AUTHOR=Buchhart Claudia , Schmidhalter Urs 

TITLE=Daytime and seasonal reflectance of maize grown in varying compass directions

JOURNAL=Frontiers in Plant Science

VOLUME=Volume 13 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.1029612

DOI=10.3389/fpls.2022.1029612

ISSN=1664-462X

ABSTRACT=High temporal and spatial resolution is required to meet the challenges of changing plant characteristics over time. Solar radiation and reflectance of vegetation canopies vary with the time of day and growing season. Little is known regarding the interactions between daily and seasonally varying irradiation and reflectance of row-planted crops that can be grown in any compass direction. The spectral reflectance of maize grown in four compass directions was recorded across the entire life cycle through highly frequent drone-based multispectral sensing to determine biomass changes over time and make early yield predictions. Comparisons of information from spectral bands and indices indicated no differences among the four compass directions at the reproductive stage and only a few differences at the earlier vegetative growth stages. Spectral indices were closely related to the biomass and grain yield of maize grown in the four compass directions independent of the angle of solar radiation. There was no systematic influence of row orientation on the relationships between spectral data, biomass, and grain yield, except at the early growth stages. Spectral relationships to biomass at the reproductive stage varied in row directions with R2-values close to 0.9, already observed at early growth stages for the indices NDVI, SR, GCI, and GNDVI. The spectral relationships to yield were closer in individual compass directions, with R2-values varying between 0.8–0.9 for the best indices GCI and GNDV after BBCH 61. Overall, grain yield was slightly better predicted than biomass. A closer inspection of daytime changes indicated a diurnal trend with the lowest spectral values observed after midday, thus requiring standardization of flight timing during the day. Drone-assisted nadir-oriented spectral sensing could serve as a reference for terrestrial sensing and satellite-based reflectance sensing to quantitatively relate canopy reflectance to crop characteristics.