Deriving a Simple Spectral Reflectance Ratio to Determine Cotton Leaf Water Potential

ABSTRACT

Leaf water potential (LWP) is an important indicator of plant water status and irrigation scheduling based on LWP is superior to other methods. In this study, a simple reflectance ratio was developed to predict LWP of cotton plants. Cotton plants grown outdoors in pots were subjected to three irrigation treatments of well watered (WW), 60% of WW (WS60), and 40% of WW (WS40), starting from squaring stage through ball opening. The LWP, fresh and dry weights, photosynthesis (Pn) and hyperspectral reflectance were measured on 90 leaves from different treatments on two consecutive days at flowering. Similar measure ments were made at weekly intervals on 3 leaves in each treatment throughout the experiment. All possible ratios of reflectance at different wavelengths were calculated after deleting bands with noise and those strongly influenced by atmospheric moisture content. Leaf water content (LWC) was poorly correlated with Pn, in contrast, a strong exponential relationship was observed between LWP and Pn. A simple reflectance ratio, R1689/R1657, had a significant (R2 = 0.68; P < 0.001) linear relationship with LWP. The identified ratio predicted the LWPmeasuredweeklywith high precision (slope = 0.89) and closely followed the 1:1 line. Further validation of this ratio is required under field conditions before sensors can be developed based on this reflectance ratio.

Key Words:

• Cotton
• leaf water potential
• irrigation
• leaf water content
• reflectance ratio