Canopy water deficit detection in paddy rice using a high resolution field spectroradiometer

Abstract

Reflectance factor spectra in the visible, near, and mid-infrared ranges from canopies of rice plantings that were flooded throughout the crop season (controls) were compared with the treatment drained on a predetermined date, and sheltered from rainfall, to induce water stress. Spectra sampled at 5 nm intervals in the 400–900 nm range and 10 nm intervals in the 900–1900 nm range and their first derivatives were statistically analyzed by ANOVA for two sources of variation, cultivars and water stress, each measurement date. Near infrared (1190–1320 nm) and mid-infrared (1600 nm) band reflectances, and the first derivative at 1230 nm responded promptly to the removal of paddy surface water even for complete ground cover (LAI = 5) during vegetative development. The first derivative at 960 nm, corresponding to a small water absorption band, detected the water status of canopies about 10 days after drainage. Response in the first derivative preceded by a few days the leaf water content deficit, the visual symptoms of wilting and leaf roll, and the decrease in visible red (RED) and near infrared (NIR) reflectances expressed as the normalized difference vegetation index, NDVI = (NIR - RED) (NIR + RED) . Findings indicate that high spectral resolution reflectance measurements and their first derivatives in near and mid-infrared ranges offer a promising method for early detection of water stress in rice canopies.