Investigation on optimal spray properties for ground based agricultural applications using deposition and retention models

In crop protection, it is well known that droplet size determine spray efficacy. The optimisation of both spray deposition and retention leads to a dilemma: should small droplets be used to increase retention or large droplets be preferred to avoid drift? An ideal droplet should have a short time of flight to minimise its distance travelled while impacting the target with a moderate kinetic energy. This paper aims to determine an optimum range of droplet sizes for boom-sprayer applying herbicide using a modelling approach. The main parameters of spray deposition and retention models are systematically varied and the effects on drift potential and droplet impaction outcomes are discussed. The results of the numerical simulations showed that droplets with diameter ranging between 200 μm and 250 μm offer high control of deposition by combining a low drift potential and a moderate kinetic energy at top of the canopy. A fourfold reduction of the volume drifting further than 2 m from the nozzle was observed for a spray with a volume median diameter of 225 μm when the relative span factor of the droplet spectrum was reduced from 1.0 to 0.6. In the latter scenario, an increase from 63 to 67% of the volumetric proportion of droplets adhering to the wheat leaf was observed. Therefore, strategies for controlling the droplet size distribution may offer promising solutions for reducing adverse impact of spray applications on environment.