View-dependent canopy gap fraction is a directional descriptor of canopy openness that provides structural information for characterizing fruit-tree canopy heterogeneity. However, existing LiDAR-based canopy characterization methods are limited in their stability for characterizing zone-specific variations in canopy occlusion. This study proposes a LiDAR point-cloud column projection method for estimating zone-specific view-dependent canopy gap fraction of fruit tree canopies. A flash LiDAR sensor and an RGB camera were used to acquire paired point-cloud and image data from a simulated fruit tree and real peach trees under matched viewing directions and consistent region-of-interest constraints. Image-derived canopy gap fraction, calculated from the blue-cloth background area in each 3 × 3 subregion, was used as the reference value. The proposed column projection method was compared with a regional volumetric occupancy method and a regional two-dimensional projection coverage method. Under the indoor method-development conditions, using 88 paired frames, the proposed method achieved a mean absolute error of 8.59%, a Pearson correlation coefficient of 0.925, and a Spearman rank correlation coefficient of 0.914 relative to the image-derived reference values. In the preliminary semi-controlled outdoor evaluation using eight paired real-tree samples, the method achieved a mean absolute error of 10.48% and showed lower numerical errors and systematic bias than the two baseline methods. These results indicate that the proposed method can provide zone-specific view-dependent canopy gap fraction estimates that are more consistent with image-derived reference values under the tested conditions.

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.