Relationship between spectroradiometric and chlorophyll measurements in green beans

Abstract

Individual linear relationships were established between total chlorophyll and SPAD readings, while a unique linear relationship was determined between chlorophyll a and SPAD readings for three green bean cultivars (Phaseolus vulgaris L.). Greening of young expanding leaves at the top of the canopy of all cultivars was associated with low transmittance and reflectance in the PAR region. However, transmittance and reflectance responses of young leaves were different between cultivars. Leaf senescence was associated with an increase in transmittance in the PAR region, but no changes were obtained in the Near‐InfraRed region (NIR). Top young leaves and middle canopy fully expanded leaves of the three green bean cultivars presented a similar transmittance in the Visible and NIR regions. Although the correlations between reflectance and SPAD values of young expanding leaves and that for the inverse‐log reflectance were relatively weaker than that obtained for transmittance either for the same leaf age or different leaf ages, the results suggest that the SPAD meter may be used to provide a rapid estimate of leaf transmittance and reflectance in the field.