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.