Comparison of different protocols for indirect measurement of leaf area index 2 with ceptometers in vertically trained vineyards
نویسندگان
چکیده
18 Background and aims: Most optical devices for indirect measurement of leaf area 19 index (LAI) from canopy-transmitted light are tailored for homogeneous canopies, thus 20 limiting their application to discontinuous canopies such as vertically trained vineyards. 21 This study evaluates the influence of sun position on the reliability of LAI estimates 22 provided by a ceptometer and proposes a measurement protocol for use of such 23 instruments on vineyards under direct illumination. 24 Methods and Results: Ceptometer readings at several sun elevation and azimuth angles 25 were recorded in two fields. Leaf area index estimated at different sun positions using 26 several measurement protocols were then compared against destructive leaf area 27 measurements. The best results when the sun position departs from the zenith (sun 28 elevation < 40°) are achieved by reading the transmitted, photosynthetically active 29 radiation (PAR) in all the inter-row spaces, whereas measurements below the vines are 30 suitable only when the sun illuminates close to the zenith. 31 Conclusions: The homogeneity of the canopy fraction measured along the ceptometer 32 at each individual reading is a major requirement in order to obtain non-biased LAI 33 estimates. Therefore, the protocol followed to measure the transmitted PAR at every sun 34 position proved critical for the accuracy of LAI determination. 35 Significance of Study: This study provides guidelines for reducing LAI uncertainties 36 associated with vineyard canopy structure in LAI estimation with linear-array optical 37 devices such as ceptometers. 38 39
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