Estimating vertical plant area density profile and growth parameters of a wheat canopy at different growth stages using three-dimensional portable lidar imaging

Vertical plant area density profiles of wheat (Triticum aestivum L.) canopy at different growth stages (tillering, stem elongation, flowering, and ripening stages) were estimated using high-resolution portable scanning lidar based on the voxel-based canopy profiling method. The canopy was scanned three-dimensionally by laser beams emitted from several measuring points surrounding the canopy. At the ripening stage, the central azimuth angle was inclined about 23∘ to the row direction to avoid obstruction of the beam into the lower canopy by the upper part. Plant area density profiles were estimated, with root mean square errors of 0.28–0.79 m2 m−3 at each growth stage and of 0.45 m2 m−3 across all growth stages. Plant area index was also estimated, with absolute errors of 4.7%–7.7% at each growth stage and of 6.1% across all growth stages. Based on lidar-derived plant area density, the area of each type of organ (stem, leaves, ears) per unit ground area was related to the actual dry weight of each organ type, and regression equations were obtained. The standard errors of the equations were 4.1 g m−2 for ears and 26.6 g m−2 for stems and leaves. Based on these equations, the estimated total dry weight was from 63.3 to 279.4 g m−2 for ears and from 35.8 to 375.3 g m−2 for stems and leaves across the growth stages. Based on the estimated dry weight at ripening and the ratio of carbon to dry weight in wheat plants, the carbon stocks were 76.3 g C m−2 for grain, 225.0 g C m−2 for aboveground residue, and 301.3 g C m−2 for all aboveground organs.