Spatial heterogeneity of physiological conditions in creeping bentgrass putting greens as assessed by drone‐based remote sensing and in situ measurement of soil water content

A professional diagnosis of the physiological status based on careful spatial observation is essential to maintain the healthy and sustainable conditions and desired quality of turfgrass areas. The objectives of this study were to demonstrate the capability of drone‐based physiological remote sensing and to analyze the spatial heterogeneity of putting greens using drone‐based maps. Multispectral and thermal imagery were acquired concurrently with in situ measurements of soil water content ( θ ) in an experimental turfgrass field and putting greens at a commercial golf course in Ibaraki, Japan, during 2020–2022. High‐resolution maps of the two physiological indicators, that is, canopy chlorophyll index (CCI) as a proxy for chlorophyll content and plant stress index (PSI) as an indicator of transpiration depression, were generated from the multispectral and thermal imagery, respectively. The CCI was closely regressed to the ground‐based dark green color index (DGCI) ( r 2 = 0.80, p < 0.01), suggesting that the CCI could be an alternative to the DGCI. The PSI (0–1) had a close relationship with θ expressed by an exponential equation ( r 2 = 0.92, p < 0.01), suggesting an intrinsic response pattern of transpiration depression to soil water deficit in creeping bentgrass ( Agrostis stolonifera L.) turfgrass areas. A strong correlation was found between PSI and θ ( r = −0.85, p < 0.01) in putting greens. The spatial pattern of θ was so consistent in both the horizontal and vertical axes ( r = 0.8–0.9, p < 0.01) that the site‐specific variability would be persistent. The physiological maps before and after an adverse weather event suggested that these maps will be useful in identifying the vulnerable areas. The drone‐based physiological maps and their synergistic use with in situ θ would provide useful information for turfgrass diagnostics. Further experimental studies are needed to extend the applicability of the methods to different species and environmental conditions.