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Soil organic matter(SOM)

Discussion in 'Organics' started by MustangStudFarm, Jan 24, 2018.


    MustangStudFarm Well-Known Member

    Hey guys, I just had my soil tested again and it looked pretty good at first glance but I noticed that Sulfur was high. I read a few articles and it said that high sulfur does not have a direct affect on anything but Ph and it will impede N intake... I continue reading and I find out that Organic Matter % has a direct influence on how much Sulfur is in the soil, the higher the organic matter the more sulfur there will be. I continue reading and find out that the optimum level for organic matter is between 3-10% and anything above ten percent is going to hinder micro nutrient uptake. My Organic Matter is at 57%!!!

    I have spent all night reading and trying to wrap my head around this one and the only thing that I have been adding was peat moss to dilute the potassium and phosphorus abundance in my soil and I think that is where my crazy organic matter numbers came from. I am going to copy and paste a few articles that I came across because I didn't understand how big of a problem this really is...

    Organic Matter (O.M.)
    Increasing organic matter levels will help with the soil texture, structure, drainage, aeration, water holding capacity and availability, nutrient availability, root development and dramatically improve soil biology. Organic matter (humus) holds three times more nutrients than most clay soil types and up to 5 times as much available water.

    2% or less organic matter is considered poor. Over 4% O.M. to 10% is ideal. Above 10% organic matter can often inhibit micro-nutrient uptake, and if composed primarily of woody materials will greatly reduce nitrogen availability. (Microbes breaking down wood cellulose use large amounts of nitrogen.) Most crop soils benefit from adding organic matter every year; especially if tilled or intensively farmed. Adding composts, manures, cover crops, and other organic mulches are the best choices for increasing organic matter.

    Sulfur Toxicity
    For practical purposes, sulfur toxicity should be considered impossible. Excess soil suffer can prevent the uptake of other elements though - nitrogen for example. If your soil contains excessively large amounts of sulfur, increase irrigation and ensure that fertilisers being applied to the soil do not contain sulfur. Two pounds of sulfur can leach out one pound of either calcium or magnesium. Sulfur test levels of 20 ppm are the minimum recommended level and around 30 ppm is ideal.

    MustangStudFarm Well-Known Member


    MustangStudFarm Well-Known Member

    The first time that I tried to "fix" the soil, I just used peat and perlite at a ratio of 1:1:1 of Build a Soil, peat, and perlite. It got the high #'s down to something manageable but that is when the organic matter % jumped. However, the sulfur issue has not arisen yet. Ph was low along with Ca, Mg, and trace minerals.

    MustangStudFarm Well-Known Member

    I tried to fix the Ca, Mg, trace mineral problem with glacial rock dust, basalt, and oyster shell flour. I don't understand where the huge spike in Sulfur and Organic matter came from? It is the test on the left, the one on the right from an outdoor garden.

    Tyleb173rd Well-Known Member

    Could you provide a link that says organic matter should be 4-10%? That seems incredibly low for cannabis farming.
    NaturalFarmer and Wetdog like this.

    Wetdog Well-Known Member


    Before you go down this particular rabbit hole there is a concept that you haven't fully grasped that underlies a LOT of your (and many others), problems, false starts and poor decisions AFA soil. That is:

    Agriculture (soil farming/gardening) and Horticulture (container growing/constructured soil (less), mixes, are related, but do not necessarily translate on a one to one basis.

    What works, or is a problem in agriculture doesn't mean it works, or is a problem in horticulture. This 'soil organic matter' *problem* is a good case in point. About the only thing in my mix that isn't SOM is the perlite and the SOM is easily over 50%, but yet there are no problems with nutrient uptake (Macro or micro).

    Is any of this making any sense? Once you understand that they are two different animals, life does get a bit easier.

    MustangStudFarm Well-Known Member


    ShLUbY Well-Known Member

    i will have to agree with Wet on this one. One must remember that the majority of studies are done surrounding the agriculture industry, because that's where the majority of the money is. Not all things translate from one field to another, say from major Ag studies, to indoor horticulture. Sometimes those studies need to be taken with a grain of salt. As Wet has mentioned... we've been mixing our soils with 30% OM right off the rip of the initial mix, and experiencing fantastic results, so that right there is evidence that shows over 10% OM is fine. I'd be interested to see a side by side with 10% OM vs 30% OM and see if there are any differences. it may be microscopic (differences in soil biology), or it may be expressed in the morphology of the plant.
    Rasta Roy, Tyleb173rd and Wetdog like this.

    MustangStudFarm Well-Known Member

    The only thing that I am worried about is the extreme excess of sulfur in my soil now. If organic matter is a direct reflection of how much sulfur that I have stored in my soil, I have a LOT of sulfur in my fucking soil... Sure, they want to say that Sulfur has no toxicity issues except for low Ph and locking out N. If you ask me, that sounds like toxicity issues. So, if sulfur is not mineralized until the Ph raises. Then everytime that I try to raise the Ph, I will mineralize more sulfur and it will buffer the Ph back down and I will always have N deficiency issues. I don't know how much sulfur is in my soil because it is hiding in 57% organic matter, it sounds like there is a real abundance.

    Organic matter. About 95 percent of the total sulfur content of most soils is contained in the organic matter. As this soil organic matter is broken down or decomposed, the organic sulfur is mineralized into the sulfate form (SO4=-S).


    MustangStudFarm Well-Known Member

    Alright, this article is talking about soil with high calcium and adding sulfur to lower the Ph. If you switch the sulfur and calcium in this scenario then you have my situation...

    The problem soils are the calcareous soils—those that contain lime (calcium carbonate). This is the same lime used to raise the pH of acidic soils. In many soils, calcium carbonate (CaCO3) is a part of the parent material from which the soil was formed. Soil scientists have found that as long as solid lime is present in the soil, it is not possible to decrease the pH. Remember that statement, because it is the key to the decision on whether the use of sulfur will be practical for the lowering of pH. When sulfur is added to a calcareous soil, sulfuric acid is formed and some of the CaCO3 dissolves, but as long as CaCO3 remains in the soil, the pH cannot be permanently lowered. This resistance to change in pH is known as "buffering." It is very difficult to change the pH of a highly buffered soil, whereas the pH of a soil with a lower buffering capacity can be changed more easily. An analogy used by soil scientists to explain this phenomenon is to compare pH testing to pressure testing of tires. Both a bicycle tire and a tractor tire could be measured at 50 pounds of pressure. When air is released for 10 seconds from both tires, the bicycle tire's pressure will drop several pounds, but the tractor tire will remain very close to 50 pounds of pressure. The tractor tire is "buffered" against pressure change, but the bicycle tire is not.

    Rasta Roy likes this.

    MustangStudFarm Well-Known Member

    I am sorry to keep on this, but how in the hell do I get more sulfur when I add only calcium and magnesium??? When I planted in the mix, I had to cut everything down. I was ready to kick a box of puppies and kittens

    MustangStudFarm Well-Known Member


    MustangStudFarm Well-Known Member

    Here is my theory; When you add sulfur to established plants, you can burn the roots with the inital influx of sulfuric acid. When I added the Ca and Mg, it raised the Ph and released the S and I temporarily had too much sulfuric acid on the roots. By the time that I had my soil tested, the Exchangeable Hydrogen went back down to normal levels... Sulfuric acid is one of the six strong acids and has the chemical formula H2SO4. Exchangeable hydrogen is just representing hydrogen with a -3 charge, which is an oxidizing element...

    MustangStudFarm Well-Known Member

    Here are my clones that in the 5.8Ph soil and they seem to be doing OK. I just dont want to jump into bad soil again and I already lost 3-4+ weeks on this... I should have had these transplanted a long time ago!!!
    ShLUbY likes this.

    ShLUbY Well-Known Member

    those are looking nice dude! I guess the only way to acidify your soil would be to cut the whole mix with peat??? I'm wondering how this is gonna play out for me. I had applied some potassium bicarbonate to my plants cause i saw a little mildew a couple weeks ago and wanted to soak everything, and i forgot to cover my soil with something to keep the runoff from getting into it... my two no-tills have a pH of 7.4 now because of the K bicarb.... so i applied some gypsum as a topdress with some compost and other goodies... i'm hoping i don't burn the shit out of my roots. i will let you know how they're doing when i get back this weekend to check on the garden.
    MustangStudFarm likes this.

    MustangStudFarm Well-Known Member

    I realized what is going on with my stuff...I thought that the sulfur was already in my soil. I realized that I must have mixed some soil that I thought that I got rid of. I followed recommendations from the lab and everything was a sulfate. Look at how crazy high the sulfur is on this test. I'll step out now and stop freaking out... I think that I was interpreting the information wrong.

    Anyways, if you look at how much calcium and sulfur that this mix has and the Ph. There is not much you can do with this soil. It has so much sulfur that it will buffer out any calcium or magnesium that you add to it. This soil might be OK for blueberries or something, I just spread it on my lawn

    rikdabrick Well-Known Member

    I can run your numbers for you tomorrow if you want. I don't think that soil is a lost cause, but you need to bring the pH up. Your manganese numbers look high from a glance and at 5.5 pH that could cause some problems possibly.

    I don't worry about sulfur excess personally. I've seen some huge excesses of it in soil and it didn't cause any problems. A shot of amino acids will help if you experience nitrogen deficiency.

    And for the most part the only micronutrients that are going to be hindered in a high OM soil are copper and manganese so I foliar feed those weekly. I also foliar feed zinc because I run my soil at 85% of the cation exchange ratio and plants seem to metabolize zinc quickly with high calcium.

    Also, for the K-3 test at Spectrum you'll get the most accurate results if you sift out the bigger stuff, so I've been told.

    What were you using to amend for the calcium and magnesium?

    The downside to these lightweight mixes is they don't hold pH very well so it fluctuates pretty easily when you add stuff to it, as I think you've probably seen already.

    You can also call Bill at Spectrum and ask what he recommends. He's a cool guy and enjoyable to talk to.
    MustangStudFarm likes this.

    rikdabrick Well-Known Member

    Have you ran some water through this soil? Everything is in excess besides iron. The nitrate and ammonium might be fine too, I don't run figures for those numbers. Nitrogen I would base more on visuals of the plant.

    Anyway, there's more minerals in that soil than there should be so there's probably some free floating minerals in there. I'd give it a REALLY good flush and test it again if you have enough soil to make it worthwhile.

    The numbers I'd be shooting for are:
    Ca 5865
    Mg 414
    K 538
    Na 40
    P 673
    S 337
    B 5.87
    Cu 33.65
    Fe 337
    Mn 168-337
    Zn 67

    So if you went by the same numbers as me you can see you have excesses on everything and fairly severe excesses on Mg, Na, S, B, Mn and Zn. The Boron is a little sketchy, but it's pretty close to being right on for the amount of calcium you have.

    Also, just FYI, for whatever reason Spectrum always reports OM on the low side. It's one of the few numbers I'd trust Logan labs on more.
    MustangStudFarm likes this.

    MustangStudFarm Well-Known Member

    We started using Logan Labs because of this "High Brix" online group said that they are the company that they used and the tests ended up 1/2 the price as Spectrum labs. It was the High Brix group that gave me the idea to use rock dusts instead of the Lab recommendations. I am positive that I have more Ca, Mg, and trace minerals than the tests are showing. It's just going to take it longer to break down... I was about to use some Epsom salt, but that is what brought my attention to the Sulfur count on my test. I am very close to getting the excessive #'s out of my soil tests and I guess that high S is not too bad but my Ph is 6.2 and I am afraid that it will keep dropping. I don't know how much the rock dust is going to buffer against the S?

    Dangers of nitrogen overuse include: zinc deficiency, copper deficiency, burnt out organic humus and microbes, drives out calcium but leaves magnesium (tighter soil) and depletes sulfur. The more nitrogen that is applied in excessive amounts; the higher the replacement level of the other nutrients that were carried away by the leached nitrogen will have to be.

    Nitrogen and sulfur can leach out calcium. Nitrogen never leaches out magnesium, only sulfur does. The best methods to stabilize proper nitrogen levels are to use and incorporate cover crops, composts and manures before, during, and after each crop growing cycle.

    MustangStudFarm Well-Known Member

    I know that the labs don't test for N levels because they can change so quickly. From what I read, they said that N can leach out of your soil by the time the sample reaches the lab... I have some serious yellowing going on and I am done guessing and adding stuff that might/might not help...

    From the above excerpt about N, it drives out calcium but leaves Mg and depletes S... That sounds like exactly what I need!!! I have some feather meal that came in the mail today and I was thinking about mixing it in with more kelp and basalt. I think that my P#'s are where they need to be so I am going to skip the fish meal.

    My #'s are close enough that I probably don't even have to mix anything with it, but I really feel like my plants have been turning yellow way too fast. Honestly, I don't think that rock dust and feather meal are going to affect this grow anyways. My potassium levels are down to 1/2 of what they should be and that is why I am suggesting Kelp, it will give me the micros and 1-0.1-2 for NPK ratio and a slight boost in Ph. I have all of this stuff on hand already. I learned my lesson on over-doing it also! I think that I am going to mix and plant tonight.

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