Survey of the accuracy and rapidity of several methods for vine leaf area assessment

Abstract

Vine leaf area is an important viticulturel parameter. Because its assessment is difficult, leaf area is not frequently taken into account. In this survey, several techniques of vine leaf area estimation are compared for their accuracy and rapidity. Leaf area is highly correlated with leaf blade fresh or dry weight. This method is destructive, because all the leaves have to be removed, and thus it can only be applied after harvest. Leaf area can also be estimated by the measurement of the lenght of two upper lateral veins. This method is precise, but very time consuming. Sample size reduction to one leaf out of four measured does not affect the quality of the estimation, though sample reduction to one leaf out often does. For accurate assessment, samples must be taken from multiple shoots. The third method utilizes the correlation between leaf area and shoot length. This technique combines precision and rapidity, though a standard curve should be established for each cultivar and stage of vine development The percentage of light extinction through the vegetation can be measured by means of an L.A.I. 2000 device. Values are closely correlated to leaf area index and vine leaf area can be deduced when vine density is known. This method is very rapid (only one to two minutes per vine) but it does not distinguish between the primary and secondary leaf area. Moreover, the L.A.I. 2000 device is very expensive. Digital photographs were taken of the vines studied. Assessment of the percentage of leaf surface area, after binarisation of the image, does not lead to an accurate estimation of vine leaf area. The choice of a technique for vine leaf area estimation among the ones tested, will depend on: a) required precision, b) time availability, c) the need to dispose separately of primary and secondary leaf area, d) the possibility to invest in equipment and e) the possibility to remove leaves.