Aug 072011

Most people don’t get them. (Soil tests that is). Gardeners who grow organic have been taught to believe that adding organic material in the form of compost will solve all problems. According to people like Michael Astera and Steve Solomon this is not the case. (There’s a rumor that Michael and Steve are joining up to co-write a book on this subject). You can actually have too much organic material in the soil. However, if necessary minerals are not in the material you use to make compost, compost additions will not add minerals to the soil. Michael Astera gives this explanation:

“Soil is formed from the rocks that break down to make it. In most cases, that means the bedrock beneath your field. For young soils, whatever minerals were in the bedrock are the ones in the topsoil, and in pretty much the same proportion. Sandstone, limestone, granite, or basalt will all form a soil with a different mineral balance, and different types of each one will make different soils.

As soils age over thousands and millions of years, their mineral content changes as minerals are eroded or leached away. River bottom lands are usually the richest soils because they have been formed by all of the rocks and minerals that have leached or eroded from the whole watershed.

Over the past 170 years, some researchers have looked into which soils with which mineral balances grow the most yield, or the most nutritious food (not the same thing). What I work with and recommend is an “ideal” balance of minerals for growing food to feed people and animals. This is pretty much the same mineral balance for any food crop from radishes to pastures to fruit and nut trees.

The only way to know what minerals are in a given soil is to get it tested by a lab, with the right test. The next step is to compare the results against the “ideal”, figure out what’s missing or what is in excess, and then add the missing minerals in such a way that the excess, if any, is dealt with at the same time.

In theory, after you did that, your soil would be as rich and fertile as any soil in the world, and the crops would be as nutritious as any crops ever grown anywhere. From there on, you would just add small amounts of whatever minerals were taken up by the crops or leached away through precipitation and irrigation. For a few years you would need to have the soil tested regularly, but after a while you could probably come up with a good idea of what your particular soil needed on an ongoing basis.”

So what does a soil test look like?

Here’s my most recent test. The “hot garden” is a 400 sq. ft garden I added two seasons ago and has not been amended with minerals. The “old garden” is my original garden plat and has 1360 sq. ft. of planting area. I had a previous soil test and amended the old garden with minerals prescribed by Mr. Astera.

2011 soil tests (link to a pdf file to view)

Each soil test cost $20. Michael Astera’s book explains how to read these and how to compute the minerals necessary. But since my mind does not bend that way I paid his very reasonable consulting fee to get an RX for my garden.

Prescriptions for gardens are given as an amount per 1000 sq. ft.

Here’s what I need to add after harvest this fall:

Amendment        Hot Garden                                  Old  Garden

Calphos              30 lbs X.4 = 12 lbs                           30 lbs x 1.36 = 40.8 lbs

Gypsum              35 lbs x .4 = 14 lbs                           30 lbs x 1.36 = 40.8 lbs

Hi-calcium ag lime          0                                            20 lbs x 1.36 =  27 lbs

Sea Salt                  3 lbs x .4 =    1.2lbs                           3 lbs x 1.36 =    4 lbs

Borax                      4 oz. x .4 =    1.6 oz                           8 oz. x 1.36 = 10.88 oz

Epsom Salt            4 lbs x .4 =    1.6 lbs                          4 lbs x 1.36 =  5.44 lbs

Copper Sulfate       1.5lbs x .4 =     .6 lbs                           0

Zinc sulfate              2 lbs x .4 =      .8 lbs                           2 lbs x 1.36 =  3.5 lbs

Total minerals needed:

Calphos        53 lbs

Gypsum        55 lbs

Ag lime          27 lbs

Sea Salt          5 lbs

Borax             13 oz

Epsom Salt      7 lbs

Copper sulfate .61lbs

Zinc sulfate      3.5lbs

Clearly, this adds a new element to gardening. If you are just growing a couple small beds of lettuce this probably won’t be too important to you. However, if you are seriously working to grow significant amounts of nutritious food, why not try make you plants as nutrient dense as you possibly can?

Understanding the principles of nutrient loss and re-mineralization will also make you a more savvy consumer and give you the basis for asking your local commercial growers some tough questions. Question # 1, do they do soil tests? Question #2, how do their veggies rate on a Brix scale? (More on Brix to come soon).


  10 Responses to “Soil Tests”

  1. Another, not to dense easy to understand, book on soils that is useful is The Soul of Soil: A Soil-Building Guide for Master Gardeners and Farmers by Joe Smillie and Grace Gershuny

  2. You need sea salt? Spray from storms isn’t enough for you? Seems very strange.

  3. Re sea salt: science doesn’t lie, does it?

  4. I’ve got a gazillion rocks in my garden soil, with most being about the size of an acorn. I’ve been waiting for them all to break down into soil, but so far I’m not seeing much progress. Watering them doesn’t seem to do any good.
    Any ideas?

  5. Wait one million years, then Rototill.

  6. Thanks, one lap around our Galaxy should just about do it. Gotta go now.

  7. Hey Mike — I thought the rocks are supposed to GROW not break down. Or reproduce, which is clearly what’s going on over here in my field/raised beds/etc. It’s a garden, not a gravel mine after all

    There are three testing labs in our region which understand our conditions that I can recommend. Use one of these rather than shipping back east or wherever. Be aware that the cost of the analysis is separate from the cost of their recommendations based on the analysis. You must tell them specifically what you will be growing in order to obtain useful recommendations.

    Just across the border in Surrey, B.C.
    NORTHWEST LABS 1 800 889 1433, 604 514 3322, Fax: 604 514 3323
    They service regional (Cascadia) agriculturalists.
    Various tests of the soil profile possible: topsoil as well as subsoil.
    Testing of composts, soil-less mixtures, manure.
    Also can do plant tissue analysis and feed stuffs testing.
    Water testing.

    Their knowledge of our specific agricultural region – the Fraser/Nooksack Valley – is to be highly valued!
    Call U.S. and Canada Customs for current protocol for taking or mailing samples. Accurate Labeling is crucial for border crossings entries of samples. Call the lab for their recommendations as to packaging and labeling and timing between sampling and lab receipt of samples.

    Services similar to Norwest Labs. – No feed testing that I recall.
    They service the agricultural and horticultural industry in our region; they do site visits as part of the
    testing protocol, therefore you get “one on one” contact with their scientists (your consultants). I have used them when overseeing installation of my landscape projects for public projects to verify the contractor is using the soil and fertilizer mixes I specified for the project. Not cheap, but you get what you pay for, right?

    A & L LABORATORIES, Portland, Oregon.
    I have used them to test farm soils. I found them a bit difficult to work with as regards recommendations, probably because they consider small farmers not worth their time. This is the lab IFM uses if you send a sample to them for testing.


  9. Correction:
    The testing lab in Surrey is Norwest Labs rather than Northwest Labs

  10. […] When Michael or Steve Diver analyze your soil test they write a prescription. Back in August I posted the prescription I will use on our garden this […]

 Leave a Reply

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>