Measurements of leaf area index using optical method (LAI-2000) in oil palm plantation: accuracy and limitation assessment
2006
Wan Ishak | M . A . Awal | J . Endan | M . Haniff
Leaf area index (LAI) is an important parameter for characterizingthe canopy structure of a crop. The LAI, which is often used as a critical variable to simulate different ecosystem models, is difficult to measure directly in oil palm. In this study, optical methods for quantifying variation in LAI under different conditionswere evaluated. It was found that the accuracy of the readings depended on different factors, such as measuring technique, viewcap angle, spatial variability, and height of the measuring point. The measuring technique had an effect on the LAI measurement. Resultsshowed that the Zigzag method underestimated the LAI compared to other methods. The LAI by the Zigzag method was 11.6% less than the LAI by the u one above and four below" technique and 5.7% less thanthe LAI by the""one above and eight below" technique. The LAI obtained by the "one above eight below" technique was 6.2% less thanthe LAI obtained with the "one above four below " technique. Resultsfrom the investigation of the effect of view cap on LAI measurementshowed that the view cap strongly influenced the LAI calculation andLAI decreased with increase in the view cap angle. PCA LAI valueswere also affected by spatial variability and height of the sensor.PCA LAI values increased with increase in sensor height above groundwith a maximum LAI value (2.77) at 2.5-meter height above ground andminimum LAI value (0.932) at 0-meter height from ground. Maximumvalues of LAI were obtained for all directions at 0.5-meter distancefrom the trunk and minimum LAI values were obtained near the tip ofthe frond. The PCA LAI values increased by about 5% - 50% with increase in distance from the frond tip to frond base.
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