REFOLIATION OF ERYTHROXYLUM COCA VAR. COCA. : I. MEASUREMENT TECHNIQUES

Simulation models to estimate annual leaf yields of the coca (Erythroxylum coca var. coca) crop should be capable of describing seasonal fluctuations in yields. Knowledge of how the plant recovers from defoliation at each harvest is essential for model development. Coca plants were grown in a greenhouse and allowed to refoliate. The LICOR Plant Canopy Analyzer, the Decagon Sunfleck Ceptometer, the CID Digital Plant Canopy Imager, and counting the number of leaves initiated on a growing point were used to track progress in refoliation Refoliation occurred in two flushes, both of which could be described as a logistic function of time. Plants began to refoliate in 10d. By 17d after defoliation, canopy cover was ≥50%. The second flush of leaf growth occurred at 40d after defoliation and ended within about 10d. The CID digitial plant canopy imager and the LICOR plant canopy analyzer gave very different estimates of the extinction coefficient for light interception measured at five zenith angles. Extinction coefficient values from the CID digitial plant canopy imager were least affected by zenith angle. The number of leaves per growing point was highly correlated with leaf area index. When canopy analyzer instruments are unavailable or conditions are unfavorable for their use, the simple method of counting the number of leaves initiated on a growing point can give good information about coca refoliation