By Levi Glenn
It's been a little over a year since our purchase of our new parcel. The property is just to our south: 150 acres of rolling oak woodland, a walnut orchard (now removed), and a fair amount of the creek from which we take our name. There are probably only sixty plantable acres and the rest will be left in its natural state. And while there's nothing visible above-ground yet, we're making progress toward planting this beautiful piece of land. The first stage was to find out what we have below-ground, and what we found confirmed our belief that this is indeed going to be a great piece of vineyard.
We knew there were rocks. Lots of rocks, but more importantly white rocks. Limestone rocks. Just how many of these rocks? How does one find out? Invite 13 aspiring soil scientists come to your soon-to-be vineyard and dig a bunch of holes with a backhoe. Using this process, these students turned holes in the ground into this beautiful multicolored soils map:
The main tool a soil scientist has is a soil pit. They dug 41 different soil pits -- typically straightforward holes in the ground 5-6 ft. deep -- across the new property. Grapevine roots can reach down 30 ft., but a 5-6 foot pit gets you the majority of the root mass. Then you assess the layers (technical term: horizons) in the soil. To give you a sense of how we use this data, let's look at one soil pit in the Calodo series. A photo is below, followed by its soil analysis.
The team identified three distinct horizons in the pit: Ap (the top 20 centimeters), Bk (the next 26 centimeters) and Crk (the next 44 centimeters). Below the Crk horizon the team found bedrock. Each horizon is identified by composition, color, texture, plasticity, and pH. Here are the details:
Ap— 0 to 20 cm (0 to 8 in.); gray (10YR 5/1) gravelly clay loam, very dark grayish brown (10YR 3/2) moist; moderate medium granular structure; moderately hard, firm, sticky and plastic; common very fine and fine roots; violently effervescent, many nodules (20.02% CaCO3); slightly alkaline (pH 7.44); clear wavy boundary.
Bk— 20 to 46 cm (8 to 18 in.); gray (10YR 5/1) very gravelly clay, very dark grayish brown (10YR 3/2) moist; moderate medium granular structure; slightly hard, very friable, sticky and plastic; common very fine and fine roots; violently effervescent, many nodules(32.77% CaCO3); slightly alkaline (pH 7.62); clear wavy boundary.
Crk— 46 to 90 cm (18 to 35 in.); fractured limestone (59.48% CaCO3); moderately alkaline (pH 8.07).
If you're wondering about the term "violently effervescent", it refers to how a soil scientist tests for calcium carbonate, or CaCO3. When testing a soil for CaCO3 levels, you pour Hydrochloric Acid on the rocks and if they start to bubble, their calcium carbonate content is sufficiently high to qualify as limestone.Summarizing the information above, you can see the increasing clay and CaCO3 concentration as you go down away from the surface, until you ultimately hit the bedrock. This continuum traces the transition from the surface -- where you're likeliest to find organic matter -- to bedrock, which is nearly 100% limestone. Even better, most of the rock fragments are small pieces of calcareous shale that are easily broken apart by grapevine roots.
For us, the highlight of the above technical information is one number: the 59.48% CaCO3 in the Crk horizon. I have never seen another soil with this high a CaCO3 percentage. CaCO3 is the chemical composition for limestone, the white rock that is so well suited for wine grapes. [Read the Why limestone matters for wine grape growing post from 2010 if you'd like a refresher on its importance.] The Calodo soil series has the highest concentrations of CaCO3, and the Linne soil series also has high concentrations, but tends to be deeper with more clay. These two soils make up the main ridge on our new vineyard property, the teal and yellow colors on the soil map at the top of the page.
There are a total of 8 different soil types that the research team found. They vary widely, from rocky limestone to deep alluvial clays. This will allow us to match each soil type to different varieties. Grenache, for example, is capable of surviving in extreme drought conditions, which help to tame its often excessive vigor, so it's suited to rocky limestone-strewn hilltops like ours, pictured below.
Roussanne on the other hand needs a little more nutrition and would prefer a little more moisture, so it will likely be suited to some of the flat lowlands (think the green lower-lying areas toward the outside of the propery) that have a more clay and better water retention. Ultimately this gives us more information to make better choices when it comes time to plant.
This ridge is first place we are going to plant on the new property. Grenache and Mourvedre are the most likely candidates. We typically assume that the tops of our hills produce the best grapes because of the low yields that the difficult, rocky soils enforce, but hilltops also have the advantage that they won’t freeze. Anywhere there is a slope, cold air drains downward, to be replaced by warmer air from above. Last year I recorded a 10 degree temperature difference from the top of this hill to the bottom. Planting should start in 2014 if all goes to plan. We will start with 5-10 acres and plant a little bit more each subsequent year.
The crew is eager to get started planting, but the day-to-day farming of this property will present its own challenges. We have already ripped the soil to break up compaction, but in doing so we brought an immense number of large rocks to the surface. Those had to be removed before we seeded the hill with cover crop. We know we'll continue to battle the rocks since any time we cultivate it brings more of them to the surface. But the sheer steepness of the property will be the hardest thing to deal with. With slopes from 25-45% on over half of the hill, it will take our most seasoned tractor drivers to tackle this terrain. You can see below the topographical map. The closer the contour lines are, the steeper the slope:
We were fortunate to have not just one soil expert but 14 of them to help us navigate the complexities of our new property. Thank you to Dr. Rice, all your students, and Cal Poly for putting so much time and effort into this project.
Soil Scientists: Samuel Bachelder, Gregory Beaudreau, Eric Boyd, Michael Founds, Laurie Fraser, Aaron Keyser, Jeanette McCracken, Stephen Nolan, Scott Pensky, Natalie Rossington, JaquelineTilligkeit
Soil Scientist and Lead Editor: Emilie Schneider
Project Leader: Thomas J. Rice, Ph.D., C.P.S.S.