Effect of Adjuvant, Concentration and Water Type on the Droplet Size Characteristics in Agricultural Nozzles

Abstract

One of the goals of adding adjuvants to agricultural spray solutions is to enhance the droplet size characteristics of this spray. Droplet size, in turn, has an influence in the deposited spray quality, in addition to the drift and losses of spray to off-target places. The aim of this research was to evaluate the effect of adding adjuvants to two types of water from different sources on the droplet size characteristics. Two types of adjuvants were employed in the tests: the active substance content of the first adjuvant was a 50% aqueous solution of sodium salt of alkylbenzenesulfonic acid—10% (HY), whereas the second was from rapeseed oil (natural origin)—85% (OL). Both adjuvants were tested in two concentrations: the first was with the concentration recommended by the manufacturer (100%), whereas the second concentration was 50% of the recommended dose. Two types of water from different sources were used in the tests: the first was from a village in the eastern part of Poland (WS), whereas the second was tap water from the city of Lublin, Poland (WUP). D_v0.1, D_v0.5, or volume median diameter (VMD), D_v0.9, Sauter mean diameter (SMD), relative span (RS), and the droplet size distribution were measured and calculated as characteristics of the droplet size. Results showed that the source of water affected the influence of adding adjuvant to the spray solution. Water from the WS source with adjuvant resulted in a numerical decrease in the D_v0.5 values in the percentage of droplet size range below 150 µm, whereas water from the WUP source resulted in an increase in these values (except when adding the HY adjuvant at 50% concentration). Adjuvant concentration significantly (p < 0.05) influenced the features of D_v0.9, SMD, and RS. Adding the OL adjuvant type numerically decreased the percentage of droplet size below 150 µm, and the D_v0.5 values, but only when the WS water source was used.

1. Introduction

Adding adjuvants to spray solutions influences the droplet formation process and, ultimately, the produced droplet size. The droplet size itself has an effect on spray coverage, deposition, wetting, spreading, and drift. The aim of adding adjuvants to spray solutions is to enhance the pesticide, fungicide, insecticide, herbicide, and fertilizer application processes. Different types of adjuvants are available for employment in spray solutions, including surfactants, spreaders, stickers, deposition aids, activators, humectants, anti-foaming agents, wetting agents, and drift-reduction agents [1]. Liquid properties, in addition to leaf surface properties and other spraying parameters, are the main parameters affecting the contact angle and surface free energy, which in turn control the leaf surface wettability [2]. Adding adjuvants to the spray solution reduces the droplet surface tension [3,4,5,6,7,8], contact angle values [3,6,7] and pH values [3]. Adjuvant addition enhances spray deposition and electrical conductivity [4], and improves the control efficacy of pesticides [9]. Moreover, adding adjuvants results in a higher wetting surface area [5] and increases the density and viscosity of the spray solution [6]. The concentration of adjuvant within the spray solution affects different parameters. The researchers of [10], for example, state that the adjuvant concentration has important effects on the spray droplet. Accordingly, the surface tension decreases when the adjuvant concentration is increased, as affirmed in the work of [11]. In addition, they found that the conductivity and chargeability of the spray solution was enhanced as the adjuvant concentration increased (except for a “water only” treatment). In turn [12], suggests that using the appropriate adjuvant concentration would result in a better uniformity of spray coverage on both waxy and hairy leaf surfaces. They also indicated that increasing the adjuvant concentration improves the wetted area of droplets. A study by [13] notes that adjuvant concentration changes the dynamic evaporation of spray droplets; this outcome may depend on the adjuvant property.

Fine droplets can be expected when the surface tension of the droplets is reduced due to using adjuvants [10]. The researchers of [7] report a 33.5% reduction in the droplet size (D_v0.5) after adding adjuvant to the spray solution. Those of [14] also note that adding surfactant-based adjuvants to the spray solution results in a slight reduction in the droplet size. However, adjuvant types that generate oil-enhanced droplets within the spray solution (crop oils, petroleum oils, some water-insoluble emulsifiers, and surfactants) can unpredictably produce an increase in the droplets size [14]. In turn, the researchers of [15] show that using adjuvants of the oil-containing type results in the largest droplet size, while silicone surfactants and polymer-based adjuvants produce the smallest. Finally [16] indicate that adding adjuvants to the spray solution results in an increase in the volume median diameter of the droplets, and better homogeneity (relative span) of the droplet size.

The study of [17] saw an increase in the pinning probability and the pinned volume of the droplets after shattering on surfaces (on fat-hen or Teflon) due to the addition of surfactant. Accordingly, the effect of using adjuvants combined with using a low application rate and twin flat fan nozzles results in droplets with bigger diameter, while spraying insecticide via hollow cone nozzles without adjuvants results in a higher percentage of droplet drift [4]. Indeed, ref. [18] report a 63% decrease in drift when using adjuvants, depending on the combination of formulation/adjuvant, while the study results of [19] demonstrate a 39% reduction in the drift percentage. In turn, refs. [4,20] report similar results wherein the addition of adjuvant reduced the drift percentage, while [11] hold that the large values of surface tension for large droplets can be attributed to the cohesive forces within the solution molecules. Moreover, they see a difference in the surface tension of the water used in their study than that of normal water, and attribute this difference to the molecular size, entrained charge, and conductivity interactions of monosize droplets. Due to the fact that adding adjuvant increases the wetted area of spray [3,11,12], spray coverage can also be increased (depending on the surface of the target) when applying the spray with adjuvant.

Agricultural nozzles produce a wide spectrum of droplet sizes within their plumes [21]. The percentage of spray droplets having a diameter less than 100 μm is expected to increase when the spray droplet size is classified as fine spray. However, in some cases when using certain adjuvants types, a reduction in this percentage was noticed [10]. For example, ref. [22] report that using different types of adjuvants (high surfactant oil concentrate, nonionic surfactant, and acidifier and microemulsion drift-reduction agent) with glyphosate alone results in a decrease in the percentage of droplets <100 μm, compared with using the glyphosate solution. They also indicate that glyphosate with polymer solution results in the highest percentage of droplets <100 μm, compared with other solutions. The study of [23] indicates that the droplet size spectrum is influenced by the nozzle type. Pesticide drift is the main problem accompanying the pesticide application process, and fine droplet size is the main cause. Reducing the number of droplets of fine droplet size within the nozzle spray plume can reduce the possibility of spray drift. Adding adjuvants to the spray is one solution to this problem. However, their effect is unknown when they are mixed at lesser concentrations than that recommended by the manufacturer. In addition, the effect of adjuvant addition can be influenced by the type of water used to mix the adjuvant with the sprayed material. The objective of this study was to investigate the changes in the droplet size spectra due to the effect of adding two types of adjuvants with different concentrations to a spray solution consisting of water from two different sources.

2. Materials and Methods

The experiment was conducted with 12 treatments (2 × 3 × 2), composed of two types of adjuvants, with two concentrations in addition to the control treatment (no adjuvant), and two types of water. All combinations of tests were performed in three repetitions.

2.1. Adjuvants

The adjuvants used in the study were Hydrotek—manufactured by ELVITA Sp. z o.o. (Różewo, Poland) and OLEJAN 85 EC—manufactured by DANMAR Chemical Company (Łódź, Poland) (

Table 1. Information about the adjuvants used in the tests.

Trade Name	Active Substance Content	Composition	Concentration	Abbreviation
Hydrotek	50% aqueous solution of sodium salt of alkylbenzenesulfonic acid—10%	benzenesulfonic acids, C10-13 alkyl derivatives, sodium salts, alcohols C12-14, ethoxylated	0%, 50%, 100%	HY
OLEJAN 85 EC	rapeseed oil (natural origin)—85%	Alcohols, C12-14, ethoxylated	0%, 50%, 100%	OL

). Hydrotek is used as an additive to the spray solution to enhance wetting and adhesion. Its recommended dose is 50 mL per 100 L of spray solution, with a suggested dose of 0.15 L ha⁻¹ at in application rate of 250–300 L ha⁻¹. The manufacturer advises using Hydrotek with fungicides, insecticides, and herbicides (glyphosates) if the plant protection product (PPP) producer recommends the addition of a wetting agent with their product. OLEJAN 85 EC is a concentrate for making a water emulsion to enhance wetting and adhesion. The active substance of OLEJAN 85 EC is rapeseed oil from a natural origin, and it is applied with PPP and foliar fertilizers (if the producer recommends using a wetting agent). The suggested dose of OLEJAN 85 EC is 1.5 L ha⁻¹ in 200–300 L ha⁻¹ with PPP, and 1.0–1.5 L ha⁻¹ with foliar fertilizers.

The concentrations of adjuvants were chosen based on manufacturer label recommendations (

Table 2. Concentrations of adjuvants used in the study.

Adjuvants	Recommended Concentration (from Label)	Concentration
		0%	50%	100%
Hydrotek	50 mL per 100 L	Water only (control)	25 mL per 100 L	50 mL per 100 L
OLEJAN 85 EC	600 mL per 100 L *	Water only (control)	300 mL per 100 L	600 mL per 100 L

* The manufacturer recommended to use this adjuvant in a range of 200–300 L ha⁻¹ application rates; the 250 L ha⁻¹ application rate was chosen as a midpoint of this range.

). Two concentrations were used: the first was 100% (as stated in the label), and the second was 50% of the concentration stated on the label. The concentration 0% was considered as a “control” using water only.

2.2. Type of Water

The water types used in the research were from the water supply of two different locations in Lubelskie voivodship in Poland (

Table 3. The properties of water types used in the tests.

Water Source	Density (kg/m3)	Viscosity (Pa·s *)	pH	Hardness mg CaCO3/L (ppm)	Abbreviation
Sosnówka village	0.9992	831 × 10−6	8.44	Medium hard (225)	WS
Laboratory of the University of Life Sciences in Lublin	0.9998	889 × 10−6	7.42	Hard (518)	WUP

* Water temperature 21.5 °C, ppm—particles per million.

). The first water type was from the laboratory of the University of Life Sciences in Lublin, where the tests were carried out. The other water type was from a farm in Sosnówka village, Biała Podlaska region, Lublin Voivodeship, in Eastern Poland. The properties of water types used in the tests are shown in Table 3; these include density, viscosity, pH, and hardness. A glass hydrometer was employed to measure the density. Viscosity was measured with a rotational viscometer TQC model DV 1402 with a measuring range of 200–200,000 × 10⁻³ Pas. Measurements of pH, density, and hardness were made using an Extech EC 500 multifunction meter with pH measuring range of a 0–14, and water hardness measuring range of 0–999 mg/L. The water hardness categories were defined on the basis of [24], and defined as medium hard and hard.

2.3. Surface Tension

The surface tension was tested on the Drop Shape Analyzer device DSA30 (KRÜSS GmbH, Hamburg, Germany), using the pendant drop method. The pendant drop is a drop suspended from a needle in a bulk liquid or gaseous phase. The shape of the drop results from the relationship between the droplet volume, density, and surface tension. This method allows determining the surface tension of the liquid based on the shadow image of the pendant drop measured using drop shape analysis [25,26,27,28].

2.4. Measurement of Droplet Size Spectra

The nozzle model used in the study tests was the Universal Flat Fan Nozzle AP 120-03 from Agroplast Marcin Łopąg (Sawin, Poland). According to the manufacturer’s catalogue, the flow rate for this nozzle is 1.20 L/min at a spray pressure of 3 × 10⁻⁵ Pa. The droplet classification for this type of nozzle at 3 × 10⁻⁵ Pa pressure is a fine droplet. The spray solution was pressurized using compressed air in the spray tank; the pressure was kept at 3 × 10⁻⁵ Pa during the test with the help of a pressure regulator and pressure gauge. The spraying system components are shown in Figure 1.

A Sympatec GmbH-HELOS-VARIO/KR device (Sympatec GmbH, Clausthal-Zellerfeld, Germany) was employed to measure the droplet size characteristics and droplet size distribution of the spray plume. The device follows the physical principles of Laser Diffraction (LD), and the core of the measuring device contains a HELOS/R LD sensor. The device was positioned below the nozzle tip. The distance between the nozzle tip and the measurement zone was kept at 50 cm during the entire test, and the cross-sectional area of the spray plume at this position was analyzed. When the nozzle spray reaches the measurement zone, measuring began by means of the software (WINDOX 5.10) of the laser diffraction device. The nozzle was mounted inside a nozzle holder, and moved horizontally alongside its rail (right and left movement) by means of a DC servomotor. This was controlled through dedicated software with simple interface. Spraying the solution during sampling was controlled through a solenoid valve, which was managed by the same software that enabled nozzle movement.

The following parameters [29] were measured for the adjuvants at the determined concentrations and for both types of water: (1) D_v0.1, D_v0.5, or volume median diameter (VMD), and D_v0.9—these refer to the droplet size at which 10, 50, and 90% of the spray volume is comprised of droplets of smaller or equal size, respectively. (2) Sauter mean diameter (SMD)—this parameter describes the spray fineness with regard to surface area. It is defined by the droplet diameter, which has the same ratio between volume and surface area as the entire volume of all droplets to the complete surface area of all the droplets. (3) Relative span (RS) of the spray—as a non-dimensional parameter representing the homogeneity of the spray spectrum. Values of RS close to zero imply a more uniform spray spectrum. The RS was calculated as follows:

$$\mathrm{RS}=\frac{{\mathrm{D}}_{\mathrm{v}0.9}-{ \mathrm{D}}_{\mathrm{v} 0.1}}{{\mathrm{D}}_{\mathrm{v} 0.5}}$$

(1)

(4) Volumetric percentage of different droplets size ranges—this was measured within the following ranges: % ≤100 µm; 100–150 µm; 150–200 µm; 200–250 µm; 250–300 µm; 300–350 µm; 350–400 µm; 400–450 µm; 450–500 µm; 500–600 µm; 600–700 µm; 700–3500 µm.

2.5. Statistics

All datasets were submitted to statistical analysis using Statistica^®13.3 (Statsoft, Tulsa, OK, USA) assuming the significance level of α = 0.05. The treatments were analyzed by applying a 2 × 3 × 2 factorial complete randomized design (adjuvants type, concentration, water type) with at least three replications.

Since the examined variables were not subjected to the normal distribution (Shapiro–Wilk test, p < 0.05) and the attempts to apply data transformation did not yield the expected results, the non-parametric Mann–Whitney U test was applied to verify the significant influence of the water source and adjuvant factors on the examined features. The influence of the concentration factor was verified by the non-parametric Kruskal–Wallis test. In this case, a post-hoc analysis of multiple comparisons was also performed, which made it possible to determine statistically significant differences.

3. Results and Discussion

Results of the effect of the studied factors on the surface tension are shown in

Table 4. Effect of water type, adjuvant type, and concentration on the surface tension.

Water Source	Adjuvant/Concentration	Droplet Volume (μL)	Surface Tension (mN/m)			Standard Deviation
			Mean	Min.	Max.
WS	−/0% (control)	28	71.56	70.34	72.39	0.53
	HY/50%	16	51.45	45.81	55.85	2.52
	HY/100%	14	36.26	34.16	38.45	1.23
	OL/50%	16	52.35	47.30	58.19	2.84
	OL/100%	14	36.71	34.64	39.90	1.53
WUP	−/0% (control)	28	73.41	71.60	75.04	0.66
	HY/50%	16	53.78	48.56	58.03	2.46
	HY/100%	14	36.87	33.43	40.24	1.96
	OL/50%	16	54.27	48.56	61.77	3.13
	OL/100%	14	37.19	33.63	41.15	2.01

. Application of both adjuvant types resulted in a decrease in surface tension. This reduction was to almost half of its original value (control water sample without adjuvants) when adding the recommended concentration (100%) of the adjuvants. This trend was observed for both types of adjuvants, and for both types of water. Decreasing the value of surface tension would improve the deposition and wetted area, and the latter would enhance the spray coverage on the target, as reported in [11]. There was a slight numerical difference in the surface tension values between the two types of water, with or without adjuvants. The results of the droplet size characteristics are shown in

Table 5. Effect of water type, adjuvant type, and concentration on droplet size characteristics (mean ± standard deviation).

Water Source	Adjuvant/Concentration	Dv0.1 (μm)	Dv0.5 (μm)	Dv0.9 (μm)	SMD (μm)	RS (-)
WS	−/0% (control)	97.29 ± 15.32	196.27 ± 4.25	301.06 ± 4.86	127.03 ± 8.25	1.04 ± 0.08
	HY/50%	73.35 ± 6.29	180.24 ± 2.47	351.78 ± 8.32	125.71 ± 14.50	1.54 ± 0.02
	HY/100%	77.21 ± 0.29	184.97 ± 2.77	359.08 ± 5.82	134.12 ± 0.91	1.52 ± 0.01
	OL/50%	109.95 ± 0.34	191.72 ± 1.48	333.46 ± 3.45	164.77 ± 0.43	1.17 ± 0.02
	OL/100%	82.38 ± 2.96	190.34 ± 5.58	391.75 ± 9.91	133.51 ± 12.17	1.63 ± 0.02
WUP	−/0% (control)	64.76 ± 2.02	186.78 ± 3.97	302.09 ± 18.69	116.35 ± 6.88	1.27 ± 0.06
	HY/50%	99.87 ± 2.81	185.62 ± 2.53	366.58 ± 11.76	149.34 ± 14.90	1.44 ± 0.04
	HY/100%	93.40 ± 2.10	221.07 ± 4.41	391.59 ± 7.40	165.91 ± 4.39	1.35 ± 0.04
	OL/50%	96.81 ± 0.61	197.34 ± 0.50	373.21 ± 10.08	118.34 ± 1.45	1.40 ± 0.06
	OL/100%	101.92 ± 3.20	198.21 ± 0.94	359.23 ± 2.85	134.39 ± 13.84	1.30 ± 0.04

. Numerically, there was a slight decrease in the values of D_v0.5 after adding both types of adjuvants (especially the HY adjuvant) to the WS-type water, when compared to the control treatment (without adjuvant). Although this decrease was small, it may be important because it occurs on droplets below 200 μm size. This droplet size is responsible for spray drift. The opposite trend was observed when adding both types of adjuvant to the WUP-type water, except when adding the HY adjuvant with 50% concentration—where the D_v0.5 slightly decreased. It is known that decreasing the surface tension of a certain spray results in a decrease in the droplet size (D_v0.5) of this spray. Here, the decrease in surface tension contributes to the reduction in the droplet size. At the same time, increasing the density of the liquid causes the formation of larger droplets. These outcomes demonstrate the variable influence of the adjuvant on the drop formation [6,7]. In examining the data listed in Table 4, it is noticeable that there were decreases in surface tension of 29 and 28% when adding HY and OL adjuvants (with a concentration of 50%), respectively, to the WS water type, whereas decreases of 50 and 49% were observed when HY and OL adjuvants were added (with a concentration of 100%), respectively, to the WS water type. A similar percent decrease in the surface tension values resulted from using the WUP water type.

When the concentration of 50 or 100% was employed, the differences in the percent decrease in the surface tension values were not reflected in the droplet size (D_v0.5) results, as shown in Table 5. Here, we observed a noticeable decrease in the values of D_v0.5 when both types of adjuvants with 100% concentration were added, as compared to the 50% concentration, except for OL in the WS water type, as D_v0.5 was found to be less sensitive to the variation in the OL additive. This type of adjuvant changes the fine droplets in the Dv_0.1 range by emulsifying the liquid with oil, which increases their diameter and stabilizes D_v0.5 However, this tendency was reflected in the results of SMD values, which are relevant in applications where the active surface area is important. When we added an oil adjuvant to the working liquid, the drops were found to be formed closer to the nozzle outlet, which resulted in the formation of drops of larger size and uniform spraying of the liquid [10]. In the real world, adjuvant addition should lower SMD, and this outcome should increase the amount of low range fractions of 0–150 μm. In this case, the better results were obtained if HY at the concentration of 50% was used. The values of relative span (RS), which is an indicator of the homogeneity of spray droplet spectra, were higher after adding the adjuvants for both types of water, as compared to the control water sample. As values of RS closer to zero indicate better homogeneity of spray droplet, adding adjuvants resulted in an adverse effect on this indicator for both types of water. The reason for this is that the gap between D_v0.9 and D_v0.1 enlarges due to the changes in the droplets’ size in the spray plume after adjuvant. Adjuvant concentration was the only factor significantly (p < 0.05) influencing the features of D_v0.9, SMD, and RS. The other two factors (water source, adjuvant type) did not significantly affect the examined features (p > 0.05).

Table 6. Results of the post-hoc multiple comparison test for the concentration factor.

Trait	Concentration	0%	50%	100%
Dv0.9	0%		0.0016 *	0.0000 *
	50%	0.0016		0.4550
	100%	0.0000	0.4550
SMD	0%		0.1317	0.0124 *
	50%	0.1317		1.0000
	100%	0.0124 *	1.0000
RS	0%		0.0053 *	0.0005 *
	50%	0.0053 *		0.9989
	100%	0.0005 *	0.9989

* Significant at p < 0.05.

presents the results of post-hoc multiple comparison tests for the concentration factor and traits D_v0.9, SMD, and RS. For feature D_v0.9, no statistically significant differences were found between the 50 and 100% concentrations (Table 6, p > 0.05). In contrast, the D_v0.9 values obtained for the 50 and 100% concentrations differed significantly in relation to the control (0%). In the case of the SMD feature, a statistically significant difference was found between the control group (0%) and the concentration at the level of 100%. Similar results were seen in [9,22] (Table 6, p < 0.05). For the RS feature, no statistically significant differences were found between the 50 and 100% concentrations (Table 6, p > 0.05). However, the RS value obtained for the 50 and 100% concentrations differed significantly from that of the control group (0%).

Data presented in

Table 7. Effect of water type, adjuvant type, and concentration on droplet size distribution.

Water Source	Adjuvant/Concentration	Proportion of Droplets in Each Fraction (%)
		0–100 μm	100–150 μm	150–200 μm	200–250 μm	250–300 μm	300–350 μm	350–400 μm	400–450 μm	450–500 μm	500–600 μm	600–700 μm	700–3500 μm
WS	−/0% (control)	18.94	21.43	16.11	10.84	11.22	10.34	7.27	2.90	0.50	0.20	0.13	0.06
	HY/50%	21.37	24.44	17.68	11.11	6.99	4.80	3.73	9.02	2.46	2.90	1.10	0.57
	HY/100%	20.79	23.84	17.70	11.32	7.08	4.92	3.87	2.98	2.57	8.09	1.33	0.56
	OL/50%	11.92	18.12	21.35	19.69	13.16	6.99	3.96	2.06	1.29	0.86	0.17	0.44
	OL/100%	15.73	21.10	19.56	14.40	9.15	5.73	4.06	2.85	2.33	2.75	1.34	0.99
WUP	−/0% (control)	22.54	22.69	16.08	10.69	9.33	7.72	5.35	2.93	1.71	0.63	0.23	0.09
	HY/50%	15.95	18.55	19.63	16.34	10.72	6.51	4.39	2.83	2.14	1.87	0.64	0.54
	HY/100%	17.27	22.46	16.55	10.26	6.51	5.11	4.59	4.09	3.84	5.32	2.39	1.62
	OL/50%	13.73	15.58	20.34	18.17	12.25	7.34	4.80	2.93	2.11	1.57	0.48	0.68
	OL/100%	12.85	15.99	20.44	18.57	12.76	7.64	4.95	2.98	2.13	1.52	0.14	0.03

indicate a decrease in the percentage of droplet size fraction of 0–100 μm when the OL adjuvant was added to the spray solution with the WS water type. The reduction was from 18.9% for the “control” (water only) treatment, to 11.9 and 15.7% upon using 50% and 100% concentrations, respectively. These results are in agreement with the findings of [10,20]. The opposite trend was observed when adding HY adjuvant. This effect would be lower if we accumulate the 0–100 μm fraction with the 100–150 μm fraction, since both fractions are responsible for spray drift. In the table, it is noticeable that adding the OL adjuvant at100% concentration resulted in a higher percentage of the 0–150 μm fraction (accumulated) than in using the 50% concentration. For the WUP water type, the addition of both types of adjuvants with both concentrations resulted in a decrease in the percentage of the 0–100 μm fraction of droplet size. However, the OL adjuvant showed a greater decrease in this fraction. Nearly the same trend was observed when accumulating the 0–100 μm and 100–150 μm fractions of droplet size. The coarse droplet size (≥500 μm) fractions, which can be responsible for the losses of the spray solution to the ground, increased after adding both types of adjuvants to the two concentrations, and for both water types. In the case of fractions 150–200 μm and 200–250 μm, application of both adjuvants increased the number of droplets in the proportion of spray, independent of the adjuvant type and water source. This would have a positive effect on the number of droplets being in contact with the plant leaf surface during spraying, hence increasing the efficiency of spraying.

Table 8. Effect of water source, type of adjuvant, and its concentration on drop fraction (p-value).

Sources of Variation	0–100	100–150	150–200	200–250	250–300	300–350	350–400	400–450	450–500	500–600	600–700	700–3500
water source	0.56	0.56	0.93	0.48	0.30	0.93	0.20	0.62	0.59	0.68	0.42	0.60
adjuvant	*	*	*	*	*	*	*	*	*	*	*	*
concentration	*	*	*	*	*	*	*	0.55	*	*	*	*

* p < 0.05.

presents the results of non-parametric tests (probability p-value) verifying the significant influence of the water source, type of adjuvant, and its concentration on the droplet size fractions. The table reveals that droplet size fractions are not significantly differentiated between different water sources (p > 0.05). In contrast, the type of adjuvant and concentration are factors that significantly differentiate the droplet size fractions in all ranges (Table 8, p < 0.05), except for the 400–450 μm fraction (concentration, p > 0.05).

Adding the OL adjuvant to the WUP water type yielded the expected results of increasing the D_v0.5 and decreasing the percentage of droplets sized below 100 μm and 100–150 μm, compared to the control water sample, as confirmed in [4]. However, adding this type of adjuvant (OL) to the WS water type (from Sosnówka village) showed the opposite tendency by resulting in a decrease in D_v0.5 and an increase in the percentage of droplets sized below 100 μm. When HY was applied as an adjuvant, a more intensive increase in the proportion of droplets in the 0–250 μm fractions was observed if WS water was used in the experiment. The WUP water application yielded significant differences in droplet proportion depending on the fractions. This effect was noticeable in the 0–150 μm droplet size and resulted in a decrease, compared to the control water sample; however, on analyzing fractions between 150 and 250 μm, an increase in droplet proportion occurred. In most cases, addition of adjuvants to both WS and WUP water increased the proportion of droplets in the fractions in the range between 150 and 300 μm, but the most significant differences were observed when OL was applied. The outcome of this research is beneficial in enhancing the efficiency and effectiveness of the pesticide application process, by reducing drift, and by improving the deposition and coverage of sprays on targets. However, it is recommended to further investigate the outcomes of this research when using plant protection products instead of water. Moreover, it is also recommended to investigate the effect of atmospheric conditions (ambient temperature and relative humidity), since they may influence the work of adjuvants that are different in their composition, as stated in [20]. Finally, it is recommended to study the spreading behavior of the spray droplets with regard to the studied adjuvants with plant protection products.

4. Conclusions

• The presented results may constitute the basis for the continuation of research work carried out on a larger, more practical scale under field conditions.
• Water source affected the performance of the added adjuvants, especially that of the type from Sosnówka village, Poland (WS).
• Adjuvant OL concentration significantly affected the D_v0.1, D_v0.9, SMD, and RS spray features. However, it did not affect the D_v0.5 values because this fraction range is the least sensitive to any changes in the other droplet fractions.
• The OL adjuvant type could be successfully applied in agricultural sprayers by increasing D_v0.5 and decreasing the percentage of droplet size below 150 μm, although only when using the tap water from the WUP source.
• The possibility of continuing this research should be considered with the use of portable research devices and field devices, in addition to other types of adjuvants, to verify whether the results will be similar and whether it will be possible to use these in practical agricultural applications.
• The authors’ recommendation is to use OL adjuvants, as these were found in practice to reduce the occurrence of fine droplets susceptible to the drift effect.