D. Downey

HERBICIDE MICRO-DOSING FOR WEED CONTROL IN FIELD-GROWN PROCESSING TOMATOES

Weeds within the seedline area and in close proximity to crop seedlings are highly competitive and reduce crop yield. When chemically selective herbicides are unavailable or ineffective, spatially selective removal is required and is often a manual operation. Automation of selective weed removal requires sensing and actuation systems. Image and spectral analysis can discriminate weeds from crop plants while precise dosing methods are required for automated treatment of small, distinct weeds. A pulsed-jet, micro-dosing actuator was developed to apply liquid herbicide treatments. The biological performance of micro-dosing was evaluated in field-grown processing tomatoes with a nonselective herbicide (glyphosate) in mixtures including surfactants and splash-inhibiting polymers. Liquid dose rates were 37 .L/cm2 for treatment areas of 6.3 . 12.5 mm. Pulse durations were 6 to 10 ms. A formulation including a surfactant and a polymer provided efficacy while reducing splash, i.e., “micro-drift” that caused phytotoxicity to adjacent crop plants. When treated with the micro-dosing system, splash-related phytotoxicity produced greater yield suppression than competition from escaped weeds. The results established that use of non-selective herbicides for micro-scale dosing of weeds during early crop growth is a feasible alternative to broadcast application of chemically-selective herbicides. The optimal point of crop and weed growth for using a weed-sensing, one-pass post-emergent control system requires understanding of crop development, weed competition, and the ability of the crop to recover from inadvertent splash of micro-dosed materials.

Finite element analysis of particle and liquid flow through an ultraviolet reactor

A computational fluid dynamics program was used to simulate liquid flow through an ultraviolet (UV) reactor. Salt tracer tests were performed at different flow rates to validate results from the program. Temporal and spatial descriptions of particle trajectories from the flow model were used to quantify flow pathways through the UV reactor. Particle trajectory information was then used in a separate numerical program to estimate temporal distribution of particles exiting the domain during discrete time steps for the flow solution. From these data, the exit time for particles transported through the modeled flow domain were compared with experimental tracer results. At low flow rates, the simulation results were within 95% confidence intervals established from the experimental data. At higher flow rates, the simulation results tended to predict a shorter exit time for particles than that observed experimentally with salt tracer studies. The results of this research can be used to compare UV disinfection efficacy on low transmission liquids without the need for extensive experiments or construction of prototypes.

Digital device and technique for sensing distribution of spray deposition

Assessment of spray deposition often relies on the use of water- and oil-sensitive paper or other stain-based techniques to document extent of coverage and distribution. The procedure requires the placement, collection, scanning, and post-processing of deposition stains on cards, and is time consuming and labor intensive. An electronic sensor, coupled with a wireless network for transmission of in situ data, would have great advantages over current methods typically used in spray deposition research. A prototype technique and sensor for detecting and quantifying spray deposition were developed and evaluated. The device is capable of sensing the presence and location of multiple droplets on a sensor surface, is reusable and potentially inexpensive. The sensor detects the presence of discrete fluid droplets on the sensor surface when droplets complete electrical circuits positioned in an array. The sensitivity of the system is controlled by setting a reference (threshold) voltage in a voltage comparator circuit, while spatial sensitivity is determined by the physical separation of sensing points on the sensing array. The sensor differs from previously reported designs in that the deposition is quantified as a series of discrete, digital indications instead of a spatially integrated response. This capability allows spatial distribution of spray, not just an estimate of quantity, to be determined. The sensor was tested using spray applications of fine, medium, and coarse ASAE standard sprays. The performance of the sensor prototype, defined as measurement of covered area of stain deposition, was best when detecting coarse sprays. Future development will include fabrication of a sensing array with a higher spatial resolution of sensor pads, incorporation of more elegant algorithms for detailed scans of the sensing surface, and interfacing the sensor with a wireless communication system.

Evaluation of particulate matter abatement strategies for almond harvest.

ABSTRACT Almond harvest accounts for substantial PM10 (particulate matter [PM] ≤10 μm in nominal aerodynamic diameter) emissions in California each harvest season. This paper evaluates the effects of using reduced-pass sweepers and lower harvester separation fan speeds (930 rpm) on lowering PM emissions from almond harvesting operations. In-canopy measurements of PM concentrations were collected along with PM concentration measurements at the orchard boundary; these were used in conjunction with on-site meteorological data and inverse dispersion modeling to back-calculate emission rates from the measured concentrations. The harvester discharge plume was measured as a function of visible plume opacity during conditioning operations. Reduced-pass sweeping showed the potential for reducing PM emissions, but results were confounded because of differences in orchard maturity and irrigation methods. Fuel consumption and sweeping time per unit area were reduced when comparing a reduced-pass sweeper to a conventional sweeper. Reducing the separation fan speed from 1080 to 930 rpm led to reductions in PM emissions. In general, foreign matter levels within harvested product were nominally affected by separation fan speed in the south (less mature) orchard; however, in samples conditioned using the lower fan speed from the north (more mature) orchard, these levels were unacceptable. IMPLICATIONS The results of this research indicate that PM emissions from almond sweeping operations may be reduced by use of reduced-pass sweepers. Additionally, increased efficiencies in fuel consumption and time required for sweeping may be realized by use of reduced-pass sweepers. Reducing harvester separation fan speeds results in lower emissions from nut conditioning, but foreign matter levels in conditioned samples from more mature orchards were unacceptable.

Direct nozzle injection of pesticide concentrate into continuous flow for intermittent spray applications

A direct nozzle injection system was developed to intermittently inject concentrated solutions into continuous carrier liquid flow through a straight-stream spray nozzle used for targeted roadside spraying of post-emergent herbicide during pre-emergent herbicide application. The injection system was based on a 12 VDC direct-acting electrical solenoid valve with a 0.56 mm valve orifice and metering plate with a 0.2 mm diameter orifice. A conductivity-based sensor was used to measure the instantaneous concentration of NaCl tracer simulating a pesticide solution. Injection pulse durations ranged from 10 to 100 ms into carrier flows of 1.5 and 2.6 L/min from 1.55 and 2.18 mm nozzle orifice diameters, respectively. Lag times between initiation of the injection valve actuation and emission of the concentrate material from the spray nozzle were on the order of 25 ms. Concentrations of 1% (v/v) from injected solution into the flow emitted from the nozzle could be achieved within 100 ms after valve actuation. Increasing the injection pulse duration did not reduce lag time nor increase the temporal rate of concentration increase in the emitted spray; however, increasing the injection pressure increased the rate of concentration increase. Analysis of the injection event, using standard mixing criteria, determined that the injection mixing events were Gaussian in nature and did not represent ideal plug flow or short-circuiting events. For an intermittent, target-detecting system with a detector-to-nozzle distance of 4 m and a ground speed of 5 m/s, the direct nozzle injection system is a feasible configuration for spot spraying if the sum of detection time and time of flight for the emitted spray is less than 800 ms. For a prototype machine vision-based roadside sprayer, detection and spray flight times were less than 67 and 400 ms, respectively; therefore, feasibility of spot spraying using at-nozzle injection was established.

Injection and fluid handling system for machine-vision controlled spraying

A fluid handling system was developed to allow on-demand chemical injection for a machine-vision controlled sprayer. Critical design parameters were to maintain a desired concentration of chemical within the solution and to maintain a constant spray pressure at the nozzles. Unlike conventional agricultural spray injection systems which are designed to respond to relatively slow vehicle speed changes within a relatively narrow range, the system reported in this paper was designed to respond quickly over a wide dynamic range of flowrates. The design was evaluated with two injection rate control methods for accuracy of maintaining a desired concentration and response speed over a prescribed range of flowrate changes, simulating a “real world” weed map. A salt tracer was used to determine concentration changes in real time and spray pressure was recorded using an electronic transducer. The applied concentration was maintained within about 10 % of the desired rate and pressure varied 5 % over a dynamic flow range of 12:1.

INJECTION MIXING SYSTEM FOR BOOMLESS, TARGET–ACTIVATED HERBICIDE SPRAYING

An injection mixing system for herbicide solution was developed for a target–activated spray system designed for roadside weed control. Commercial components were used for fluid handling, and two interface techniques were developed for communication between the target sensing sprayer and the injection system. An electronic technique used digital scaling of the relative weed load to characterize and initiate changes in relative injection rate of active ingredient. The alternative mechanical technique relied on fluid coupling between the spray emission and the injection systems to maintain the desired concentration of active ingredient in the spray mix. Performance of the injection system was evaluated using salt tracer as the injection solution and in–line liquid conductivity measurements to determine concentration. Response, stability, and steady–state accuracy of the system were quantified over a 12:1 turndown ratio at command rates of 0.5 to 10 Hz. Both interface techniques maintained desired tracer concentration within 10% of the target level when subjected to highly variable weed loads. The electronic technique provided faster response and the possibility for feedforward control. Liquid pressure at the nozzle manifold was maintained during the rapid changes in spray emission by using 3–way valves to shuttle flow between the spray nozzle and a bypass line. Nozzle pressure remained within 10% of the desired value during the dynamic testing. The fluid handling and injection control systems were transparent to the operator and required no changes to the operator interface typically used for conventional spraying.

Quality Control Verification and Mapping System for Chemical Application

The quality of an agrochemical application is a combination of the efficacy of the deposit, the productivity of the operation and the avoidance of off-site movement. Potential environmental contamination from chemical application is influenced by the characteristics of application and proximity to sensitive areas. When small droplets, high spacing of boom above target or high ground speeds are used, off-target movement can increase. Similarly, when the application vehicle is near field boundaries or in significant wind conditions, off-target movement is more likely. Current GPS and GIS technology allow critical parameters of application to be sensed and recorded along with vehicle location. From these data, “quality control maps”, that is, historical records of the application can be generated and used to establish driver productivity, regulatory compliance or efficacious application.

AN ELECTRONIC SENSOR TO CHARACTERIZE TRANSIENT RESPONSE OF NOZZLE INJECTION FOR PESTICIDE SPRAYING

An electronic sensor was developed to characterize the transient response of a two-fluid mixture spray emission created by injecting a pulse of concentrated solution into a carrier fluid within a spray nozzle. The test situation simulated an intermittent, at-nozzle chemical injection system for spraying of distinct targets. The principle of sensor operation was measurement of the electrical resistance of an element of the emitted fluid created by injecting a concentrated sodium chloride solution into a water carrier. The sensor was initially calibrated with steady-state flow of carrier liquid over a range of 10 to 1500 ppm NaCl concentration. The high temporal response of the sensor provided measurement of the transient concentration of injected NaCl solution during brief (10 to 100 ms) injection events into the steady-state flow of the carrier liquid. The accuracy and transient response were quantified by comparing the volume of injected salt solution as determined by integrating the instantaneous concentration over the measured event with a direct volumetric measurement of the injected volume. Excellent agreement between volume measurements of injection and predicted injection volumes was found, validating sensor use for injection studies. The relatively simple sensor design provides the accuracy and high-frequency response necessary for at-nozzle injection studies.