Evangelos D. Gonias, Derrick M. Oosterhuis, Androniki C. Bibi, and Larry Purcell. University of Arkansas, 1366 W. Altheimer Dr., Fayetteville, AR 72704
The most common method of measuring the fraction of radiation intercepted by the crop canopy is using a line-source quantum sensor (Rosenthal and Gerik, 1991; Heitholt, 1994; Sadras and Wilson, 1997; Kiniry et al., 2005). The fraction of intercepted radiation is calculated by measuring photosynthetic active radiation above and below the canopy. In cotton, with a row spacing of 1 m, a 1-m line quantum sensor is placed perpendicularly across the two rows. The limitation of this method is that measurements should be taken in unobstructed sunlight, close to solar noon (Board et al.; 1992, Egli, 1994). Purcell (2000) described a method for estimating light interception in soybeans that was not affected by the above limitations. In this technique, ground area coverage is determined by digital images taken above the canopy. The canopy coverage values were similar throughout the day, and were correlated in a one-to-one relationship with light interception measurements made with a line quantum sensor at solar noon (Purcell, 2000). In this study this method was tested for use in cotton.
