Estimation of grain quality of rice (Oryza sativa L.) by UAV-acquired vegetation index and climate factors

ABSTRACT We aimed to associate unmanned aerial vehicle – acquired vegetation index (VI) with the percentage of several kinds of imperfect grains and grain protein content (GPC) for use as an indicator of rice grain quality. The cultivars ‘Koshihikari’ and ‘Ishikawa 65’ were grown in the field from 2019 to 2022 at various N application rates. From 20 days before heading to 10 days after heading, the field was imaged with a multispectral camera to construct VI maps. We measured the chlorophyll index at heading (CIG 0) and two climate factors, mean air temperature in the 20-day period after heading (T +20) and cumulative solar radiation in the 20-day period before heading (R −20). At maturity, we harvested plants to determine grain yield and quality. We assessed the percentages of two types of chalky grains basal-white and white-back grains (BBWG), milky-white grains (MWG), as well as other types of immature grains (OTG) and GPC. In Koshihikari, CIG 0 and climate factors were associated with BBWG and MWG, whereas in Ishikawa 65, they were associated with BBWG, MWG, and OTG. Based on these findings, the response of BBWG, MWG, OTG, and GPC to CIG 0 was estimated using the mean T +20 and R −20 values from the last 10 years. We found that as CIG 0 increases, the sum of BBWG and MWG decreases in Koshihikari, whereas the sum of BBWG, OTG, and MWG increases in Ishikawa 65. Thus, CIG 0 is an acceptable indicator of grain quality in rice. GRAPHICAL ABSTRACT