Barreca Vineyards

Barreca Vineyards

From Vine to Wine since 1986

Soil Testing

Our vineyard went from a backyard hobby to a major enterprise in 2004 when I had some logging done to make a sunnier space for more grape plants. I had some soil testing done soon after that but didn’t worry about fertility.  After almost 20 years of dithering about getting some baseline numbers and setting goals for better outcomes, I entered the fray again this summer with soil testing and leaf testing from a company in Oregon, Apical Crop Science.  Times have changed!

Back then I probably used a post hole digger and a couple of cans and sent dirt to a retiring soil guy in Wenatchee.  This new lab suggests 4 leaf samples per year timed to fruit development and a particular kind of soil sample for sandy soil like mine plus others for other types of soil.  That can cost a lot of money.  I am in a position to pay for what I can learn.  You may not be so lucky.

There is a lot to learn even without submitting samples.  The Apical website showed a picture of a soil probe designed to get soil samples easily at depths of up to 1 foot and then again from 1 foot to 2.  It looked so much easier than a post hole digger!  At just an inch or so wide, it was a tube to push into the ground with a crossbar handle at the top to push and twist with and an opening to get the sample out. Goodbye post hole digger.  Online soil probes cost around $100.  I was in a hurry to get samples, so I made my own.

Homemade soil probe and soil sample jars.

I can already see that mine won’t last forever, so a real one is on the shopping list.  Still, I learned a lot from the get-go.  The picture online shows a probe with the open side plum full of dirt.  Mine went in about 4 inches and plugged solid.  This is not a big deal.  You can just pry that out into a bucket and get another deeper sample.  After a few tries, I had the surface to 1 foot sample and then put the next deeper set in another bucket.  I used two different buckets, one for shallow and one for deep samples and moved around the vineyard.

I could see right away that none of my irrigation water was getting much further than the first 4 inches.  If I had been testing all during the growing season, I would have known that.  So, I ran a sprinkler line all night and another soil sample showed that water had soaked in.  Big lesson right off the bat!

Another thing you can do without any cost is to put your first soil samples in a jar with some water and shake it up.  When the dust (so to speak) settles, you will have a stratified look at the percentages of rocks, sand, clay, and organic matter in your soil.  The rocks and sand will fall to the bottom quickly followed by light sand, and clay with organic matter on top.  Even percentages are fairly ideal.  A lot of rocks would be a problem.  My ground is all fine sand, not ideal but usable with a lot of water and added nutrients. Organic matter is the key to fertility.  It holds moisture, supports fungi and bacteria which in turn transport minerals from sand and rocks to plants.  Too much water is an issue of course.  You want your soil to be moist but drain and to ultimately support earth worms.  Earth is not Dune.  There are no sandworms.  Earthworms don’t like sand, so fertility is an uphill battle in my sandy soil.

Another key indicator of soil health that you can measure at home is PH.  You want it near the middle reading of 7.  Some plants like blueberries and rhododendrons can handle low PH (acid soil).  Others like broccoli and kale prefer more base soil.  PH indicates cation exchange capacity (CEC). (A cation is a positively charged particle.) With near neutral PH more nutrients are available to the plant.    We are getting into complex chemistry here.  I am going to leave that out of this article and hope to come back to it later.

Apical offers soil tests but specializes in leaf extract or “sap analysis” testing.  This is a new field.  Apical uses high-end equipment, similar to what the Environmental Protection Agency uses, and they measure mineral amounts in parts per billion.  You can do a crude imitation at home by squeezing a bunch of leaves enough to get liquid coming out of them.  You can measure the density of the liquid with a refractometer to get a brix reading. (Refractometers cost around $60.)  Low readings around 6º are not good but high readings up to even 22 º are very good health.  These readings measure sugar in the sap and as unlikely as it sounds, bugs don’t like high sugar readings and stay away from healthy plants.

Some of the readings on the detailed Leaf Extract Analysis report can change in a growing plant in different weather conditions and at different stages of growth.  That is why four tests are recommended per year.  It is a moving target.  Close observation of your crops is still the best indicator of what you need to nourish them.   Tests can only show what the factors are at any one time.

I wanted simple answers, firm numbers, definite target amounts and a clear picture of what is going on in my plants and soil from these tests.  I got a lot of numbers, differences between shallow and deep soil and between old and new leaves, all illustrated with colorful graphs and charts.  In correspondence with the Apical lab and Craig Madsen, a local soil scientist, I am learning what this all means.  Definite answers, though maybe not simple ones, will come eventually. One analytical tool that keeps coming up is Mulder’s Chart. The Mulder’s chart represents the interaction between 11 of the essential plant elements. Some interactions boost mineral uptake and others interfere with it.  So far, soil testing is a very humbling experience.  I will be looking at these numbers and Mulder’s Chart this winter.  I encourage you to take some steps in this direction too.  It is best to start testing in the Spring. We need to improve the soil as if our lives depended on it, because they do.

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