M. De Schampheleire

The Influence of Operator-Controlled Variables on Spray Drift from Field Crop Sprayers

Spray drift can be defined as the quantity of plant protection product that is carried out of the sprayed area by the action of air currents during the application process. This continues to be a major problem in applying agricultural pesticides. The purpose of this research is to measure the amount of sedimenting drift from a horizontal boom sprayer for different (drift reducing) spray application techniques under field conditions and to compare the results with the results from a reference spray, taking into account variations in meteorological conditions during the field drift experiments. Field drift measurements were performed for several combinations of nozzle type (standard flat-fan, low-drift, air inclusion) and size (ISO 02, 03, 04, and 06), spray pressure (2.0, 3.0, and 4.0 bar), driving speed (4, 6, 8, and 10 km h-1), and spray boom height (0.3, 0.5, and 0.75 m ) according to ISO 22866 by sampling in a defined downwind area at 24 different positions using horizontal drift collectors. The reference spray was defined as a standard horizontal spray boom without air support, a spray boom height of 0.50 m, a nozzle distance of 0.50 m, ISO 110 03 standard flat-fan nozzles at 3.0 bar (1.2 L min-1), and a driving speed of 8 km h-1, resulting in an application rate of approximately 180 L ha-1. Nozzle type as well as spray pressure, driving speed, and spray boom height, have an important effect on the amount of spray drift. Larger nozzle sizes, lower spray pressures and driving speeds, and lower spray boom heights generally reduce spray drift. Concerning nozzle types, air inclusion nozzles have the highest drift reduction potential, followed by the low-drift nozzles and the standard flat-fan nozzles. Drift results are closely linked with droplet size characteristics of the sprays.

Drift from Field Crop Sprayers Using an Integrated Approach: Results of a Five-Year Study

Spray drift continues to be a major problem in applying agricultural pesticides. This article summarizes the results of a five-year study of drift from field crop sprayers using a unique integrated approach. Indirect (spray quality and wind tunnel measurements) and direct (field) drift experiments were performed, and drift models were developed to study the effect of spray application technique, droplet characteristics, buffer zones, meteorological conditions, spray liquid properties, border structures, and crop characteristics on drift from field crop sprayers. It was found that indirect drift measurements can be a valuable alternative to field drift experiments. A validated 3-D computational fluid dynamics (CFD) mechanistic drift model was developed, which can be used for a systemic study of different influencing factors. This model was reduced to a fast 2-D diffusion advection model, which is useful as a hands-on drift prediction tool. From the experiments as well as from the models, the fraction of small droplets and the spray boom height were found to be the most influential spray application factors. Moreover, meteorological conditions as well as crop characteristics have an important effect on the amount of spray drift, which can be reduced significantly using intercepting screens or buffer zones. From this study, drift protocols, data, and models are made available, which help to understand and reduce the complex phenomena of spray drift.

Droplet Size and Velocity Characteristics of Agricultural Sprays

The quality of agricultural sprays plays an important role in the application of plant protection products. For 13 nozzle-pressure combinations, droplet size and velocity characteristics were measured 0.50 m below the nozzle using a PDPA laser-based measurement setup. Nozzles were mounted on a transporter to sample the whole of the spray fan. The effects of nozzle type (standard, low-drift, and air-inclusion), nozzle size (ISO 02, 03, 04, and 06) and operating pressure (2.0, 3.0, and 4.0 bar) were tested. Measured droplet sizes and velocities were related, and both were affected by nozzle type, size, and operating pressure. Droplet velocities at 0.50 m were determined by their size and initial ejection velocity. In general, bigger droplet sizes correspond with higher droplet velocities, and smaller droplets with lower droplet velocities. Important differences in velocities were observed depending on the nozzle type and size, both affecting the ejection velocity. For the same droplet size, droplet velocities were highest for the flat-fan nozzles, followed by the low-drift nozzles and the air-inclusion nozzles (because of the lower ejection velocities caused by pre-orifice and Venturi effects). Similarly, the bigger the ISO nozzle size, the faster were the droplets of the same size. Droplet velocities of the larger droplet sizes (>400 µm) varied from about 4.5 to 8.5 m s-1 depending on the nozzle type and size. Below 400 µm, droplet velocities consistently decreased with the decrease in droplet size, and vary from 0.5 to 2 m s-1 depending on the nozzle type and size. All this information is very useful with regard to crop penetration, the risk of spray drift, and the quantity and distribution of the deposit on the target.