Abstract
Unmanned aerial vehicle (UAV) technology is an emerging powerful approach for high-throughput plant phenotyping field-grown crops. Switchgrass (Panicum virgatum L.) is a lignocellulosic bioenergy crop for which studies on yield, sustainability, and biofuel traits are performed. In this study, we exploited UAV-based imagery (LiDAR and multispectral approaches) to measure plant height, perimeter, and biomass yield in field-grown switchgrass in order to make predictions on bioenergy traits. Manual ground truth measurements validated the automated UAV results. We found UAV-based plant height and perimeter measurements were highly correlated and consistent with the manual measurements (r = 0.93, p < 0.001). Furthermore, we found that phenotyping parameters can significantly improve the natural saturation of the spectral index of the optical image for detecting high-density plantings. Combining plant canopy height (CH) and canopy perimeter (CP) parameters with spectral index (SI), we developed a robust and standardized biomass yield model [biomass = (m × SI) × CP × CH] where the m is an SI-sensitive coefficient linearly varying with the plant phenological changing stage. The biomass yield estimates obtained from this model were strongly correlated with manual measurements (r = 0.90, p < 0.001). Taking together, our results provide insights into the capacity of UAV-based remote sensing for switchgrass high-throughput phenotyping in the field, which will be useful for breeding and cultivar development.
Highlights
Switchgrass (Panicum virgatum L.) is a native North America prairie grass that has been studied as a potential bioenergy crop in the United States and Europe since the mid-1980s (Lewandowski et al, 2003)
We applied the programming process to the light detection and ranging (LiDAR) point clouds collected from early peak season (Figure 5A) to the end-of-season (Figures 5B,C) for determining switchgrass phenotyping parameters including plant canopy height and perimeter
As for biomass modeling based on a pixel cell, we suggest using a highly related function for converting from plant canopy coverage areas (CAs) in the pixel cell to plant perimeter, which is developed based on Unmanned aerial vehicle (UAV) phenotyping measurements in the switchgrass field (i.e., canopy perimeter (CP) = 3.6789 × CA0.4892, r2 = 0.998; Figure 9)
Summary
Switchgrass (Panicum virgatum L.) is a native North America prairie grass that has been studied as a potential bioenergy crop in the United States and Europe since the mid-1980s (Lewandowski et al, 2003) It is a perennial grass, with C4 metabolism, which is adapted to cultivation in much of the eastern United States and similar regions requiring low agronomic inputs (Vogel, 2004; Bouton, 2007; Schmer et al, 2008). Switchgrass is highly self-incompatible, and its reproductive structures consist of a diffuse panicle arranged at the end of long branches (Barnes et al, 1995; Vogel, 2004) It produces high aboveground biomass each growing season as well as high lignin and cellulose content in cell walls (Vogel, 2004).
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