Submitted to: American Journal of Enology and Viticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 12, 2007
Publication Date: September 1, 2007
Citation: Blom, P.E., Tarara, J.M. 2007. Rapid, non-destructive estimation of leaf area on field-grown Vitis labruscana grapevines. American Journal of Enology and Viticulture. 58:393-397. Interpretive Summary: Agricultural scientists and agricultural Extension personnel often must measure the amount of green leaf tissue on grapevines or other large perennial crops. This information is necessary for models of crop growth, determination of irrigation effectiveness, application of fertilizers, assessment of plant physiological processes, and recommendations on vineyard or orchard management. It would be easy to measure leaf area on a grapevine by removing all of its leaves and passing them through a device specifically designed to measure the surface area of flat objects. However, removing all of a vine's leaves damages the vine for the current year and has negative lasting effects in subsequent years. Therefore, methods must be devised to estimate leaf area on grapevines and other large perennial crops that minimize the destruction of plant tissue. This is done by measuring some other characteristic of the vine then using statistical techniques to correlate that characteristic to leaf area. Of three easily measured characteristics that were evaluated, the length of a grapevine shoot was best correlated with the leaf area of that shoot. A simple linear relationship between shoot length and leaf area was fairly accurate except during the early part of the growing season. To accommodate the period of rapid shoot growth, more complex nonlinear models are required for the best accuracy.
Technical Abstract: Three potential variables, shoot basal diameter, leaf count per shoot and shoot length, were examined as potential rapid, non-destructive methods for estimating leaf area per shoot, a frequent component of estimates of leaf area per vine. The metrics were recorded in large field-grown vines over five years. Shoot basal diameter, the most rapid method, was not a good predictor of leaf area per shoot. After transformation, shoot length and leaf count per shoot had relatively tight linear relationships with the square root of leaf area per shoot (R2 = 0.90 and R2 = 0.85, respectively). Some of the variation in the relationships that is due to between-year and within-season variability can be reduced by expressing the relationships as a function of thermal time. Furthermore, non-linear models can be fit to the ratio of leaf area per shoot to the rapidly-obtained metrics. Utilizing this ratio approach accounts for the dynamics of canopy development, achieves a single predictive relationship, and increases the accuracy of leaf area estimates during early-season, rapid shoot growth. Early in the season the length and count measurements can be made at an approximate rate of 0.5 min per shoot, but as the canopy develops and shoots intertwine, the sampling rate progressively slows to approximately 2.5 min per shoot.