By Dawn Dolan
If you’ve never seen a NDVI (Normalized Difference Vegetation Index) map, they look pretty much like a topography map, which shows a green color in areas denoting healthy vegetation and yellow to red colors in more difficult areas. For the science-oriented, according to the GISgeography website, NDVI quantifies vegetation by measuring the difference between near-infrared (vegetation that strongly reflects) and red light (vegetation that absorbs). Healthy vegetation (chlorophyll) reflects more near-infrared (NIR) and green light compared to other wavelengths. But it absorbs more red and blue light, which is why our eyes see vegetation as the color green.
Perusing old and new NDVI maps of some of their trademark vineyards, Rombauer winemaker Richie Allen shows how he looks for differences within a vineyard. He makes decisions each year to try to influence outcomes and to improve a vineyard or section of a vineyard over time. “I am looking for the best balance for that vine, for that vineyard,” explains Allen. “NDVI helps define our farming and winemaking practices.”
Using NDVI since 2004, Rombauer has changed practices throughout the years based on the insights the newest features that the more modern NDVI maps can bring, but they also use past maps as a record of decisions made to see, over time, if those decisions have been effective or not. According to Allen, all 600-ish acres have some form of NDVI done on them. From 2004-2008, basic knowledge was gleaned about the vineyards from the lower-level mapping done then.
Since 2008, however, issues such as watering, cover crop planting, and calling the harvest are all influenced by the NDVI maps, as well as other technology, like weather stations, field reports, neutron probes for water, petiole testing, and sap-flow meters and pressure chambers. The amount of data can be overwhelming, and it “is hard to synthesize,” says Allen. He wishes for an integrated system that could collate all the information, but for now slogs through masses of data and makes the decisions needed.
Final NDVI maps are gathered about a month before harvest. This information, along with designated sample points set up throughout the vineyard, comes in to the winemaker. Tracking the accumulation of extractable color is paramount for success, states Allen. Knowing pH, TA, and Brix is necessary, but to Allen, the whole extended package is important. He explains that each grape has a maximum sugar load, with the color loading shutting down soon after the grape reaches its maximum sugar load, and “it’s different for each block, varietal, section.”
Once it has gone beyond its maximum sugar load, the grape only reaches higher brix by evaporation, not by accumulation. So harvest is nerve-wracking. “The moment you decide to pick is the moment you give up for that season. That’s the most quality you’ll have in that wine,” says Allen.
Rombauer is leading the way, taking NDVI use to new heights. Heather Rehnberg, Director of Marketing, touts that not only does NDVI influence watering practices, but to state it another way, it also influences when they do not water. With a double dripper system, watering is highly targeted in many of their vineyards, based on what is being seen by the NDVI maps, and supported by observations on the ground.
Rombauer believes they are at the forefront of water economizing and sustainability practices in Napa Valley, and Rehnberg notes that, “Rombauer educates their national sales staff on these practices, so they can pass it on to their distribution points.” They also make sure tasting room staff has a basic knowledge of the mapping and its uses to share with visitors with a higher level of curiosity about farming practices.