The pulse-width modulation (PWM) variable spray system is the most widely used variable spray system in the world at present, which has the characteristics of a fast response, large flow adjustment range, and good atomization. Recently, the pressure fluctuation and droplet deposition uniformity of the PWM variable spray system caused by the intermittent spray mode of the nozzle have attracted more and more attention. In this study, a method for eliminating the inhomogeneity of ground deposition in low-frequency PWM variable sprays based on a staggered-phase drive mode was proposed, and a PWM variable spray system was built. The experimental results indicated that the pressure fluctuation amplitude upstream of the nozzle of the PWM variable spray system with the staggered-phase drive was reduced by 40.91%, and the dispersion rate of the pressure fluctuation was reduced by 62.78% (the initial pressure was 0.3 MPa, solenoid valve frequency was 5 Hz, and duty cycle was 50%). The PWM control parameters had a significant effect on the upstream pressure fluctuation (initial pressure > duty cycle > frequency). The droplet spectrum relative span of the staggered phased PWM variable spray system decreased by 24.83%, the coefficient of variation of the droplet particle size decreased by 4.40%, the particle size was more uniform, and the atomization effect was improved. The average deposition of droplets in the forward direction driven by the staggered phase was 4.87% greater than that in the same phase, and the variation rate decreased by 20.87%. The average deposition amount increased, and the deposition became more uniform. Staggered-phase spray control could effectively reduce the inhomogeneity of deposition in low-frequency PWM intermittent spraying. This research provides strong technical support for a precision variable spraying effect and droplet drift prevention.

This paper studied the atomization characteristics of different spray nozzles under the spot spraying method and designed a test system for the atomization characteristics. First, the effective spray height range was determined based on the effective droplet size of 106–403 μm, the spray height of 200–500 mm, the operating speed of 0.5–1 m/s, and the droplet size requirements. The effective height ranges of the HVV25-02, HVV40-02, and HVV50-02 nozzles are 277–500 mm, 200–426 mm, and 200–266 mm, respectively. Second, the influences of pressure, the opening time of the solenoid valve, and the nozzle aperture on the atomization characteristics were studied through experiment. The experiment was repeated three times, with 10,000 points monitored each time. The test results show that the droplet size of spot spraying decreases with the increase in pressure, while the droplet velocity and droplet distribution relative span have no correlation with pressure. With the increase in the opening time of the solenoid valve, the droplet size does not change regularly, the droplet velocity generally shows an upward trend, and the droplet distribution relative span (RS) value decreases gradually. With the increase in the nozzle aperture, both droplet size and droplet velocity increase, and the distribution span shows a trend of first increasing and then decreasing. The droplet velocity of spot spraying is 4.1 m/s lower than that of continuous spraying, on average, and the droplet distribution relative span value is 2.2 higher than that of continuous spraying. This research can provide a basis and reference for the selection of appropriate spot spraying operation parameters.

Liquid mulch, as a spray-applied film-forming material, has considerable potential for agricultural mulching and soil environmental regulation. However, how liquid mulch spraying parameters affect headspace methyl isothiocyanate (MITC) concentrations remains unclear. The objective of this study was to quantify the effects of nozzle type and spray pressure on the spraying characteristics of liquid mulch and headspace MITC concentration responses and to examine the relationships among measured spraying characteristics, calculated theoretical equivalent film thickness, and AUC₄–₂₄ under controlled laboratory conditions. Three standard flat-fan nozzles (VP110-03, VP110-04, and VP110-05) were evaluated at spray pressures of 0.3, 0.4, and 0.5 MPa using a full factorial design. Soil-column incubation experiments and atomization characterization tests were conducted to investigate the effects of different spraying parameters on headspace MITC concentrations, AUC₄–₂₄, droplet size, droplet velocity, and theoretical equivalent film thickness. The results showed that the AUC₄–₂₄ values of all liquid mulch treatments were lower than that of the unsprayed control, ranging from 1585.32 to 2073.42 mg·h·m⁻³, with relative reductions of 53.16–64.19%. Dv_0.5 showed a weak and nonsignificant negative correlation with AUC₄–₂₄ (r = −0.235, p = 0.543), while mean droplet velocity exhibited a moderate but nonsignificant negative correlation with AUC₄–₂₄ (r = −0.568, p = 0.111). Theoretical equivalent film thickness showed the strongest negative association with AUC₄–₂₄ (r = −0.691, p = 0.039). The piecewise model showed that the relative reduction in AUC₄–₂₄ increased with theoretical equivalent film thickness at lower thicknesses and approached a plateau of 60.64% above an estimated breakpoint of 0.190 mm. Under the present laboratory conditions, a theoretical equivalent film thickness of approximately 0.20 mm may be considered a preliminary reference value. These findings provide a laboratory basis for further evaluating nozzle–pressure combinations, liquid mulch application rates, and suitable theoretical equivalent film-thickness ranges under field conditions.