Abstract
Estimating leaf area index (LAI) of Vitis vinifera using indirect methods involves some critical issues, related to its discontinuous and non-homogeneous canopy. This study evaluates the smart app PocketLAI and hemispherical photography in vineyards against destructive LAI measurements. Data were collected during six surveys in an experimental site characterized by a high level of heterogeneity among plants, allowing us to explore a wide range of LAI values. During the last survey, the possibility to combine remote sensing data and in-situ PocketLAI estimates (smart scouting) was evaluated. Results showed a good agreement between PocketLAI data and direct measurements, especially for LAI ranging from 0.13 to 1.41 (R2 = 0.94, RRMSE = 17.27%), whereas the accuracy decreased when an outlying value (vineyard LAI = 2.84) was included (R2 = 0.77, RRMSE = 43.00%), due to the saturation effect in case of very dense canopies arising from lack of green pruning. The hemispherical photography showed very high values of R2, even in presence of the outlying value (R2 = 0.94), although it showed a marked and quite constant overestimation error (RRMSE = 99.46%), suggesting the need to introduce a correction factor specific for vineyards. During the smart scouting, PocketLAI showed its reliability to monitor the spatial-temporal variability of vine vigor in cordon-trained systems, and showed a potential for a wide range of applications, also in combination with remote sensing.
Highlights
Leaf area index (LAI, total one-sided area of leaf tissue per unit ground surface; [1]) is a quantitative descriptor of canopy density and it is important index for monitoring vine (Vitis vinifera L.) vigor and for providing precious information to support vineyard management.Leaf area density is significantly correlated with radiation interception and light environment in the fruit zone [2], in turn affecting the canopy microclimate and the plant carbon balance, as well as yield and grape composition [3,4]
The LAIv values obtained from destructive measurements during the campaign ranged from 0.13 to 2.84, in agreement with those normally reported in commercial vineyards [16,17,25]
The results of the comparison between LAIv values from PocketLAI, digital hemispherical photography (DHP) and destructive measurements are shown in Table 2 and Figure 2
Summary
Leaf area density is significantly correlated with radiation interception and light environment in the fruit zone [2], in turn affecting the canopy microclimate and the plant carbon balance, as well as yield and grape composition [3,4]. For these reasons, attempts have been made to forecast vine yields using remotely sensed vegetation indices (i.e., normalized difference vegetation index, NDVI) related with plant vigor and LAI [5]. The application of a unique pesticide dose can results in over- or under- plant protection, with the negative economic and environmental impacts
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