The harvest method is one of the oldest methods, used for various vegetation types from crops to forests. A sample to be treated destructively has to be collected 4-5 times during the crop life cycle (i.e., sampling is done at 10-15 day intervals from seedling emergence) or relative to some of the developmental stages of the crop (emergence, flowering, physiological maturity). At each collection date, leaves are separated from the other parts and sub-samples are selected for leaf area measurements. Then leaf area models have to be calibrated as: leaf area = (leaf length x leaf breadth) x k, where k is a species specific coefficient depending on leaf shape and indentation (k = 0.5 for triangle, 0.75 for grasses such as sorghum and maize, near 2/3 for many dicots). Leaves of the subsample are dried, weighed, and the dry leaf weight ratio is computed. Finally, LAI is computed as the dry weight of leaves x dry leaf weight ratio.
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