Effect of operating parameters of hydraulic nozzle on spray droplet characteristics

Introduction

The spray characteristics of agricultural spray nozzles are important criteria in the application of herbicide because of their ultimate effect on the efficiency of the herbicide application process. Droplet size and velocity affect the structure of the spray deposits and the driftability of the droplets. Hence, the ideal nozzle-pressure combination will maximise spray efficiency for depositing and transferring a lethal dose to the target, whilst minimising offtarget losses. The spray characteristics influencing the efficiency of the herbicide application process are the droplet size and uniformity pattern, the volume distribution pattern, the spray structure and the structure of individual droplets (Miller & Butler Ellis, 2000) [7] . The issue of weeds and the methods used to control them has been a concern for farmers since the early days of agriculture. Over time, traditional labor-intensive methods of weed control have been replaced by more advanced techniques such as cultural, mechanical, chemical, and biological methods. Among these methods, chemical weed control has become popular due to the growing scarcity of labor and the increasing cost of manual weeding. Chemical weed control is favored for its cost-effectiveness and higher efficiency in controlling weeds (Choudhury et al., 2016) [2] . Herbicides are chemicals specifically designed to kill or control unwanted plants, or weeds, in both cropping and non-cropping situations. The effectiveness of herbicides and the tolerance of crops to them depend on the sensitivity of the weed species to the herbicide and the size of the weed or crop at the time of application. To ensure successful use of herbicides, accurate and uniform application is crucial (Miller and Bellinder, 2001) [8] . In agriculture, herbicides are applied before planting, after emergence, or post-emergence, depending on the specific crop and weed situation in the field. Various methods can be used to apply herbicides, including boom sprayers, aerial sprayers, misters, blanket wipers, rope wick applicators, weed seekers, backpack sprayers, and broadcasting of granular formulations (Peltzer, 2016; Choudhury et al., 2016) [11,2] . The nozzle is a critical component of the spraying system as it is responsible for atomizing the liquid herbicide. Using a single nozzle lance for herbicide application can make the spraying operation complex and challenging, as it can be difficult to achieve a straight swath with proper overlapping. To achieve optimal spray efficiency, it is crucial to find the perfect combination of nozzle pressure. This combination should aim to maximize the deposition of the spray and ensure a lethal dose is delivered to the intended target. At the same time, it is important to minimize any residues and losses that may occur off-target, such as spray drift and user exposure (Smith et al., 2000; Nuyttens et al., 2007; Nuyttens et al., 2009a) [16,9,10] . Various spray parameters, including droplet size and velocity distribution, spray pattern, entrained air characteristics, spray sheet structure, and individual droplet structure, play a significant role in determining the efficiency of the spraying system (Miller and Butler Ellis, 2000) [7] . Therefore, it is crucial to carefully consider all these factors and select the appropriate nozzle with the correct operational parameters for successful spraying operations.

Materials and Methods

Selection of hydraulic nozzles and spray operating pressures

Nozzle selection is the most important decision. The selected nozzle should develop desired spray pattern (Klein and Kruger, 2011; Sumner, 2012) [5,17] . The proper selection of a nozzle type and size is essential for effective herbicide application. A nozzle breaks the spray liquid into droplets to form a spray pattern and simultaneously propel the droplets in proper direction. It also determines the amount of spray volume at particular operating pressure, travel speed and spacing (Grisso et al., 2013; Slocombe and Sharda, 2015) [4,15] . For investigation of application on herbicide, four popular and commercially available hydraulic nozzles i.e. N1-Hollow cone HCN/PB, N2-Flat fan XLCC/900, N3-Flood type XLP/WP40 and N4-Flat fan F 110/16/3 (American Spring and Pressing Works Pvt. Ltd., Mumbai, MH, India) were selected Fig. 1. The specifications of selected nozzles are given in Table 1. The operating pressure required for spraying of herbicide by standard nozzle ranged from 100 to 400 kPa (Matthews, Bateman, and Miller 2014; Grisso, et al. 2019). [6,3]

Measurement of uniformity of spray transverse distribution

The uniformity of transverse distribution of the spray is calculated by coefficient of variation (CV). The lower value of the CV represents better uniformity of spray in transverse direction for a particular nozzle. The spray distribution pattern was measured for four different types of nozzles at different operating pressures and heights using the standard spray patternator (Sirmour et al. 2019) [13] . The nozzle was mounted at a height between 250 mm to 450 mm so that the sprayed liquid could be projected towards the patternator. The variation in collected spray liquid at each individual channel on the spray patternator was expressed by the coefficient of variation (CV) (Sirmour et al. 2019) [14] . The same procedure was repeated to determine the coefficients of variation of spray distribution of selected hydraulic nozzles at different operating pressures. The different dependent and independent parameters studied in the patternator test of all the four nozzles are presented in Table 1 and the treatments on uniformity of spray pattern are presented in Table 2.

Spray Particle Size Measurements

A variety of different particle sizing techniques have been used for the characterization of agrochemical sprays in the past. These vary from those based on intrusive collection methods, to imaging techniques and those using laser light scattering or absorption. Of those available, laser diffraction provides a flexible and rapid method for the assessment of the delivered particle size. The Malvern Particle Analyzer, which is considered a spatial sampling device, utilizes the fact that a spray drop will cause laser light to scatter through an angle dependent on the diameter of the drop (Sirmour et al. 2019) [13] . The laser diffraction technique was used to measure VMD of the liquid solutions using particle laser analysis system (Sehsah and Kleisinger 2009) [12] . The setup of system laser diffraction (Spraytec, Malvern P Analytical Ltd., Malvern, United Kingdom; Range =0.1-2000 µm, Precision/Repeatability= > ±1%) is shown in Figure 1.

Conclusion

In laboratory testing, N1-Hollow cone (HCN/PB), N2-Flat fan (XLCC/900), N3 -Flood type (XLP/WP40

References

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