Measurement of Cotton Leaf Area with the LAI 2000 Canopy Analyzer

S. K. Hicks, R. J. Lascano


Measurement of cotton leaf area index (LAI) by traditional methods is time consuming and labor intensive tasks. The objective of this study was to evaluate the use of an LAI-2000 canopy analyzer to measure the leaf area of cotton. The instrument consists of a "fish eye" lens that projects its hemispheric view onto five detectors arranged in concentric rings. Impinging radiation below 490 nm is measured for five zenith angles from readings made above and below the crop canopy. LAI is then computed by the control module from the attenuation of light from above to below the canopy using a canopy gap model. The sensor and the viewing area cannot be exposed to direct solar radiation when readings are made. Readings should be made at dawn, dusk or during the day if a method of shading the sensor and viewing area is devised. A simple canopy gap test for canopy homogeneity must be made before using the instrument to estimate LAI. If the canopy gap test is not significant then a wide sensor field of view can be used. LAI is then measured by making an above canopy measurement and four below canopy measurements arranged in a transect across the row. If the canopy gap test is significant LAI is measured by reducing the sensor field of view to 45 and by making two sets of transect readings with the sensor field of view aligned with the rows and across the rows. The canopy gap test is more likely to be significant on wide row spacings and when LAI is below 2. The direction of the sun in relation to the sensor in the morning or late afternoon hours can result in either an over or under estimation of LAI. LAI readings made around solar noon were within 10% of the actual LAI measured with a leaf area meter.

Reprinted from Proceedings of the 1994 Beltwide Cotton Conferences pg. 1331
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998