Proximal Sensing and Stratified Sampling in Vineyards Provide Direction in Coalescing Vineyard Variability
Runze Yu, Kaan Kurtural,* Luca Brillante, Johann
Terrence Bates, Brent Sams, and Luis Sanchez
*University of California Davis, 595 Hilgard Lane, Davis, CA 95616
Variability in vineyards leads to suboptimal management and is a limiting factor in productivity. A commercial Cabernet Sauvignon vineyard was proximally sensed with electromagnetic induction for soil properties and active canopy sensors to derive a normalized difference vegetation index (NDVI) at modified E-L scale stage 11. The resulting sensing layers were subjected to geostatistical analysis and clustered to derive two management zones. Equal sample size stratified-random samples were allocated within each management zone to ground-truth the management zones. Exposed leaf area per meter of row was 20% greater in Zone 1 than in Zone 2. A completely randomized experiment was established within each zone, with untreated controls where grapevines in Zone 1 received leaf removal on the morning side and Zone 2 received 1.2× the applied water amount starting at the 3 to 5 mm berry growth stage. Grapevine primary metabolism was assessed every 10 days and proximal sensing of canopy reflectance was conducted monthly. Net carbon assimilation and transpiration were greater in Zone 2 until exposed leaf area coalesced at verasion, after which Zone 1 and Zone 2 performed similarly in primary metabolism. Berry skin flavonoids were characterized with C18 reversed-phase HPLC and proanthocyanidin subunits were analyzed by phloroglucinolysis followed by reversed-phase HPLC. There was no difference in yield per vine between Zone 1 and Zone 2. However, berry weight of Zone 2 was 11% greater than Zone 1 at harvest. Total skin anthocyanins or mean degree of pro-anthocyanidin polymerization of the two zones did not differ significantly when treatment application was directed by proximal sensing. The leaf area to fruit ratio of Zone 1 and Zone 2 also coalesced at the end of the season. The results provide proof-of-concept for expanding cultural practices directed by proximal sensing to management zones to decrease vineyard variability in large-scale vineyards.
Funding Support: USDA-SCRI