Lessons Learned With Sulfur Fertilizer

One of the best farming books I've read so far.

In this earlier post, I described how we fertilized our pastures with Elemental Ag Sulfur (90% S) last fall at the rate of 50 pounds per acre. Since then I’ve been reading Gary Zimmer’s new book, Advancing Biological Farming (HIGHLY recommended), and I wish I would have fertilized a little differently.

First off, I applied Ag Sulfur because we had too much magnesium on the soil’s exchange sites (over 20%), and we needed sulfur. Sulfur has the ability to attach to magnesium and make magnesium sulfate which either gets taken up by plants or gets leached down and out of the root zone with rainfall. Either way, it gets knocked off the exchange site and frees up room for other elements to attach to the sites. This brings the soil into better, healthier balance for soil life and plants.

In Zimmer’s book, I learned that applying Calcium would have been a better bet. The right calcium fertilizer for our pH would have competed with magnesium for exchange sites in the soil. Calcium and magnesium are like bitter rivals. Always in competition, more calcium will force magnesium to give up exchange sites, and more magnesium kicks out calcium. The reason why applying calcium would’ve been better than Elemental Sulfur is because it takes a healthy soil life (microbes) to work on Elemental Sulfur and convert it into sulfate form so it can get to work on magnesium. Our soil is still coming back to life, and I’m not sure if we have the microbe population that would quickly convert pure sulfur into a usable sulfate form. So, I wish I would’ve used a sulfate fertilizer – calcium sulfate (gypsum), ammonium sulfate, copper sulfate, zinc sulfate, etc. The sulfate would have been usable from the get-go compared to Elemental Sulfur.   Sure, there’s more sulfur in 50 pounds of Elemental Sulfur compared to gypsum, but we need sulfur now, and how long will it take the soil life to break down the Elemental Sulfur?

Also, I learned that Elemental Sulfur is a little harsh on soil life compared to sulfate fertilizers. I’m glad I was conservative and applied it at such a low rate. Zimmer said in his book that he adds sulfur every single year (via a sulfate fertilizer) because sulfur doesn’t stay in the soil. It makes sense – sulfur is an anion (negatively charged element), and it doesn’t attach to exchange sites because they are negatively charged too. Sulfur leaches out of the root zone easily, so it needs to be added regularly.

We want more sulfur because it’s integral in helping plants make protein, which is essential for great pasture quality and good animal health.  We want our sulfur levels to be at least 20 parts per million (ppm), and right now we have around 12 ppm.  We have a lot of missing sulfur, but at least we now know the best way to add it.


8 responses to this post.

  1. Posted by Ian on October 28, 2011 at 4:06 pm

    Great blog. I recently read Gary Zimmers new book also and commend it to anyone serious about improving their soils.
    I am still learning but if I understood what Gary was saying then Elemental Sulphur is best used once the Ca%+Mg% of CEC > 80% and Ca% is > 60% (structure good enough to allow leaching).
    If your Mg% is 20-25% and Ca% is 60-65% (like most of my client’s soils in Australia) then we both will get better value from Elemental S.
    I have only just realised this in the past weeks and intend to ‘ground-truth’ it ASAP.
    Keep up the great blog. Thanks, Ian


    • Thanks Ian! I will keep your theory in mind. I noticed something recently in our fields that I believe relates to sulfur. Our west field was low in potassium, so we spread some potassium sulfate this spring. I broadcasted white clover seed 2 years ago, and it never germinated until this summer. I’m wondering if this has to do with sulfur – i read clover loves sulfur and assumed that was why we couldn’t get clover to etablish (b/c our sulfur levels are always low). Spreading elemental sulfur didn’t have this effect, and the clover didn’t germinate in our other fields where we didn’t spread potassium sulfate. I’m wondering if in our biologically inactive soil, the sulphate was much easier for the soil to take up than elemental sulfur. Who knows! Thanks for commenting!


  2. Hello Kelly,

    Just Ordered Zimmers book today, based on your recommendation.
    I too am quite interested in whether to use sulfur or gypsum on my soil.

    I am looking at your Logan soil test of 11/12/2010.
    Mine is quite similar to yours. I have a base saturation of 66% Ca and 22% Mg.
    Having just finished “Hands On Agronomy” I’d like to get the Mg % down a bit, to like 17%.
    My pH is about the same as your W. field, like 6.7.
    My CEC is about 8.

    What I got from Kinsey is that I can add Ca to displace Mg.
    Or, Sulfur will drive out Mg if Ca is >63%.
    2# of sulfur will drive out 2# of Mg

    Also, when you displace 5% Mg, you gain 5% Ca.

    Since I don’t want my Ca % to go up any more than it has to, I’m thinking adding S is better in this circumstance than adding gypsum. I think all this applies to your W. field.

    I’m probably not understanding all the complexities of this.





    • Hi Erica,

      Great question! I personally would go with sulfur, but if you really want to be sure, you might want to ask Neal Kinsey directly. We met him at the Acres conference, he’s super nice and smart! He has a consulting company. Not sure how much he charges.

      I say sulfur because of the chance of sampling error. 66% Calcium is pretty good, and if the soil test is showing your calcium lower than what it actually is, adding more calcium could throw it over. What are your sulfur levels?

      I just got my Fall 2011 results back from Logan Labs. In Spring 2011, we broadcast 100 lbs/acre of carbonized lime, 250 lbs/a potassium sulfate, and 200 lbs/a compost loaded with micronutrients (boron, zinc sulfate, etc.). I’m hoping there’s lots of “sampling error” going on because, except for the micro levels, the results aren’t good! In the West field, Calcium went lower, to 64%, Mg rose to 22%, and Potassium went way higher to 6.5%. Now the field’s pH is 7.1. Obviously I added too much Potassium sulfate, but I remember thinking that the sulfur would help drive out some of the Mg. Didn’t happen, and the sulfur levels are still below 15. The Mg might be climbing because of the one ton/acre of dolomite lime I spread in 2009 (not thinking). We’re really running up against the problem of very sandy soil – it takes so little fertilizer to change the numbers.

      So to me, sulfur is a safer bet, especially if your sulfur levels are low.


  3. Hello Kelly,

    Thanks for the reply. I think we have a lot to discuss, so as time permits I’d like to exchange soil test reports. Are you interested? If so, how do I send it to you? Are you on the soilandhealth listserve? I just took a soil sample today to send in tomorrow.

    Both of us have low CEC soils, so applying minerals during the growing season is going to be a big part of our culture. Are you set up to apply minerals through your irrigation?

    My situation, in terms of scale, is a bit different from yours, as I have only about 2500 sq ft in the vegetable garden. Another 1000 is coming under cultivation this year. Total is 1 acre.

    I’ve been using Michael Astera’s method for calculating amendments. How have you been calculating yours? We have made a spreadsheet using his methods which I will run for your values, if you like.

    Maybe your pH is bouncing because you have very little buffering (low organic matter, low CEC). Kinsey says it takes 3 years for the full results of a liming to show up. Also, he says sulfur added less than 6 mo ago will screw up the soil test.

    He charges $50 for the test and recommendations. I’m thinking I will send him the same soil as Logan and see what I get back. I am very interested in learning more about this.

    One thing Kinsey say in his book is that chemistry is one foundation for biology. I think this is quite true. If I get the nutrients balanced in the soil, with 25% air qnd 25% water, I’m going to have a whole lot easier time fostering the life in the soil.



    • Hi Erica, yes let’s do that! I’ll email you. Agree with everything you said. I started reading Kinsey’s book again to refresh my brain on this stuff. Also, the time of year I sampled our soil (December) might not be the best. But, we’ve had a very mild fall.
      We don’t use irrigation. We’re very lucky to be in a high precip area – about 4 inches of rain every month here, knock on wood. That’s of course not so great for sandy soil, leaching nutrients like calcium, sulfur, nitrogen. But the rainfall makes for a very nice climate here.
      I bet Kinsey will look at your Logan test and give you his opinion. Kinsey and Logan Labs are both from the Albrecht “true CEC and base saturation” school, so he’s probably familiar with Logan tests.
      I started out using Astera’s methods in my veggie garden and really screwed things up! I played the numbers too hard, trying to achieve the 7:1 Ca to Mg ratio and the 1:1 P to K ratio. My veggie garden is severely unbalanced. I think I chose a site where a stable burned down – tons of nails, etc, so micronutrients and potassium are very high. And my trying to fix it made it worse. I’m aiming for a beautiful garden and very high brix produce, so I’m using Int’l Ag Labs for our veggie garden and orchard. Their testing and recommendations are very weird, but they give me precise steps to take to keep plants producing well while the soil takes its time to get in shape. I still love Astera’s Ideal Soil handbook but have recognized my lack of experience with poor soil, so I’ve sought the help of others.
      For our pastures, I’m sticking with Logan Labs. I learned at the Acres USA conference to get both a standard soil test and a saturated paste test from them. I’m about to do a post on that, but the saturated paste shows the availability of nutrients in a water solution (immediately available for plants). That gave me a lot of insight into what’s going on in our pastures.
      I’ll be in touch – thanks!


  4. Posted by Gale Carr on June 13, 2012 at 12:36 pm

    Does he say anything about tying up the bicarbonates? We have embarked on a project that will put sufurous acid in the irrigation water to lower ph and release tied up nutrients.


    • Hi Gale, no, Gary Zimmer didn’t talk about bicarbonates. I just checked in the index to make sure. I didn’t even know about soil bicarbonates until we got a paste test along with a standard test last December. Ours are too high also, and Joel Simmons from Earthworks http://soilfirst.com/ told us gypsum would help start breaking up the bicarbonates. We met him at the Acres 2011 conference.


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