Changes In Cotton Leaf Reflectance and Pigmentation with Water Stress

Authors: Sassenrath, Gretchen; Zimba, Paul; Gramig, Greta

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/3/2007
Publication Date: 7/20/2007
Citation: Sassenrath, G.F., Zimba, P.V., Gramig, G.G. 2007. Changes In Cotton Leaf Reflectance and Pigmentation with Water Stress. National Cotton Council Beltwide Cotton Conference, 9-12 January, 2007. New Orleans, LA.

Interpretive Summary: Detecting water stress in cotton (Gossypium hirsutum) over large production fields for irrigation scheduling is difficult and error-prone. We are exploring methods of detecting the onset of water stress using remote sensing methods that will allow rapid, accurate determination of crop and soil moisture status over large areas to better plan timing of irrigation application. Water stress in plants is known to alter pigments in the leaves. These pigments may offer a method of detecting the onset of water stress in cotton. In this study, we measured changes in photosynthetic and stress pigments in cotton plants exposed to different levels of moisture deficit. We found differences in the pigment contents only in the most severely stressed canopies. This lack of difference in pigment content with water stress may be due to errors in the sampling protocol. However, it may also indicate that changes in stress pigments, and canopy reflectance in the visible portion of the spectra, are limited in their ability to detect the onset of water stress.

Technical Abstract: Timing of irrigation in cotton is critical to maintain optimal yields. Traditional methods of monitoring crop status for scheduling supplemental irrigation are time consuming and error prone. Remote sensing offers the potential for rapid, accurate determination of crop status over wide areas. We assessed physiological and reflectance changes in cotton with water stress, with an end to developing correlations between physiological indicators of water stress and plant reflectance that can be monitored remotely. The results presented here describe differences in leaf and canopy reflectance and photosynthetic pigment content of leaves for two production systems, conventional and conservation tillage, with and without irrigation. Stress responses typically are reflected in altered carotenoid content, particularly of xanthophyll cycle intermediates. Therefore it is expected that content of carotenoid pigments relative to total chlorophyll content will increase with increased water stress. Relationships between pigment content and reflectance data should yield similar patterns.