Series: The Organic Gardening Collection
In 2006, I started an organic gardening service, one of the few in my city at the time that was truly organic.
This was my first chance to apply – to other people’s gardens instead of just my own – what I had learned from studying the organic approach to gardening. It was mostly successful but I had some problems dealing with weeds in some lawns and the occasional other pests.
It’s not just a matter of applying lots of everything, but small amounts of the right things.
It took me a while to figure out that it was because I was neglecting to do what is outlined in this lesson, and in some future lessons on supplementing nutrients to balance the nutrient ratios in the soil.
Most of my students have skipped this step, too, to the point where I now say, “I know you’re probably going to skip this step the first year, so all I ask is that if things don’t work for you like they should, you’ll go ahead and get your soil tested and then start to apply the appropriate fertilizers to balance the nutrients.”
I understand the hesitancy to go pay $50+ for a soil analysis, and then more money on the fertilizers. I know many people don’t want to do it, and the good news is it’s possible to grow food with just organic matter and homemade recipes, so don’t worry if you don’t want to jump into this right away.
That being said, these lessons are about growing the most nutrient-dense food and plants possible, so it’s definitely necessary to know. To me, this is crucial and it’s what’s missing in most organic gardening resources that often focus more on composting and perhaps applying a few organic fertilizers, often fertilizers that can make things worse.
While talking to local farmers and soil experts can garner some useful information about the most common soil deficiencies and excesses in your neighborhood, this information is often not as useful in an urban setting.
Many of our practices, or those of people who previously gardened our soil, can make the fertility in our back yard much different than our neighbors. The soil may change when compost or topsoil has been brought in, pesticides sprayed, chemical or mineral fertilizers applied. If you or someone else has applied dolomite lime for 10 years in a row, that may have drastically changed the nutrient balance from its original state.
To get better information about the soil, we need to do tests. The qualitative tests from the home soil inspection lesson are part of this.
We also do a couple of quantitative soil tests. We want to do these different tests because if we make decisions based on only one, there is a good chance we’ll make the wrong choices. It is much better to have data from multiple sources in order to make more an informed decision.
While the numbers you get from the soil analysis examples on this page are useful, it’s important to also remember to look at your soil, weeds and plants to see what they’re telling you, and to bring all of this data together. A soil test alone doesn’t always give accurate enough information to make big fertility decisions. Looking at your garden is just as important.
Most home soil test kits that you can buy are pretty much useless.
In fact, even professional soil labs give widely different results from each other based on the methods they use, even though they have good equipment. Still, these are many times better than the average home kit, although a decent home kit is manufactured by LaMotte and sells for $600-$700.
Soil tests measure a moment in time, but the soil changes throughout the year, even over the course of a few days. Temperature, moisture, and biological activity each have an effect.
In the end, the results coming back aren’t even close to 100% accurate. There are too many factors to take into account. In fact, some people argue that professional soil analysis is a waste of time. It’s true that they are rough estimates, but their usefulness has been proven by thousands of soil consultants who have successfully used them to improve soils and crops.
It’s important to always use the same lab because at least it will be using the same methods from year to year if it’s a good lab that has been around for a while. That way you can more accurately compare numbers between tests you do over the years.
Still, you will come across some well-known organic gardening adherents who don’t like soil tests.
In The Organic Method Primer, a wonderful book by the way, Dr. Bargyla Rateaver says they’re basically useless because they’re based on the incorrect idea that plants take up most of their nutrients in ionic form.
The main test I recommend partially overcomes this. Still, while the results we get back aren’t 100% accurate, we know they’re helpful because soil management decisions based on them have been used for decades with great success.
There are also some things we can do to improve accuracy. We can take a good soil sample, choose a good soil lab and get the right tests done.
When to Test
It’s worthwhile to sample your garden soil once a year in order to track long-term changes and continually work to move your soil towards an ideal level.
The goal isn’t necessarily to get all the way to the ideal, but just to move in that direction. I sample once each year on big food gardens — in early spring or fall.
If you just want to do it once in the first year and then forget about it, that’s fine. Just make sure you don’t skip doing it once. I would suggest sampling one more time, a year after the first one, to see what effect your inputs have had and to see where you need to go from there.
You’ll probably see that you’re better off than the previous year, which may cause you to want to sample again the following year. That’s great, but if not, that’s just fine. At least go for one sample.
It’s very important to sample at around the same time each year, under the same environmental conditions.
After harvest is a good time to sample, although some people like to test their soil in spring. Spring or fall is what I say, and the sooner the better.
After a season of growing, soil should be loose and easy to sample, and won’t have been fertilized recently.
You don’t want to sample during a drought or if you’ve applied fertilizers in the last month that supply high doses of specific nutrients. Liquid kelp and fish wouldn’t affect the test much, but mineral and chemical fertilizers would. Take a quick note of when you sample, including the date, temperature and a qualitative indication of the moisture level.
How to Take a Soil Sample for a Lab
Farmers will separately test different parts of their field, but this gets too costly for most home gardeners, so you need only do one test, but you do want to combine at least three samples from different parts of your garden. If you’re primarily interested in growing food, take three or more samples from your vegetable gardens and combine them.
Skip the areas in your yard that have obviously different soil conditions, or test them separately.
Most labs suggest your shovel should go down 6 or so inches to get a soil sample. Market gardeners looking for a complete soil analysis often go down as far as 3-4 feet, being careful to take different samples perhaps every 12 inches in depth, in order to evaluate what’s going on in the various subsoil layers.
Home gardeners will want to get soil from the surface down to at least 6 inches.
The easiest way to do this is to dig a hole first and then you can use your shovel to take a nice vertical slice of soil from the side of that hole that will include all depths.
What I mean is, you don’t want all of the sample to come from 6 inches down, and you don’t want it all to come from near the surface. You want soil right from the surface, excluding coarse mulch but including any soil crust, down to your testing depth.
Taking a sample with a soil core sampler. There are many variations on this type of device, but a clean shovel will usually do just fine.
When you’re taking these samples, be sure to keep everything very clean. The shovel should not be rusty. The pail needs to be sparkling clean and cannot previously have contained fertilizers.
After the samples have been thoroughly combined in a pail, usually 2 cups are placed in a new, clean bag or container to be shipped to the lab. Some labs are happy with 1 cup. Most labs don’t care if the sample is wet or dry.
The results are only as accurate as the sample you send, so be sure to combine samples from several different places in the garden, to the correct depth. Don’t include much organic debris, and keep the whole process uncontaminated. Sample from the exact same spots each year.
Mark them in your journal or with scarecrows, birdhouses or pet rocks on site.
Choosing a Soil Lab
While it may be tempting to drive a sample over to your local soil lab, this may not be the best option.
Right now, most soil labs aren’t doing a great job. They’re still stuck in the same chemical mindset of soil management that many of the colleges are teaching.
While local soil labs do often have valuable knowledge and data on local soils, if they aren’t focused on organic or biological soil management, I don’t use them. We just don’t speak the same language.
Also, many soil labs that are evolving their thinking to more holistic soil management methods are making some of the same old mistakes.
If you find a lab that suggests liming based on pH or total base saturation without considering what nutrients you specifically need, look elsewhere.
If you find a lab that offers organic recommendations as being secondary to chemicals, you may want to look elsewhere. You can figure these things out by reading their website or giving them a call. Some of the ecological soil scientists do advocate small amounts of certain chemicals, but the focus should still be on organic inputs.
It’s hard to make precise recommendations for amounts of manure, as compared to chemicals.
I have two favorite soil labs. There are many others out there (here’s a good list of some of them). For me, I ship to these instead of using my local lab.
(I would even recommend shipping to them if you live in Canada. You just have to fill out a couple of extra forms for customs requirements. That said, A&L Labs in Canada does do a base saturation test, although not from an organic perspective).
If we’re going to go through the trouble of doing a soil analysis, let’s do it right so we can feel confident about the results. These labs are doing the kind of tests that I believe are most useful, based on the research of Albrecht, Reams, Callahan and Andersen, to name just a few. Current prices are $50-$75. You can use another soil lab, just make sure they do CEC/base saturation testing and/or weaker acid Reams/LaMotte style testing or a similar test:
- Based in Grand Rapids, Michigan and led by Dr. Phil Wheeler and Ron Ward, authors of The Non-Toxic Farming Handbook.
- Not only are they doing base saturation and Lamotte testing, but they work with biodynamic farmers and other energetic systems such as electronic scanning that we will look at in a future lesson. I highly recommend them.
- You can get both the base saturation and Lamotte tests plus recommendations, see their website for details.
- Based in Fairmont, Minnesota and led by Dan Skow, co-author of Mainline Farming for Century 21.
- These guys do great work, too. They rely on Reams testing for their recommendations, but they will do a base saturation test for you, too, see their website for details.
Important: If the rest of this lesson seems like gibberish, don’t worry – if you choose a good lab, they will do all of this for you and you can just follow their recommendations…
Michael Astera sent me an email after reading this article, which I published with his permission, and then Dane Terrill from Crop Services International (CSI) emailed a response to that, which I will publish as soon as I have his permission:
Michael. “Both Crop Services International and Int’l Ag Labs use the Morgan test. At pH 4.8, it only measures what is readily available to the crop, not any reserves or potentially available minerals. It is of no use for estimating CEC or measuring cation saturation %. Jon Frank has openly admitted that. The only accurate modern tests for CEC are the Mehlich 3 and the ammonium acetate tests. Ammonium acetate only measures exchangeable cations and is not accurate for other elements. The M3 has only been around since 1984, ten years after Albrecht died. My understanding is that Albrecht used the Barium test to measure CEC, which results in toxic waste and has been discontinued. Adolph Mehlich developed the Barium test for CEC originally in the 1930s, then spent the rest of his career trying to develop an accurate test for CEC plus most other elements that didn’t result in hazardous waste. First the Mehlich 1, then Mehlich 2, and finally Mehlich 3, which was published the same year he died in 1984.”
Phil. “Isn’t CSI still doing the CEC test?”
Michael. “A few years back I remember their head lab guy writing an opinion piece in which he slammed the Mehlich 3 test and said he didn’t believe in it and wasn’t going to use it. 🙂 If they or Int’l Ag Labs is offering an Albrecht test they may be using the M3, but I would ask.
Another interesting tidbit is that I’ve read that the various A&L labs (A&L Western, Great Lakes, East, Canada) are all separate private companies. It used to all be one company but they split up at some point while keeping the A&L name. I mention this because different offices may be using different testing methods for their standard soil test. I have written quite a few soil Rx’s from A&L Western lab reports with no reported problems.
Dairyone.com aka agro-one.com seems to be a good lab and only charges ~$15 per sample, but their CEC calculating method isn’t to be trusted; I always re-calculate their numbers using the Brookside method (p 153 in Ideal Soil 2.0). One lab I do not trust and would not recommend is Spectrum Analytic. Sloppy work and cutting corners, and their CEC numbers are definitely not to be trusted. Over the past eighteen years, Logan Labs has proven the most consistent and reliable for me.”
Dane from CSI. “We use Logan Labs for our Soil and Tissue testing, NOVACropControl (Netherlands) for SAP Analysis, Earthfort for our Quantitative Biological Testing and as Certified Soil Foodweb Advisor perform Qualitative Biological Testing in house on soils, composts and compost teas. As you (or Michael) may or may not be aware, Logan Labs does in fact use the Mehlich III and Ammonium Acetate extraction for CEC/Base Saturation. IN ADDITION to the CEC testing, they also performed the LaMotte testing extraction for CSI (Dr Phil encouraged them to do this testing for us years ago). Effective Dec 2016, they, Logan Labs, have discontinued this testing for us and are using the Saturated Paste test for in-season monitoring IN ADDITION to the CEC. To our knowledge, no article was written slamming the CEC test nor saying he didn’t believe it. Perhaps the head lab guy was inferring that for growing a crop, the Saturated Paste gave a better picture of availability than CEC. That being said perception of the reader is reality…and that I cannot argue!”
For anyone who wants help with soil testing and wants to learn more about it, I encourage you to check out Michael’s website and book, The Ideal Soil, and for lab testing, I continue to recommend Crop Services International.
Cation Exchange Capacity
A soil test will include a value for CEC. The more clay and organic matter, the higher this number will be.
Here are some recommended numbers, although they will vary depending on who you ask. Sandy soils low in organic matter will have a CEC between 1-10. They have very little ability to hold onto cations. The 20-25 range is getting to be decent, but 25-40 is ideal and would probably mean you have good organic matter and a decent amount of clay.
This clay loam doesn’t look too appealing without organic matter, but it’s a good starting point for mineral soil in terms of CEC.
Above 40 is high clay and/or organic soil that may include a lot of material such as peat. Pure organic soils, such as a peat bog, go as high as 100 CEC.
The CEC value on a soil test isn’t always particularly accurate. A better indicator of CEC may even be the simple ribbon test. Take half a cup or so of your soil, make sure it’s moist, and squeeze it into a ball.
Form it into a ribbon. If you can’t do that, your CEC is low (sandy soil).
If you can form it into a long ribbon, your CEC is high (clay). A simple test, but potentially more effective.
A lower CEC soil that has a lot of sand needs to be fertilized and probably watered more often because it can’t hold onto either for very long. On the up side, it’s easier to balance the nutrient ratios since a smaller amount of fertilizers added can make a big difference to the small amount of nutrients already there.
A higher CEC soil that has a lot of clay and/or organic matter doesn’t need much fertilizer or water, but if the nutrient ratios are out of balance, it can take a lot of fertilizer to correct them.
The first main test we probably want to get done is called a base saturation test, sometimes referred to as a CEC test.
It gives us an indication of the percentage of base cations, or positively charged ions — calcium, magnesium, potassium and sodium, possibly aluminum and importantly, hydrogen — in our soil.
The significance of the base saturation test is that it includes hydrogen, which makes things easier for us.
Hydrogen isn’t a plant nutrient, but the amount of hydrogen ions present has a big influence on the soil’s nutrient profile.
If you can’t get a base saturation test, another test is called an exchangeable cation test and it doesn’t include hydrogen. This makes it more time-consuming and difficult to interpret properly.
Much of the initial research that produced the numbers that follow comes from decades of work started in the 1920s by Dr. William A. Albrecht at the University of Missouri.
He actually started working there as a microbiologist and I believe he was initially studying inoculation of legumes with various Rhizobia bacteria. He came to the conclusion that the nutrients in the soil were having an impact on the quality and yield of the food crops, so he started researching the impact of nutrients and nutrient ratios on the crops.
He perfected the use of the base saturation test. A total base saturation of 75% means the CEC sites in our soil are occupied 75% by the bases and 25% by hydrogen.
But more important to us are the specific numbers, and here’s the magic formula. The ideal results are 60-75% calcium, 7-15% magnesium, 2-5% potassium, 0.5-3% sodium, and 10-15% hydrogen, and a few percentage points for all of the other micronutrient cations, such as iron and copper.
We don’t know precisely why nature has settled on these numbers. What we know is that often, the closer the soil gets to these numbers, the healthier the soil and plants become.
When I say we, I don’t mean everyone. Some people disagree with this method, claiming there is not enough research proving its effectiveness. Their main argument is that all soils are different and there is no one formula that fits them all.
Soil naturally comes in many different types, and it could be argued that plants evolve to be adapted to the soil type of their native ecosystem.
This is certainly true. We could use more research. What is also true is that this method has worked for thousands and thousands of people over at least the last 60 years.
It has worked for me as well because I’ve used the above labs, which are doing it right, using Albrecht’s system or something similar.
Neal Kinsey, co-author with Charles Walters of Hands-On Agronomy, is also doing it right. He helped bring Albrecht’s system to us. There are other labs doing a base saturation test without using Albrecht’s system, and making fertilizer decisions based on those results may not be as effective.
The only research I’ve seen that disproved the effectiveness of using the base saturation test for fertility management was poorly conducted, not even using Albrecht’s system, among other issues. Albrecht’s system does work in the hands of a good lab.
Back to the numbers. Again, these ideal percentages vary depending on who you ask and on testing procedures the lab is using. On sandy soil, calcium goes down closer to 60%, magnesium up to 10-20% and potassium potentially up to 6-8%.
This is because the magnesium and potassium help the sandy soil to bind together. It may be that the numbers are different for some trees and ornamental plants, but I’ve never seen this data anywhere, so I’ve always applied them to all plants.
They certainly work for various kinds of foods all over the world, from corn to bananas to other fruit trees to coffee.
Grasses seem to prefer base saturation percentages closer to those that are ideal for sandy soils.
It’s very important to note that the amount of each nutrient in your soil is not as important as having the correct percentages. In fact, a lack of nutrients is not the problem in our soils. The nutrients are there.
The problems are that they are out of balance and the soil food web is not healthy and diverse enough to extract what is there.
If you were to take a soil sample from a healthy forest, a soil lab would probably tell you that soil was very low in nutrients. What the forest has is a highly functional soil food web to keep the nutrients recycling in the system.
It certainly doesn’t have anyone adding fertilizers.
Getting the soil food web working in our own soil is one of the most important goals on which we need to focus.
And we don’t need to add much in the way of fertilizers, but correcting the nutrient ratios is important to create an environment in which microbes
Ideal Soil Nutrients
- 60-75% calcium (60% for grasses and sandy soils)
- 7-15% magnesium (10-20% for grasses and sandy soils)
- 2-5% potassium
- 0.5-3% sodium
- 10-15% hydrogen
One reason you want to find a good lab and stick with it is that they will have their own precise set of ideal numbers based on the procedures they use. Neal Kinsey works with Albrecht’s exact system, and he wants the numbers to be very close to 68% calcium and 12% magnesium.
He says he won’t give you recommendations based on another lab’s test because he doesn’t know the intricacies of their procedures.
They may have found that 75% is the ideal calcium percentage based on their methods, and that’s just fine. He finds if you get below 10% or above 12% magnesium on his test, you’ll probably run into some issues.
Magnesium is the central atom in the chlorophyll molecule, so plants can’t photosynthesize well if it’s deficient, like this Feijoa tree leaf.
It may seem somewhat arbitrary to focus on only these few nutrients.
While it’s true that there are many other nutrients needed mostly in smaller amounts, Albrecht arrived at the conclusion that these main ones are the most important to get right, especially in the beginning of a soil management program.
Overall, Albrecht’s work has been ignored by conventional agriculture but championed by ecological farmers and gardeners. You won’t learn about it in most gardening and farming courses, but buy some books from Acres U.S.A. or go to their annual conference and you will learn more about these topics.
One other criticism of this test is that in order to extract the minerals from the soil sample, labs use some fairly strong acids. They argue that these acids release nutrients that aren’t really available to plants because they are so tightly held by the soil that plants can’t extract them.
This is partially true for many labs, but Albrecht didn’t use the very strong acids that many labs use. They were certainly stronger than the acids used in the Reams test I’m going to show you next, but Albrecht was very concerned with finding the plant-available nutrients, too.
The analogy often given is that strong acids tell you what you have in your long-term soil savings account. Weaker acids tell you what’s in your soil checking account, so which nutrients are more readily available to your plants. Using water instead of acids tells you what you have in your pocket, so which nutrients are available today, but not necessarily tomorrow.
The strong acids pull too many nutrients and the water-soluble tests don’t pull enough. The weak acids are the most useful, and while I agree this Albrecht test is not perfect, I’ve seen how it’s useful to compare year after year results and look at the trends.
This test helps us determine what mineral fertilizers we will apply to build the base foundation of the soil in the long term.
It’s important to still look at what weeds you have growing to see if they are telling you what the soil test is telling you. You may have 75% calcium from your test, but your garden is full of grassy weeds that indicate a calcium deficiency.
If buttercups and docks are out-competing your lawn, you may have a nutrient imbalance..
That’s one reason why we do more than just the Albrecht test. The more sources of information we have, the better.
Along with the base saturation test, you may have some anions tested, such as phosphorus and the nitrate form of nitrogen. Organic matter isn’t generally tested for minerals on a soil test.
The nitrogen test, therefore, is not especially reliable because about 98% of soil nitrogen is tied up in the organic matter.
There are other factors that make it difficult to get an accurate result. Some labs ask you to bring in a sample at just a couple of degrees above freezing to improve the results, but it’s just not feasible for most of us.
That being said, labs do give you a number for nitrogen. In theory, nitrate nitrogen levels that are too high may contribute to increased blossom drop, decreased fruit set, and increased frost damage and winter kill.
If the cation form of nitrogen — ammonia nitrogen — is low, which is very common, it indicates a lacking soil food web.
That needs to be addressed in order to bring the level of this form of nitrogen up, which is necessary for optimal fruiting and flowering. More important to us is how much organic matter we have in the soil and whether we have the microbes to convert some of it into usable nitrogen.
Phosphorus is another tricky one.
There are a few different tests used to determine how much phosphorus is in the soil, but it’s difficult to get an accurate picture. The interpretation of a phosphorus test is again very challenging because phosphorus uptake by plants is many times higher from organic matter than from mineral soil. There is a better nitrogen and phosphorus test coming up in the next section.
The Lamotte/Reams Test
This is the second test I do.
The Albrecht test is good, but if we want the full picture, we don’t stop there. Carey Reams was one of the most influential scientists for ecological agriculture, an outside-the-box thinker.
He developed a testing system to give you an indication of what your plants might actually get from the soil, even more so than the Albrecht test. The Reams test lets you know more about which nutrients are biologically active in your soil.
To be clear, we’ve been looking at two different testing procedures — the test championed by William A. Albrecht uses stronger extractants to measure CEC, cations and anions, while the Reams test uses weaker extractants to measure nutrients. I ignore the anions such as nitrate and phosphate from the base saturation test but rely on them more from the Reams test.
The Reams test uses the Morgan procedure and the relatively weak acids from the LaMotte testing kit.
These acids are more like those produced by plant roots, therefore the test reveals more about what the plant can actually get from the soil, regardless of how much of each nutrient is in the soil.
Plants release carbonic acid into the soil, as a byproduct of their own metabolism, which then helps extract nutrients from the soil.
You could be sitting on a bed of limestone that might show up as having a lot of calcium in a base saturation soil test, but a Reams test may indicate it’s not available to plants.
Some labs use different testing solutions than the LaMotte kit, but as long as they are following guidelines similar to those of Reams, it works for me.
Incidentally, it won’t say Reams test on the paper, but if you look for these numbers I have below all lumped together, you’ve found it.
After many years of observation, analysis and the help of colleagues and students, Reams settled on the following as being the amounts to strive for in pounds per acre using his test.
Reams-Based Ideal Nutrient Levels in Soil
Calcium 2,000-4,000 lb./acre
Magnesium 14% of calcium
Phosphate 400 lb./acre
Potash 200 lb./acre
Sulfate 200 lb./acre
Nitrate nitrogen 40 lb./acre
Ammonium nitrogen 40 lb./acre
Sodium 20-70 ppm
Again, these numbers are for food, but I use them for all soils.
There’s no need to memorize them, as you have them right here. When you get a Reams soil test back from a lab, you can compare your results to these numbers (and they probably have even done that for you).
They may use slightly different numbers depending on their methods and on your plants. They also may give the numbers in ppm instead of pounds per acre, where 1 ppm equals 2 pounds per acre, so ideal phosphate would be listed as 200 instead of 400, for example. From there, the lab will tell you which fertilizers to add to the soil in what amounts.
They may give it to you in tons per acre. One ton per acre equals about 45 pounds per thousand square feet.
With this test, you’re aiming for a 10:1 calcium to magnesium ratio, or 7:1 for grasses/grains and for very sandy soil.
The lower the ratio gets below 7:1, the more potential for compaction and drainage issues, as well as poor microbial life and unhealthy plants. If you see grass weeds such as crabgrass, it’s probably because it’s come along to help make calcium available.
Crabgrass: a calcium helper?
You’re aiming for a 2:1 phosphate to potash ratio, or 4:1 on sandy soils. If they give you the numbers as phosphorus and potassium instead of phosphate and potash, it’s a 1:1 ratio you want, or 2:1 on sandy soils.
The calcium to magnesium and phosphate to potash ratio are the most important to balance, so worry about them first.
You’re also aiming for a 1:1 potash to sulfate ratio. You may also get a few micronutrients tested. I don’t worry about correcting them until I’ve corrected the main ratios, because I’ve found some of the micronutrients will fall in line when the main ratios are good.
A summary of the ideal ratios follows. Like the base saturation test, the specific amount of each nutrient in the soil is often not as important as their relationship to each other.
Ideal Reams Nutrient Ratios
10:1 calcium to magnesium (7:1 for grasses and sandy soil)
2:1 phosphate to potash (4:1 for grasses and sandy soil)
1:1 potash to sulfate
Organic matter, ORP, pH and ERGS
You’ll probably get a number for organic matter on your soil test.
The environmentally friendly way of determining this is to bake the soil and measure the weight loss because the carbon burns off. Labs are moving to that over the old method, which used toxic chromium.
Still, some labs measure humus, while some measure total carbon, and some labs just guess based on the color, so it’s difficult to know what the number means. Mostly, I use this number to see the trend — whether or not it’s going up with my management practices.
For most people, your soil organic matter will be low, perhaps even down in the 1-2% range. If you’ve been working on your soil for a while, it can be around 5% or even higher.
I prefer just looking at my soil color, and looking and seeing how well it’s aggregating and holding moisture and so on. It just takes a bit of experience looking at the soil to be able to judge the amount of organic matter present.
Oxidation reduction potential (ORP) is a number that has been traditionally used more for determining compost stability, but it’s also being used for soil. It basically measures the state of soil oxidation. The ideal range is 25-30. Too low and the soil is lacking oxygen, it’s anaerobic.
Too high and the soil has so much oxygen that organic matter may be burning up too fast. Like pH, I don’t use ORP for soil management decisions, but you may see it on a soil test.
While pH is important, we’ve already seen how knowing the number isn’t particularly useful to us other than to monitor changes over time. ERGS, energy released per gram of soil, is another number often shown in tests that is covered another time.
Some soils, especially in urban environments, are contaminated with radionuclides, chlorinated solvents, petroleum hydrocarbons, PCBs, PAHs, and heavy metals such as lead, mercury, cadmium and chromium.
Many of these come from human activities such as waste disposal, “inert” ingredients in chemical fertilizers, and industrial mining, agricultural and recreational pollution. To determine if your soil is contaminated, find a local lab that does this kind of testing.
If you have soil contamination, then comes the task of remediation.
Many of the chemical and physical methods of reclaiming polluted soil require a lot of energy and often leave the soil lifeless and unproductive. S
- ome methods go so far as to remove the soil and treat it as hazardous waste.
- Most food growers should do a soil analysis once a year, but if you don’t want to do that, just one time at the beginning is much better than not at all.
- Be sure to take a good, clean sample and send it to a good lab that is doing Reams-style testing and giving organic recommendations.
- While you may get numbers for pH, anions and organic matter, the most important numbers are the base saturation test and the Reams test.
- From the base saturation test, focus on the percentages of calcium, magnesium, potassium and sodium.
- From the Reams test, focus on the availability of nutrients, both cations and anions, as well as the ratios between them.
Another approach is to work with nature by using microorganisms (bioremediation) and plants (phytoremediation) to help with the process. Though it takes longer, these actually improve the soil, while chemical and physical processes can be very destructive.
Fungi are especially adept at breaking down hydrocarbons such as those found in oil. Even the oyster mushrooms I’ve grown in my home are good at this. The book Mycelium Running by Paul Stamets is an excellent introduction to using fungi in your garden and for soil remediation.
Certain plants can pick up nearly all of the heavy metals from a soil. Research, for example, suggests that Brassica juncea (Indian mustard), can take up lead, cadmium and nickel from the soil into its above-ground parts. It can then be harvested and disposed of elsewhere.
Other common plants such as corn, alfalfa and sunflower can be used for this same purpose because of how fast they grow a lot of biomass.
Admittedly, this process just moves the problem elsewhere, but that’s the way it is with minerals. They can’t be broken down like organic molecules. Some argue that lead cannot be effectively taken up by plants, but that fungi may be able to do a good job of removing it.
The specifics of remediation are beyond the scope of these lessons because I’ve never knowingly dealt with a contaminated soil, but I believe testing for and fixing contamination is very important.