Gamble Ranch Field Demonstration

Napa County

Gamble Ranch is operated by Treasury Wine Estates and is located within the Oakville AVA in the middle of Napa Valley. The ranch is approximately 830 acres in size, of which 525 acres are planted to vineyards. The varieties grown on the ranch are Chardonnay, Cabernet Sauvignon, Malbec, Merlot, Petite Sirah, Petite Verdot, and Sauvignon blanc. There are 11 different soil series on the ranch. The soils are, for the most part, alluvium derived from volcanic, metamorphic or sedimentary rock, but there are some soils derived from weathered volcanic rock as well. In addition, there is a great deal of diversity in the landscape with three different riparian corridors and two areas of oak woodland located on the property. Gamble Ranch is certified sustainable by the California Sustainable Winegrowing Alliance and has the Fish Friendly Farming/Napa Green certification through the California Land Stewardship Institute.

Although Treasury farms thousands of acres in California, they strive to implement sustainable farming practices, especially when it comes to managing their soil. A few years ago, Treasury began converting a lot of their acreage to no-till farming and planting permanent no-till cover crops, including perennial bunch grasses. All 525 acres at Gamble Ranch are now farmed under no-till management. Recognizing the importance to alleviate compaction, and as an alternative to full tillage, Treasury has been using a subsoiling tractor implement known as the Mainardi Plow. The Mainardi Plow has patent curved ripper shanks that rip down to 24 inches without inverting (turn over) the top soil. It must be used when the soil moisture is just below field moisture in the topsoil, so that the shanks can easily be driven into the soil without bringing large fractured clods to the surface. The plow is used every 3-5 years to break up tractor tire compaction and promote deep soil aeration around the vine root zone, while also promoting deeper water infiltration during storm events.

Treasury  has observed and documented a positive response to vineyard productivity using the Mainardi Plow in their Santa Barbara Vineyards. They have just begun incorporating it at Gamble Ranch. As part of a regional soil health field demonstration site, The Napa County RCD and Treasury are measuring and monitoring the effects of the plow on soil properties and vineyard productivity.  The field demonstration site has three treatment plots, 1) No-till with compost application, 2) No-till with compost application and Mainardi Plow, 3) Tillage with compost and green manure cover crops. Baseline soil sampling was conducted in March 2018 before any treatments or tillage were conducted. Soil sampling and analysis happened again in 2021.

Questions this trial is addressing:

  • How does compost application method (surface vs. incorporated) affect soil organic matter accumulation, soil health, and vine growth?
  • How does tillage, compost incorporation, and Mainardi plowing impact grape quality and or yield?
  • How does tillage, compost incorporation, and Mainardi plowing impact soil carbon sequestration or soil carbon reduction from each treatment?
  • Does the Mainardi plow effectively reduce tire compaction and does it improve soil properties and vine health/grape yield?

Trial Description:

In two vineyard blocks that vary in soil type, monitor response of soil health to three management treatments:

  1. No-tillage with compost application (15 tons per acre), not incorporated.
  2. No-tillage with compost application (15 tons per acre), and Mainardi Plow sub soiling in tractor tracks.
  3. Tillage with compost (15 tons per acre) and annually seeded plow-down cover crop.

Non-tillage is the typical vineyard floor management at Gamble Ranch, therefore each block will have a control of no-tillage under all other typical vineyard practices.

Block Description:

Cabernet Sauvignon, 8 x 6 ft spacing, vertical trellis. 12 acres

Sauvignon blanc, 8 x 6 ft spacing, vertical trellis. 2 acres

Soil Indicators:

Soils will be sampled following the North Coast Soil Health Hub – Soil Health Assessment Protocol and sent to the Oregon State Analytical lab for analysis.

Vine and Grape Indicators:

Treasury will measure standard vine and grape quality indicators, including:

  • Yields.
  • Grape quality.
  • Leaf water potential using a pressure bomb.

Field Trials and Demos