A Second Chance with Sulfur

In the previous post, I talked about how magnesium was way too high in our fields.  It’s over 20% of the soil’s exchange sites in our fields, and it should be around 12% to 15%.  I’m kicking myself now for having lime spread this summer.  Very few people spread lime for you around here, but we found one person who would come out.  The only lime he offered was dolomitic (high magnesium) lime.  I really wanted calcitic (high calcium) lime because I knew we had a little too much Mg already from an earlier soil test.  I told him to go for it anyway, and he spread 1 ton per acre. 

Now I have to correct that mistake, but at least there’s a way to correct it – sulfur!  Sulfur has the capability to sink into the soil and take excess minerals with it, essentially knocking minerals off the exchange sites so the soil can get into better balance.  We’re hoping it will kick out the excess magnesium. 

In the nice-to-soil-life-fertilizer world, there are many options for applying sulfur. There’s 90% Ag Sulfur, and there’s some of the sulfate fertilizers, most of which are micronutrients, such as copper sulfate, zinc sulfate, etc.  Our soil is very low in both sulfur and micronutrients, so we could apply either fertilizer. 

We chose to go with Ag Sulfur instead of the micronutrients for a few reasons.  I read in Neal Kinsey’s Hands-On Agronomy that if your macronutrients (calcium, magnesium, potassium, sodium) are out of balance (which ours are), it might cause your soil tests to show lower levels of micronutrients than what you actually have.  This is one reason why we should correct the macros first, then add micros.  Also, macro fertilizers are much cheaper than micros.  So there’s the potential for saving money by being patient.  Another reason for not applying micro nutrient fertilizers now is the chance that our micro nutrients are still tied up by glyphosate (Roundup) in our fields.  Retired professor Don Huber of Purdue University has warned of this effect.  Our fields had several plantings of Roundup-ready soybeans, so they definitely got their fair share of glyphosate.  Of course there are plenty of people saying Don Huber is plain wrong, but since our soil test indicates our micro nutrients are so low, and it would cost thousands of dollars to bring them back up, it makes sense to wait and see if we have more that what’s showing up on a soil test. 

50 lb/a Ag Sulfur went into the spreader.

So back to Ag Sulfur.  Sulfur is a micronutrient, measured in parts per million (ppm) in the soil.  Even though it’s needed in tiny quantities, it’s crucial for soil life and plants.  Neal Kinsey’s book says plants love sulfur, so I’m anxious to see if the grass grows any better next year.  Our levels of sulfur are 10 ppm, and they should be 40 ppm at least.  The levels need to come up at least 30 ppm, which equates to 60 lbs per acre (1:2 ratio).  We went a little conservative and applied 50 lb/acre 90% Ag Sulfur pellets to our fields.  Since we’ll likely have to add a lot of micronutrients, and they’re all in sulfate form, we’ll end up adding a lot of sulfur to our fields.   

We’ll test our soils again in the summer to see if the sulfur levels have come up and if the sulfur was successful in knocking out the excess magnesium.

Update April 2011:  We’ve since learned a better way to fertilize with sulfur.  Read about it here.

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