

    I’m guilty of over-emphasizing the fill-time aspect of spraying because that’s the biggest time-suck on productivity. However, some tank mixes (e.g. SC’s) don’t appreciate being rushed, and while time is always pressing, there are those occasions where it isn’t mission-critical. Fill-time never came up on this job. There were, however, other aspects that deserved attention.

    In the case of applying UAN to winter wheat on these irregularly shaped home-farm fields, it was more important to be attentive and manually adjust sprayer settings to fit the moment rather than always trust in the technology. Granted, the technology (namely rate control, boom leveling and GPS sectional control) was brilliant once we’d finished the headlands and dealt with any obstacles and topographical challenges.

    I also appreciated that this family has been farming for many years. Dan and his father had a practiced rhythm that made it look easier than it actually was. Equipment was prepared, decisions were made, and everything was in place well ahead of the application. That included how they managed their soil and knowing how their fields responded to nitrogen. They communicated well, using digital records and redundant written notes to ensure everything was coordinated and going to plan, and that good planning made for a good day.

    And it was a good day.

  • Nitrogen Application Technology in Winter Wheat

    Nitrogen Application Technology in Winter Wheat

    With an ever growing selection of options for nozzles and streamer bars, many growers are asking the question, what should I outfit my sprayer with for winter wheat liquid fertilizer applications? Well, it depends on what are you trying to accomplish.

    If the goal is to push your winter wheat management and improve yields, then the accurate and uniform application of liquid nitrogen is key. Selecting the appropriate sprayer technology can have a huge impact. Using a twitter poll, we learned that growers use many methods:

    • 3, 5, 6 or 7 hole streamer nozzles
    • Flood nozzles
    • 3 or 5 hole streamer bars

    Let’s look at some of the options and consider why you might choose one technology over another.

    Floods on a Terra-Gator. Photo courtesy of Kyle DeCorte.

    Air Induction, Conventional Flat Fan or Flood Nozzles

    Let’s get this one out of the way first. Air induction (AI), conventional flat fan and flood nozzles are a no-go when it comes to applying 28% UAN in winter wheat. Dr. Peter Sikkema (University of Guelph) demonstrated that when 28% UAN was applied with an AI nozzle there was an increase in visual crop injury (Table 1).

    He also showed that injury increased substantially when tank-mixed with herbicides and when nitrogen applications were delayed (Table 2). So, while AI nozzles are great for herbicide applications, they are not suitable for 28%. Growers should consider fall weed control to avoid the need for spring herbicide applications.

    Table 1. Potential yield loss associated with applying UAN 28% as overall broadcast treatment using FloodJet or TeeJet nozzles. 11 gallon (Imperial) = 1.2 U.S gal. Source: P. Sikkema, University of Guelph (RCAT), 2008–2013 (OMAFRA Pub 811: Agronomy Guide).

    Application CombinationVisual InjuryYield
    200 L/ha water (18 1g/ac water)0%6.4 t/ha (95 bu/ac)
    150 L/ha water + 50L/ha UAN (13.4 g/ac water +4.5 gal/acre UAN)3%6.4 t/ha (95 bu/ac)
    100 L/ha water + 100L/ha UAN (9 g/ac water +9 g/ac UAN)5%6.1 t/ha (91 bu/ac)
    50 L/ha water + 150L/ha UAN (4.5 g/ac water +13.4 g/ac UAN)7%6.1 t/ha (91 bu/ac)
    200 L/ha UAN (18 g/ac UAN)9%6.0 t/ha (89 bu/ac)

    Table 2. Crop injury (%) and yield (bu/ac) of winter wheat following an application of 28% UAN (400 L/ha) alone with air induction nozzles and with various herbicides compared to an untreated control that received the same amount of nitrogen. Source: Dr. P.H. Sikkema, 3 trials from 2008-2010, University of Guelph (Ridgetown Campus) – Additional information on tank-mixing with herbicides can be found here.

    TreatmentHerbicide rate/acInjury (%)Yield (bu/ac)
    control (unsprayed)——0105
    28% UAN alone——6105
    28% UAN + Infinity0.33 L9104
    28% UAN + Buctril M0.4 L8103
    28% UAN + Estaprop XT0.48 L9102
    28% UAN + Refine M12 g + 0.36 L1799

    Streamer Nozzles

    Streamers significantly reduce crop injury when applying UAN 28% in winter wheat. Growers in Ontario are using a range of 3, 5, 6 and 7 hole nozzles. These nozzles provide even coverage and minimize burn compared to flat-fan or flood nozzles; however, boom height can have an impact on crop injury. This is particularly important with 3 and 6 hole streamer nozzles. If there are significant variations in boom height (e.g. uneven emergence, uneven land, or a boom with excessive sway and yaw), significant crop injury can occur. This is exacerbated by hot and dry conditions.

    The damage is the result of non-uniform coverage. Streamers deliver spray in a triangular shape. If the boom is too low gaps in the spray pattern reduce coverage. If the boom is too high the crop may receive increased overlap, resulting in crop injury. Therefore, these nozzles are an excellent option for apply UAN 28% to winter wheat crop (see image below) as long as boom height can be managed effectively.

    Pro tip: 28-0-0 often has crystals so strainers are important.

    UAN 28% being applied uniformly to winter wheat using 3 hole streamer nozzles. Photo courtesy of: Jim Patton.

    Streamer Bars

    Streamer bars (see image below) may be the best choice. Streamer bars deliver liquid nitrogen to the crop vertically. This allows for even distribution across the winter wheat crop at various boom heights, often permitting great speed. Some even have a sliding orifice to permit an easy transition between rates. Research performed in Kentucky showed that streamer bars produced a 2.8 bu/ac yield advantage compared to 3 hole streamer nozzles, and a 4.9 bu/ac yield advantage over 7 hole streamer nozzles.

    Some may argue those aren’t significant yield advantages, but most Ontario growers would argue differently. Streamer bars provide uniform coverage no matter the state of emergence, boom height, topography or even wind conditions. Streamer bars can be adapted to most sprayers and are available in 15″ or 20″ spacing. The only caveat is that they can be fragile and can make folding the boom difficult.

    Chafer streamer bar. Photo courtesy of Alex Zelem.

    Other Ways to Reduce Burn

    In addition to proper nozzle selection there are a few things you can do to reduce the risk of crop injury from N applications.

    • Avoid applications of 28% when the crop is stressed or during hot and dry conditions.
    • If conditions are more conducive for crop injury, increasing water volumes or applying less N can also help reduce burn significantly.

    At the end of the day it is important to remember the end goal – maximize yield potential. If we can deliver UAN 28% as uniformly as possible to a standing winter wheat crop while minimizing crop injury, the 100+ bu/ac wheat crop will be well worth the effort.

    Here’s Peter Johnson (@WheatPete) to tell you more in this RealAgriculture Wheat School episode:

  • Evaluating Wheat Head Coverage from Two New Nozzles

    Evaluating Wheat Head Coverage from Two New Nozzles

    We’ve written extensively about angled flat fan nozzles and their ideal operating parameters (i.e. pressure, boom height, droplet size, volume and travel speed) for spraying wheat heads. Generally, coverage on the sprayer-approach side of a wheat head (aka the advance side) is easier to achieve because droplets from a conventional flat fan geometry tend to follow a downward-forward vector. Imagine dropping a ball from the window of a moving car. An outside observer would see it travelling forward as it fell.

    The back of the wheat head (aka the retreat side) and the sides are harder to hit. When we introduce a rearward angle to coarser, fast-moving droplets, the high momentum and downward-rearward vector deposits spray on the retreat side of the wheat head after the sprayer passes over. Mythbusters produced a cool video segment that illustrates this concept by matching the rearward velocity of a soccer ball to the forward velocity of a truck; the ball falls straight down. Of course, in our case we want it to shoot backwards.

    A great deal of independent research has determined that low booms coupled with dual fans that produce coarser spray and higher volumes will optimize coverage on any vertical target. Asymmetrical nozzles that have a more aggressive rearward angle perform better still. Of course both of these claims assume a “reasonable” wind speed, because the finer droplets in the spray experience a comparatively lower degree of inertia. Inertia is a property of matter that describes the resistance of an object to changes in its state of motion and it’s related to the object’s mass. What this means is that smaller droplets slow quickly, are easily deflected by wind, and tend to deposit on the windward side of the wheat head.

    So, maybe you already knew all that. What’s new?

    Two asymmetrical tips have been introduced in recent years and we wanted to characterize their coverage (Figure 1).

    The first is the “Fusarium Fighter” which is a combo-tip developed by Nozzle Ninja in Stettler, Alberta. It combines Pentair Hypro’s FC-3D100 (a non-AI tip with a 2 star rating from LERAP and a 100° wide fan) with ASJ’s, Compact Fan Low-Drift Coarse with its 120° wide fan. The 3D already has a 55° angle from vertical and the twin cap brings that to a very steep 65°.

    The second is Pentair Hypro’s Asymmetric Ultra Lo-Drift AI Ceramic. This is the same as the Lechler IDTA where the front angle is 120° wide, angled 30° forward from vertical and sprays 60% of the spray volume. The rear fan is 90° wide, angled 50° back and sprays the remaining 40%.

    Finally, and only to illustrate how symmetrical fans and finer droplets are perhaps not ideal for reliable wheat head coverage, we ran TeeJet’s TwinJet Twin TJ60-110VS. This is two 110° flat fans and the angle between them is 60° (30° fore and 30° back from vertical).

    Figure1. Evaluating coverage from three nozzles in winter wheat.

    For each treatment, five nozzles were positioned mid-boom on a Deere 410R to minimize any turbulence from the sprayer wheels and chassis and to reduce the degree of yaw. Extensions were used on all tips to ensure the spray did not impact the boom itself. All other nozzles were turned off. Nozzle bodies were on 50 cm (20″) centres and positioned 50 cm (20″) above the average wheat head. Travel speeds were selected to achieve 187 L/ha (20 gpa) at a pressure ideal for the tip in question and this is recorded in Table 1. Contractors and other such custom applicators may find these speeds low and the volumes high, but in this study we chose to emulate usage in smaller operations. The effect of travel speed on coverage is debatable but likely quite minor. More can be found on the subject in this article.

    NozzleSpray QualitySpeed Pressure
    AULD-C 11003C6.6km/h (4.1mph)483kPa (70psi)
    FF (CFLD-C02 & FC3D11003)VC & M8km/h (5mph)207kPa (30psi)
    TJ60-11004F8km/h (5mph)207kPa (30psi)
    Table 1. Operating parameters for three nozzles applying 187 L/ha (20 gpa) to wheat heads.

    The weather was 25°C, 40% R.H. and there was a very light and consistent tail wind of 2-4 km/h (1.2-2.4 mph). These were ideal conditions because it was not hot or dry enough to evaporate finer spray appreciably, and not windy enough to deflect the spray.

    Water sensitive paper (Syngenta) was wrapped around the wheat head and held by a paper clip (see Figure 2). This gave a panoramic representation of coverage. Two more were mounted nearby on a length of rebar at wheat head-height; One faced the sprayer advance and one faced the retreat. Three such sets were positioned inline, spaced about 1 m apart and centered on the swath produced by the five nozzles. This was repeated 2x for each nozzle. Papers were retrieved, digitized and analyzed per the method described in this article.

    Figure 2. WSP wrapped around a wheat head.

    The resultant coverage is recorded in Table 2 and graphed in Figures 3 and 4.

    NozzlePanoramic:
    Area covered (%)
    & deposit Density (#/cm2)    		Advance:
    Area covered (%)
    & Deposit density (#/cm2)    		Retreat:
    Area covered (%)
    & Deposit density (#/cm2)
    AULD-C 1100310.2%
    130.4 deposits/cm2    		7.9 %
    56.1 deposits/cm2
    		11.1%
    87.7 deposits/cm2
    FF (CFLD-C02 & FC3D11003)13%
    97.5 deposits/cm2    		9.0%
    46.9 deposits /cm2    		18.3%
    72.4 deposits/cm2
    TJ60-1100422.3%
    471.0 deposits/cm2    		21.5%
    320.9 deposits/cm2    		11.4%
    286.1 deposits/cm2
    Table 2. Average coverage from three nozzles applying 187 L/ha (20 gpa).
    Figure 3. Comparison of average percent area covered for three nozzles.
    Figure 4. Comparison of average deposit density for three nozzles.

    Unless you are experienced with interpreting coverage data, these numbers and graphs may not convey what coverage truly looked like. And since we saw some unexpected results, we felt it would be best to digitize the papers from each nozzle and create graphics to support our observations and opinions on how they performed. Each image shows six replications of each orientation. We’ll begin with the AULD in Figure 5.

    The AULD was operated at a relatively high pressure to create the Coarse droplets recommended by the nozzle manufacturer. The steep rearward angle produced a higher degree of coverage on the retreat side compared to the advance. The streaky or tear-drop shaped deposits indicate a droplet that “scuffed” along the paper surface, almost but not quite in parallel. On the panoramic targets they tend to correspond with the sides of the paper, where the droplets are not aimed directly at the surface as in the “advance” and “retreat” surfaces. All in all, this nozzle performed well and created droplets large enough that we feel they would stay on course in a higher wind and not get tied up on the awns of the wheat head.

    Figure 5. Digital scans of water sensitive papers from the AULD nozzle. Spray quality was C.

    Next is the Fusarium Fighter. This nozzle was developed in Western Canada where, on average, sprayers tend to travel faster than they do in Ontario. Certainly this isn’t the case for all Ontario fields, but we chose to emulate usage in home farm operations where fields may be smaller and less level. This is relevant because faster travel speeds permit the use of a larger 3D nozzle to achieve 20 gpa, which in turn produces a coarser spray quality. In our trials, we traveled more slowly and that necessitated a smaller 3D that produced only a Medium droplet size. We hypothesized that those smaller droplets may not stay on course, but the papers show otherwise (Figure 6).

    Figure 6. Digital scans of water sensitive papers. Spray quality was VC and M.

    Coverage on the retreat side was very good and far outstripped the coverage on the advance side. In fact, the Very Coarse spray quality from the CFLD-C may be too large. Dropping from VC to C would create more droplets and a higher deposit density on the advance. We did see some gaps in the panoramic papers that likely reflect the lack of finer droplets which tend to move more erratically and contact the sides. Recall that we said weather conditions were ideal. It is still questionable how well a 3D producing a Medium spray quality would perform in windier conditions or on the boom ends where yaw tends to lift tips well above the ideal operating height.

    Figure 7. All three tips operating on a stationary sprayer at 40 psi. The Fusarium Fighters (foreground), the TwinJets (middle) and the AULDs in the background.

    Finally, the TwinJets (Figure 8). We used this nozzle only to demonstrate how the lack of an aggressive rearward angle and a Fine spray quality was not conducive to reliable wheat head coverage. Many studies have demonstrated that such a nozzle outperforms a single, conventional flat fan, but it is not the best choice of angled nozzles. Once again recall that these nozzles were positioned centre-boom where yaw and sprayer-induced turbulence were not an issue and in absolutely ideal environmental conditions.

    We saw tremendous coverage on the advance side and while we saw comparatively less on the retreat side, it still performed well compared to the other nozzles. The panoramic targets also indicated suitable coverage, both as percent area covered and deposit density. BUT, if we have some questions about how the Medium spray from the 3D would perform in more challenging conditions, we are far more concerned about the fines from this tip. Having used this nozzle in past demonstrations we are well aware of how non-uniform and erratic coverage can be, and that translates to poor efficacy and increased drift. However, sometimes circumstances conspire to create exceptions, and the coverage we saw in this trial is hard to fault.

    Figure 8. Digital scans of water sensitive papers. Spray quality was F.

    This trial was not intended to rank nozzles, but to explore the merits of a few new designs and evaluate their respective coverage. If anything the results reinforce the need to operate angled sprays correctly and in appropriate weather conditions. Water sensitive paper remains a quick and easy method for sprayer operators to evaluate their own coverage and inform any corrective actions to improve results in their own unique circumstances.

    Thanks to Dan and Paul Petker (Petker Farms) and Don Murdoch (Simcoe Research Station, University of Guelph) for providing the fields and operating the sprayers. Nozzle Ninja is gratefully acknowledged for the donation of AULD and Fusarium Fighter nozzles, and Spraying Systems Co. for the TwinJet nozzles and water sensitive paper.

  • Avoiding Skips from PWM Sprayers

    Avoiding Skips from PWM Sprayers

    Does this sound familiar?

    “This year was the first year we used a growth regulator on our wheat. After heading, we noticed a wavy pattern of different plant heights between 30 and 45° to the operating direction. It was only a couple inches difference and was difficult to photograph. We sprayed 12 gpa at 9 mph using TT11005 nozzles alternating forward and back at 35 psi and a 70% duty cycle. I’ve talked to other operators in Canada and in Europe and several customers have reported seeing this pattern, no matter which model of PWM sprayer. What’s happening?”

    Skips in cereal that are obvious to the eye can be difficult to photograph.

    The pulse width modulation is very likely responsible for the waves. We have a number of articles describing how PWM works, but here’s a brief recap of the relevant bits.

    A solenoid intermittently interrupts nozzle flow with a frequency between 10 and 100 times per second (depending on manufacturer). The proportion of the time the nozzle remains open is called the Duty Cycle. Each nozzle is linked to the neighbouring nozzles so that when one pulses on, the neighbour pulses off. So although you may only have half the nozzles spraying at any moment in time, sufficient overlap ensures there are no gaps in the pattern.

    However, depending on the combination of frequency and duty cycle, it is possible to lose that overlap between nozzles. This can cause a checkerboard pattern that appears to repeat in a diagonal line. The following two images are from www.Capstanag.com and they illustrate an ideal overlapping pattern and a pattern that creates skips.

    Here’s a 11008 at 10 gpa, 15 mph, 60% DC, 10 Hz, 21” boom.
    Here’s an 8008 tip at 5 gpa, 15 mph, 30% DC, 10 Hz, 21” boom.

    We can also sometimes see skips on the outer edges of sharp turns. In that case the outer boom section can be travelling two or three times as fast as the cab. In a conventional system, this would produce under-dosing in the outer region and over-dosing closer to the cab.

    Some degree of skipping may be more common than we realize. It’s only when we spray products that produce obvious visual symptoms at low doses that we can see a biological response. In the case of plant growth modifiers used to prevent lodging in cereals, we have a perfect storm situation. A region of reduced spray overlap, applied at a time when the crop is elongating rapidly, perhaps on rolling ground from an unstable boom height, can all conspire to create regions of reduced dose with striking visual symptoms.

    The following list describes conditions that can increase the potential for skips, and what you can do to avoid them.

    1. Low duty cycles. Cycles less than 60% should be avoided.
    2. Fast travel speeds. Faster speeds may help blend the spray in the swath a little, but too fast can create gaps and increase drift potential. At high travel speeds the system is usually operating at a high duty cycle unless an especially large nozzle size has been selected. Ideally, we want to run the duty cycle at 60-80%, but there are always exceptions. For example, according to Wilger, 90-92% is fine when you run at 20 gal/ac with their “15 gal tips”.
    3. Low booms. The lower the boom, the less overlap. Raising the boom to 24″ above the crop may help, but beware of drift.
    4. Narrow fan angles. Nozzle angles less than 110° reduce the degree of overlap and are less forgiving if the distance between nozzle and target decreases.
    5. Low pressure. Avoid operating at pressures below 35 PSI. Due to pressure drop at the solenoid, 40 PSI on the monitor might mean 28 PSI at the nozzle. Some nozzle tables account for solenoid-induced pressure drop and some do not. Low pressure may be insufficient to establish the full 110° pattern, and the resulting marginal overlap not only means inconsistent dose, but inconsistent droplet size because droplets are coarsest at the edge of the pattern. And, if that’s not already enough, note that air induction nozzles intended for use with PWM tend to create messy patterns at low pressures and low duty cycles.
    6. Especially coarse spray quality. Unless the label requires it, consider using spray qualities no larger than Very Coarse, particularly at low volumes. PWM frees the operator to use pressure independent of rate, so you may be able to accomplish this without swapping nozzles.
    7. Products that are highly dose-dependent. This one is likely unavoidable, but be aware they are the products most likely to produce obvious visual symptoms. In the case of PGR’s, we have not (yet?) seen any evidence that skips translate to reduced yield. Weed misses or sub-lethal doses of fungicide or insecticide might be another matter.