Development of a phase-doppler technique for mass balance and spray characterisation of orchard air-blast sprayers within New Zealand horticultural cropping systems

The knowledge of the sprays emitted from orchard air-blast sprayers has historically been assessed using an array of samplers to capture airborne particles such as various strings/ribbons, paper material, and/or patternation structures. While these methods provide flux data, no other information is obtained which is pertinent to understand the potential movement of droplets. Qualitative droplet information can be acquired in situ which can be related to the deposition, coverage, and off-target losses. However, the quantitative analysis for agricultural sprays has predominately been conducted in a laboratory setting with the use of laser devices which are comprised of multiple pieces; ergo the necessity for controlled environments for the alignment of these pieces is essential. In this research, a new self-contained phase Doppler (pD) was tested to assess the droplet size spectrum, velocity, and flux in uncontrolled outdoor field conditions with the overall hypothesis that the pD will be a superior means of data collection in that the data will be more robust with fewer sources of error, highly repeatable, fast, and inexpensive. To test this hypothesis, a step-wise research plan was developed to determine 1) if pD could accurately measure flux by traversing through a similar spray plume to an orchard sprayer while still in the controlled setting of a laboratory; 2) compare and validate pD derived flux data to that of passive strings collectors in a wind tunnel in areas of heightened flux and droplet/air velocities; 3) compare these samplers in outdoor environments with no crop presence; and 4) determine if pD could be used in place of other collectors in a horticultural setting. Results demonstrated an average error of the computed flux versus measured flow rate was -3.3% using a disc core (D1/DC33) hollow cone nozzle at spray pressures of 3.1, 4.1, and 5.2 bar pressure (45, 60, and 75 psi) and at five heights (10, 20, 30, 40, and 50 cm). In the wind tunnel with varying wind speeds (1.4, 4.2, 8.3, 12.5, and 16.7 m/s) and spray exposures times (5, 10, 15, 30, and 60 s), the pD accurately measured the spray flux while the string samplers overload with saturation. From here, the pD was taken outdoors and displayed that the sampling volume of the pD was too small to acquire enough samples for sufficient flux data; therefore this research ceased. However, in all of these studies, regardless of the sampling frequency and inadequate flux output, important data was still acquired related to the droplet size distribution and droplet velocity. This is thought to be a major point of difference whereas pD may not yet be able to be the sole tool, but an important support tool for other instruments that can only measure flux. Lastly, the ability to quantitatively understand the droplet size differentiations at various heights and distances in relation to a crop can provide profound feedback to the application of plant protection chemistries, their fate, and their efficacy

Discharge coefficients of flat-fan nozzles

The discharge coefficient (Cd) is a measure of how much of the pressure energy of a nozzle is converted into kinetic energy. With the discharge coefficient known, the exit velocity of the liquid sheet from the nozzle can be calculated from the pressure. It is important to be able to accurately calculate this nozzle exit velocity for use in initializing computational simulations such as AGDISP or CFD. The objective of this work was to measure the discharge coefficients for different types of flat-fan nozzles. In this work, a phase-Doppler interferometer was used to measure the exit velocity for standard, pre-orifice, and air-induction flat-fan nozzles, for rated sizes from 01 to 06, at pressures from 1 to 6 bar. From these velocities, discharge coefficients were calculated. The standard flat-fan nozzles had the highest discharge coefficients, while the air-induction nozzles had the lowest discharge coefficients. For a fixed type of nozzle design, the discharge coefficient increased slightly with the rated flow rate. The discharge coefficient decreased slightly with increasing pressure for a given nozzle. Much of the differences in droplet size for different types of nozzles can be explained by atomization theory as a result of the differences in discharge coefficients for the different nozzle designs

Exclusion zones for variable rate nitrogen fertilisation in grazed dairy pasture systems in New Zealand

To assess the variability of total soil nitrogen (TN) on grazed and irrigated pastures, TN was quantified from spatially distinct “areas” within the paddock (irrigated and non-irrigated areas, around the gates, and around the troughs) on two dairy farms located in Canterbury, New Zealand. During soil sampling, each area was sub-divided and multiple soil samples were taken to ensure adequate spatial representation of each area. The results showed there were no differences in TN between the farms, but differences were detected between the paddocks (P< 0.001), largely due to the significant interaction between the areas (gates and troughs) in different paddocks (P< 0.001). The greatest variability in TN was around the gates, due to either much higher or lower TN near the entrance of the gates. The TN levels returned to concentrations that were similar to those in the surrounding pasture after 4 m distance from the gates. This study shows while TN concentrations are relatively consistent spatially within pastures, there is high variability in TN in proximity to some farm infrastructure, such as gates and troughs

Evaluation of spray drift with an experimental ultrasonic sensor sprayer in a dwarf apple orchard

Dwarf apple trees are becoming more common in New Zealand due to their easier maintenance and more efficient production. However, this may increase the risk of spray drift if orchardists’ do not adjust spraying practices to match shorter dwarf varieties of fruit trees as compared with larger more traditional canopies as dwarf trees have less foliage to intercept spray. A study was carried out to examine the off-target movement of the spray plume from a conventional air-blast sprayer as compared with an experimental ultrasonic sensor sprayer in a dwarf apple canopy. The experimental sensor sprayer was set up to respond to the target canopy. Three treatments were carried out including a conventional Typhoon 1500 orchard sprayer, a single row ultrasonic sensor sprayer with either sensors ON or OFF. Each sprayer was set to deliver 500 L/ha of a 0.4 g/L concentration of a fluorescent dye (PTSA, 1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt). The drift was quantified by using a series of mylar cards, petri dishes and fishing nylon. Results indicated a 24% decrease of deposited drift from 1 to 100 metres with the sensors turned on and a 5% increase with the sensors off as compared to the conventional sprayer

Evaluation of spray drift in potatoes using various spray delivery systems

Spray deposition has previously been studied within a potato canopy. In a follow-up study, spray drift was evaluated using three treatments from the previous research plus two treatments encompassing an additional grower standard and a spray drift standard. Treatments included (1) an air-assisted Gambetti sprayer with full-cone nozzles applying spray at a rate of 400 litres/ha, (2) a rotary atomizer spraying system (Proptec) applying spray at a rate of 200 litres/ha, (3) a drop-leg application spraying above (25%) and below canopy (75%) at 260 litres/ha, (4) a conventional hydraulic nozzle spray boom with Guardian AIR™ Twin nozzles applying 200 litres/ha and (5) a conventional hydraulic nozzle spray boom with standard 11003 nozzles at 300 litres/ha. Data were normalized per nozzle and application rate (200 litres /ha). With the exception of the Gambetti application, results indicated a similar pattern with very low deposition beyond 10 m downwind. The Gambetti results showed very low deposition near 0 m and spray cloud reaching 40 m, but it is believed that the turbulent airflow from the Gambetti sprayer adversely affected the deposition samplers through a high level of disturbance, so more data are necessary for further analysis of this effec

Spray drift modelling using field-measured PDI laser techniques

The modeling of airborne spray drift and ground deposition to off-target areas requires a knowledge of the initial source of particles such as the emission droplet size, velocity and flux spectrum (the particle cloud “available” to drift after any deposition on the intended target), the transport conditions of the spray such as the wind speed, direction, temperature and relative humidity as well as atmospheric stability, and any spray interception by foliage, vegetation and other structures. Established models such as AGDISP are widely used in North America and Australia for such modelling of conventional sprays, but currently include mainly aerial application platforms with some preliminary ground boom sprayer options. The spray release direction for these aerial and ground boom sprayer scenarios is downwards. Tree and vine crops sprayers involve spray release in several directions including down, sideways and upwards. AGDISP does not offer a way to model the latter and there are no “buttons” to press in the models to cover many drift reduction technologies (DRTs) such as addition of a hood, cover, shroud, shield as an equipment modification or the addition of an electrostatic charge. Certain other DRTs such as evaporation reduction systems or narrow droplet size spectra atomizers can be accommodated in the AGDISP model through input of these variables in the appropriate model screens. A modified ground modeling system called WTDISP was described by Hewitt (2008). However, the model is limited to use with wind tunnel data only and has not been used for spray deposition modeling because the inputs cannot all be measured using the preferred single measurement system of monofilament lines. A new approach to data collection for this model is discussed in the present paper, based on a Phase Doppler Inteferometer (PDI) developed for the measurement of sprays in the field and in wind tunnels. The measured droplet size and flux data can be processed to distances of up to 100 m. Validation against field deposition data to distances up to 200 m will allow future extensions of the model range to encompass most DRT interest in Australia and New Zealand

Phase doppler flux comparisons

The movement of droplets in time and space (i.e. flux) is essential to know when measuring and/or predicted spray drift via agricultural application. A study was performed to assess the flux measurements of a phase Doppler system against the standard string derived flux in a wind tunnel. The primary objective of the study was to compare flux from a new phase Doppler system against 1.7 mm cotton and 2.0 mm nylon strings at varying wind speeds (5, 15, 30, 45, and 60 km/h) and spray exposures times (5, 10, 15, 30, and 60 s) with an overarching hypothesis that the active, phase Doppler would be able to accurately measure the flux regardless of exposure and spray mass whereas the static string samplers will be limited to an undefined maximum retention. The phase Doppler did measure as linearly as expected, however strings did not reach a point in which they loss mass; conversely, they appear to be overloading. These findings are believed to be among many variables which influence the high variance of past mass balance works reported in the literature

Phase Doppler quantification of agricultural spray compared with traditional sampling materials

The quantification of spray mass has historically been accomplished by means of fluorescent dyes and various string and ground samplers to capture the dye-laden spray. However, these methods are typically not used in close proximity to orchard sprayers and are prone to many sources of error. The objective of this study was to assess the ability of an in-field phase Doppler (pD) interferometer to quantify spray mass against two common string samplers. Measurements were taken at 0.5 m increments to 4.5 m vertically and 1.0 m increments to 5.0 m downwind from the spray. Converted flux measurements from the strings were compared with those obtained using the pD interferometer. The current pD technology was found to be incapable of collecting equivalent flux data to that obtained from the strings. However, the pD equipment did provide useful data on droplet velocity and size

Evaluation of spray deposition in potatoes using various spray delivery systems

The tomato-potato psyllid incurs high control costs through intensive spraying and other treatments. A field study was conducted in March 2012 in Pukekohe, New Zealand, to evaluate the pesticide deposition potential of five different spray delivery systems. The treatments included a conventional boom, a canopy submerged drop sprayer combination, a pneumatic electrostatic spraying system, an air-assisted rotary atomizer, and a high-volume air-assist boom. Each system was calibrated for appropriate spray volume rates between 167 and 400 litres/ha. Rhodamine WT fluorescent dye used as a tracer was sampled on folded Kromekote® sampling cards oriented flat and horizontally above, central to, and below the canopy. Spray coverage rates were quantified at designated heights adjacent to leaves to assess deposition throughout the potato canopy. All treatments that consisted of one or more novel technologies consistently gave higher coverage to the underside of the potato leaves than with the conventional boom

A new Phase Doppler Inteferometer system for evaluation of pesticide sprays in the field

A new approach is proposed for modeling droplet deposition downwind of spray application areas for almost any pesticide application technique using initial field measurements of the size/ velocity profile of the spray which is still airborne downwind of the intended target. A field Phase Doppler Inteferometer (PDI) system has been developed for measurements of these sprays at different heights under field conditions. The size and velocity data can then be input to existing modeling algorithms such as the AGDISP Lagrangian solution code which then tracks particle transport, evaporation and deposition downwind of the spray release point. Libraries of data for various spraying systems can be linked with the model for future spray drift exposure risk assessments that will facilitate decision-making on safe-ty measures such as application recommendations or the size and location of no-spray buffer zones for specific pes-ticides and non-target sensitive areas. The present paper describes this process and provides examples of data meas-ured in field studies using the modified PDI system. The work is ongoing and the present paper is aimed at describ-ing the development of the sampling systems through field studies in New Zealand and the USA. Future research will focus on comparison of modified AGDISP model predictions of spray deposition using measured droplet size/ velocity data against actual field study deposition data in several application scenarios and crop types