Balancing Soil Minerals (Pt2)

In this second post about Balancing Soil Minerals I want to look at the soil report, and what it means. Any attempt at balancing the minerals in your soil has to start with what is already present and available to plants, and ultimately to you. In the my last post on balancing soil minerals I posted the results of my soil test. Here is that report again.

balancing soil minerals

Balancing Soil MInerals. Soil Test Report

 

Balancing Soil Minerals – Reading the Test Report

As I described in my last post there are two sets of test results here. Both are fairly similar, so I’ll concentrate on the second column of results, the one for my new polytunnel site.

Soil Depth in Inches

The standard depth for analysis is 6 inches, which roughly equates to plough furrow depth. This gives some interesting points of reference. The estimated weight of an acre of soil, 6 inches deep, is 2 million pounds. Therefore when we look at the trace elements at the bottom of the report, which are recorded in parts per million, a level of 1 roughly equates to two pounds of mineral per acre in the top six inches of soil. It makes calculations a bit easier to do later. The pounds per acre figure  also roughly equates to grams on a 100 sq ft bed. 100 Sq ft (i.e 5 x 20 feet, or 4 x 25 feet) is the standard size of a bed used in the Grow Biointensive method promoted by John Jeavons. I don’t know if that’s a coincidence, but laying out a smaller growing area into beds of this size makes calculating how much of a mineral to add much easier.

Total Exchange Capacity

I’ll try to explain this as simply as I can. It isn’t neccessary to understand all of it, but it might help. Minerals are held in the soil in a number of ways including as part of the parent material (rock/clay), in the bodies of living or dead plants and animals, dissolved in the soil solution, and loosely held (adsorbed) onto the surface of clay and humus. Minerals/chemicals normally have a positive and a negative charge. An example of this is table salt, which comprises of a  positively charged bit, Sodium, and a negatively charged bit, Chlorine. When dissolved in the soil water they can separate. Clay particles in the soil can hold onto the positively charged bits (known as Cations). These are loosely held onto the surface of the particle. Many of the major plant nutrients are positively charged Cations (Calcium, Potassium, Magnesium) etc. Plants can take these from the clay, and exchange them with Hydrogen. Humus has the same ability to hold on to cations, but also anions, the negatively charged bits. The main point of all of this is that the ability of any soil to hold onto minerals, and not have them washed out by rain, depends on the amount of clay and humus that it has. The more clay and humus that the soil contains the greater the potential it has for holding minerals.The terminology for this is Cation Exchange Capacity (CEC). So a soil with very little clay would have a low capacity for holding these cations, whereas a heavy clay soil, with a lot of humus would have a high ability to hold them. To give an analogy, if you think of it as the number of car parking spaces available, with the cations as cars. A sandy soil would be like a high street shop. You’d be lucky to find a single space outside of it, so no cars. A pub would have a small car park, an out of town supermarket would  have hundreds of spaces, and then you get to the multi story. This would be the equivalent of a clay soil with lots of humus. Thousands of spaces for cars (minerals) to come and go.

The row titled Total Exchange Capacity is the reported level in my soil. 1 would be a sandy soil with little humus, 10 is the level for a ‘heavy’ soil. My Exchange capacity is over 22. A really large capacity, with masses of potential. If you think of these readings like a plate of food. A soil with a Capacity of one is capable of holding one plate of food (minerals), a heavy soil 10 plates, mine is 22 plates. Not bad.

Soil Ph

The next row is soil ph. This is a measurement of the relative acidity/alkalinity of the soil. 1 is very acid, 14 very alkaline, 7 is neutral. My soil is 6.9, which is good. As different minerals are made unavailable at different levels of acidity, a level of 6.4 may be optimum, but I’m pretty happy. It’s worth noting that soils can be strongly alkaline, but low on Calcium, which is possibly the most important plant mineral. Other Cations like Magnesium and Potassium can raise the alkalinity of the soil. This is another reason why you need a proper soil test report before balncing soil minerals, rather than just a ph test.

Organic Matter Content

This may be a bit controversial for mulch gardeners, but you don’t need massive levels of organic matter in the soil. In my climate, a level of 7% is ideal. To put this into perspective, a six inch depth of soil is 150 mm, so 7% of that is 10.5 mm, or just under half an inch. Even if all of your organic matter were to ‘walk away’ each year, you only need to add half an inch of compost a year to maintain a reasonable level of organic matter. This is why I think that mulch/no dig gardening is so wasteful. In order to suppress weeds gardeners are applying 2 inches or more of compost. No need for this level, and it may lead to excessive levels of Nitrates in your food, and an increase in pests and diseases on your plants.

My organic matter % is 9.2 on this site, so I don’t need to add anything. I probably will as I need to do quite a bit of digging to weed, level the site, and form beds wihin the polytunnel. As the increase in oxygen will lead to more organic being ‘consumed’ by soil microbes, I’ll add some to compensate.

Anions

Anions are the negatively charged bits of soil minerals. The two measured here are both important for plant growth. I’ll go through what the levels mean in my next post.

Exchangeable Cations

Cations are recorded in two places. The first set concentrates on those present in the largest quantities/relevant importance. These are split into Desired Value, Value Found, and Deficit. The value found is the most important part, as there is a range of opinion as to what is the desired level of any mineral. These ranges are not all of the ones that I’ll be working towards. Again, I’ll cover how I’ll work that out in my next post.

Base Saturation Percentage

This line takes the values found in the previous set of readings and puts them into a percentage. This is important as when we are looking to balance soil minerals, we want to create an optimum ratio of minerals, as well as an optimum overall level or quantity. A quick look at this set of readings shows that my soil is low in Magnesium and Sodium. The Magnesium level should probably be raised a bit, but my reading suggests that Magnesium binds the soil more tightly, which wouldn’t be great on my clay.

Trace Elements

The most important trace elements are shown here. As a recap on the measurement stuff that I wrote earlier, if you look at the level for Managnese, it is recorded in parts per million (p.p.m). The level is 18 for this column, so that means that I have 18 ppm, which is the equivalent of 36 pounds of Manganese in the top 6 inches of each acre, or 36 grams per 100 sq foot bed.

The Soil Test Report Final Thoughts

As well as being the way to start balancing soil minerals here, it also provides a baseline figure to evaluate how effective my mineral balancing program is going to be. That’s pretty important as I’m likely to try and include stuff like Actively Aerated Compost Tea in my tailor made solution. Subsequent Soil Test Reports will allow me to compare the before and after readings. One of my criticisms of permaculture is that there is a lot of talk about how deep rooted perennial plants and trees will bring minerals up from the subsoil for use by other plants, but I’ve not seen any ‘proof’ that it works. Soil testing would be one way to show whether it works, or is just another good idea in theory, but not in practise. Hopefully somebody will take up the challenge and create a proper trial.

Look Forward to Soil Mineral Balancing (Pt3)

The final post in this sequence will look at how I calculate what the ‘right’ levels of minerals are for my soil, and what I’m going to do to bring those minerals into balance. I hope that the post wasn’t too hard going, and I’m happy to reply to comments if something needs to be explained better.

Take Care

Deano

 

 

 

 

11 thoughts on “Balancing Soil Minerals (Pt2)

  1. Patrick Whitefield

    Hello Deano,
    This is another really useful post. Thank you.

    There’s only one point I’d question. I’ve never hear this thing about magnesium holding soil together before, but I think what must be meant is that it attracts clay particles to it. It’s bivalent, as is calcium, and that’s an important reason why calcium does this. The effect of it is to gather individual particles together into soil aggregates, leaving pore space in between, ie improve soil structure. If I’m right, the net effect is the opposite to what you assume.

    Cheers, Patrick

    Reply
    1. Deano Martin Post author

      Hi Patrick
      Three of the most recent books that I’ve read say that this occurs, although as one is based another that’s only really two sources. I didn’t notice any references, but am guessing that they are relying on research by Albrecht, Hopkins, or another soil scientist. If I find a link to the source articles, I’ll attach them.
      Hope that all is well
      Deano

      Reply
  2. Darius Namdaran

    I’m wondering about the relationship of minerals in the soil and what the plants take up. Can you take a measure of rock dust put it on the soil and just leave the plants to pick up what they want and leave what they don’t?
    Is it ok to have too much of a particular mineral?
    Also, I was reading how important an anaerobic/ aerobic cycle is to releasing the minerals from the soil. That ‘no dig’ creates pockets of anaerobic conditions which release ethylene which encourages the clay to let go of minerals making them available to the plants. When the clay does it raises oxygen levels and returns the soil back to aerobic.
    Does the report show what minerals are not just present but what is being released to the roots?

    Reply
    1. Deano Martin Post author

      Hi Darius
      I hope to answer some of those questions in the next post, but the last one is relevant here. This test shows available minerals. I am assuming that there may be unavailable minerals that are not reported. As icrobial activity may increase those over time, it suggests to me that an ongoing series of tests, perhaps every two years for me, is called for.
      The ratio of minerals and surplusses will be covered in the next article.
      Where were you reading about the aerobic/anaerobic cycle that you mention? Was it in relation to the ethylene cycle?
      Thanks for the mention of Holmgren in your other comment. Where was the bit about digging/aerating the soil? I’m going to go through it again, but you could save me some time.
      Cheers Mate
      Deano

      Reply
  3. Pingback: Permaculture and the Ethylene Cycle Myth - The Sustainable Smallholding

  4. Douglas Smith

    Look forward to seeing part 3 in due course. Based in Hertford, UK I’m also interested in the remineralisation approach (Steve Solomon) and will be interested how and where you source required minerals the UK. Did you also have / use the Laverstock soil test, or choose to send the soil sample to the states for parity with the recommendations given there? Prior to reading more on Solomon, I had a test from Laverstock (http://bit.ly/wfIQJa) and would be interested seeing if the results here can be used – like your own results, one of the issues it flags is Magnesium and the ratio to Calcium.

    Thanks,
    Douglas

    Reply
    1. Deano Martin Post author

      Hi Douglas
      I’ve delayed writing part 3 as it stated becoming a summary of the stages of the book. I’m going to shorten the draft and concentrate on what my amendments are, rather than an explanation of how I arrived at the prescription.
      I used Logan labs. The Laverstoke test was unreasonably expensive compared to the $20 that they charged. I used rockdust, kelp, Manganese and copper and magnesium sulphate, plus Borax. I have Sulphur to add too, but am waiting for empty beds.
      Cheers
      Deano

      Reply

Leave a Reply

Your email address will not be published. Required fields are marked *