Subsoiling (SS) is an important technology in conservation tillage, but soil-disturbance characteristics in the SS are rarely described. Research on soil-disturbance characteristics during SS is conducive to the design and optimization of subsoilers, which provides a basis for reducing draft force and energy consumption. This study conducted SS experiments at five different tillage depths in the field with a specific field in situ test-rig facility, and in situ videotaping was made from five positions during SS. The microrelief test, draft force test, disturbance cross-section test and disturbance process analysis were conducted after SS. The results showed that draft force increased with tillage depth as a quadratic function. Soil displacement parameters and soil crack parameters extracted from the video of SS were significantly correlated with tillage depth, which could be used for a quantitative description of the paddy soil-disturbance characteristics. Cross-sectional area showed a trend of “increasing then decreasing” with increasing tillage depth, reaching a maximum at a tillage depth of 20 cm. When the tillage depth was greater than 20 cm, the bottom of the disturbing boundary formed a “mole cavity”. Fallback rate was used to describe the change in disturbed height or width during and after SS, which exceeded 100% at maximum. The surface roughness of microrelief and the size of the average clods reached the maximum at tillage depth of 20 cm. Considering the shallow cultivation layer of paddy soil in rice–wheat rotation, the recommended tillage depth of 20 cm could achieve maximum soil disturbance and minimum energy consumed.

Subsoiling is an important technology in conservation tillage. The disturbance characteristics of paddy soil were simulated by smoothed particle hydrodynamics (SPH) in this paper in order to explore the optimal tillage depth of paddy soil in a rice–wheat rotation area. Firstly, a subsoiling experiment with five tillage depths was carried out by a self-made multi-functional in situ test-rig facility. Then, a three-layer-soil subsoiling model of a cultivated layer, plow pan, and subsoil layer was established based on the SPH method. Finally, the soil disturbance characteristics were analyzed from macroscopic and microscopic perspectives. The results showed that the average draft force in simulation was consistently lower than in the field, with a maximum error of 18.71%, and the field draft force fluctuated greatly. The soil block above the tine was not lifted up as a big block but broken into many small soil blocks and then lifted up, resulting in different displacements of the soil particles, but the relative position was unchanged from top to bottom. The particle displacements were concentrated above the tine, the stress was concentrated around the tine, while the velocity and acceleration were closely attached to the subsoiler. A “mole cavity” at 25 and 30 cm tillage depths existed at the bottom of the disturbance, which was consistent with the finding in the field. The disturbance area and specific draft were maximum and minimum at 20 cm tillage depth, respectively. These findings suggest that the optimal tillage depth was 20 cm for the rice–wheat rotation area. The results of the analysis provide a theoretical basis for the optimal design of subsequent subsoiling.

Subsoiling is an important method in conservation tillage, but it requires a lot of energy. In order to explore the energy distribution of tillage-induced soil fragmentation, soil tillage fragmentation efficiency was proposed to represent the ratio between energy consumed by soil fragmentation and energy input by tillage. A self-made multi-functional in situ test rig facility was used. The energy consumed by soil fragmentation was calculated by multiplying total area of soil fragmentation by specific surface contacting energy. The total area of soil fragmentation in the field was quantified by combining three complementary techniques, the sieve method for small aggregates (∅<64 mm), the camera method for large aggregates (∅≥64 mm), and the clone powder pouring method. The specific surface contacting energy was obtained by falling weight test. In addition, a digital cone-penetrometer was used to obtain contour of soil penetration resistance and a pin-type profilometer was used to calculate the cross-sectional area. The results showed that the draft force and specific draft increased with increasing tillage depth, reaching a maximum at a tillage depth of 20 cm. The specific surface contacting energy increased exponentially with soil depth. The cross-sectional area, total area of soil fragmentation and soil tillage fragmentation efficiency showed a trend of first increasing and then decreasing with an increase in the tillage depth, and reached a maximum at a tillage depth of 20 cm. The contour of soil penetration resistance before the experiment showed that the plow pan was located at a depth of about 15 cm.

The atomization performance of the nozzle is a critical factor influencing the pesticide application efficiency and drift behavior of agricultural unmanned aerial spraying systems (UASSs). However, the underlying atomization mechanisms of such nozzles have not yet been fully elucidated. In this study, a Particle Image Velocimetry (PIV) system was employed to evaluate the liquid sheet breakup mode, breakup length, droplet size distribution, and velocity distribution of a fan-shaped nozzle used in UASSs. Experiments were conducted under a series of spray pressures (ranging from 0.10 to 0.50 MPa, with an increment of 0.05 MPa) using sodium dodecylbenzenesulfonate (SDS) surfactant solutions at four concentrations (0%, 0.2%, 0.5%, and 1.0%). The results demonstrated that both the SDS surfactant and spray pressure significantly influenced the liquid sheet breakup process and atomization behavior. High concentrations of surfactant solution had a pronounced effect on the surface tension of the spraying liquid, delaying the onset of liquid sheet breakup, enlarging the overall droplet size distribution, and reducing the droplet velocity components along the X-axis and Y-axis. Conversely, higher spray pressures facilitated liquid sheet breakup, decreased the overall droplet size, and increased the droplet velocity distribution. This study provides fundamental experimental data for quantifying the effects of solution surface tension and spray pressure on the atomization performance of fan-shaped nozzles. These data provide systematic support for the evaluation of nozzle atomization performance.