Winter wheat light interception measured with a quantum sensor and images

Light interception (LI) measurements are essential for modeling crop biomass and grain yield. Canopy LI is often measured with linear quantum sensors, but the need for unobstructed sunlight near solar noon can make field measurements impractical. We aimed to evaluate the use of the fraction of green canopy cover (FGCC) as a surrogate for LI in winter wheat (Triticum aestivum L.) canopies. A linear quantum sensor and a camera were used to collect 930 observations during the 2021 growing season across three locations in Kansas. Images were analyzed with the Canopeo application. The quantum sensor was also used to estimate the LI and leaf area index (LAI) in different canopy strata. Growing season shoot dry biomass was modeled with LI values from images and the quantum sensor. The LI estimated by the quantum sensor and images resulted in a strong positive linear correlation (r = 0.97). During the vegetative stages, LI values from images were generally greater than the LI values from the quantum sensor. During the reproductive stages, LI values from images were generally lower than those obtained by the quantum sensor, which was partly attributed to the better discrimination of FGCC for senescing vegetation. Using images to measure LI was easier and faster in prostrate canopies, and less sensitive to soil microrelief and changing sky conditions. The quantum sensor was useful for quantifying LI and LAI nondestructively in different canopy layers. Final growing season shoot dry biomass determined by either method was within 5% of the observed biomass.