Spectral response of sweet corn, squash, and beans to nitrogen, zinc and water treatments

The study consisted of six experiments conducted to examine the spectral response of different varieties of corn (Zea mays), squash (Cucurbita pepo) and bean (Phaseolus vulgaris) under variable zinc (Zn), nitrogen (N) and water treatments. Five of these experiments were conducted in the greenhouse during 1988 and 1989. The sixth experiment was conducted in the field during the summer of 1989. Ground-based, remotely sensed data were collected over plant canopies during the growing period, using an Exotech Model 100 AX hand-held radiometer. The Exotech offers filter sets which match the thematic mapper (TM) bands 1 through 4 (0.45-0.52, 0.52-0.60, 0.63-0.69, and 0.76-0.90 μm). Canopy spectral reflectance and derived vegetation indices showed their ability to significantly discriminate among varieties and variable treatments. Soil adjusted vegetation index (SAVI) mimics the normalized difference vegetation index (NDVI) and transformation normalized difference vegetation index (TNDVI) and exhibited all the characteristics of the NDVI curve when there were no soil influences (a single soil type). Red and near infrared (NIR) reflectance factors exhibited ability in monitoring crop growth and development. The TNDVI showed its superiority in detecting variations and in correlating with ground truth data (biomass cover percent). However, the study showed that remotely sensed data were sensitive to variations (varieties and treatments), but the data did not differentiate between them, unless supported with ground truth data