Overapplied Sulfur for blueberries

subiej(4)April 30, 2012

Hi there-

I'm hoping for some advice. I have been amending a patch of soil over the past year, in anticipation of planting 28 bare-root blueberry plants, which are set to arrive next week. I just got my final soil test back, and realized that, in the fall, I think I tilled in way too much granular sulfur! I had 50 lbs tilled into a 1000sf area, which comes to something like 2240 lb/acre. I have no idea what I was thinking, but this is quite a bit more than recommended.

The soil test shows that, over the winter, the sulfur brought the pH down from 5.7 to 5.3, so it's already pretty close to ideal. However the test also shows that the sulfur level in the soils is *still* quite high (143ppm), so i'm afraid that quite a bit of acidification will take place once the soil warms up. (I'm in Vermont, so probably not much of it broke down over the winter). My organic matter came in at 6%, which I think will help buffer things, but i'm still worried about the abundance of sulfur still in the soil.

I'm considering adding Dolomitic Lime to counteract sulfur's effect, but have no idea: in theory, would this even work? I need to add a little Mg as well, so thought this might help. Please let me know if anyone has any experience with a sulfur overdose.

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Blueberries like 4.5 to 5.5 pH, so you still might be fine. If you have clay soil, the sulfur is much less effective so you'd have needed to add more than recommended, anyway. I'm sorry I can't help more, but I think you might be ok.

    Bookmark   April 30, 2012 at 3:27PM
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fruitnut Z7 4500ft SW TX

First of all the sulfur measured in a soil test is not elemental sulfur waiting to be oxidized, and in that process, lower the pH further. What's measured in a soil test is the SO4 ion, sulfur that's already been oxidized. This is the form used by plants so that's what a soil test measures. A higher soil test indicates that more of the sulfur has already done it's job of lowering pH. The soil test doesn't tell you anything about how much elemental sulfur remains from what you added.

Limestone would raise the pH but your pH isn't too low yet. If you start adding lime you risk yoyoing back and forth from too high to too low. Just let things play out this year and test again in about a year after all the sulfur has been oxidized. Then you can make a sound decision.

    Bookmark   April 30, 2012 at 4:03PM
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Ahhhh, thank you!! That is extremely helpful, fruitnut. Obviously, that changes things quite a bit. I guess that, like fruitmaven said, it might just be ok. I feel so much better...

If I can't add dolomitic lime, though, do you know of a way to add magnesium *without* adding more sulfur, which I believe both sul-po-mag and epsom salts would do? Mg is at 46ppm, which the soil test is saying is only a little low, but I don't want to miss this last opportunity to work amendments into the soil before planting. Thanks again!

    Bookmark   April 30, 2012 at 6:55PM
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blazeaglory(10 SZ22/24 OC Ca)

Try planting a few blueberry plants now and see how well they do. If they flourish then you know. And if they look like crap, then you know:-)

    Bookmark   April 30, 2012 at 7:42PM
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fruitnut Z7 4500ft SW TX


The sulfur in either of those compounds is already oxidized to SO4, sulfate. That form doesn't affect pH so those materials are safe to add in your situation. The soil bacteria oxidize S to SO4. That process is the one that lowers pH.

    Bookmark   April 30, 2012 at 7:47PM
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Thank you- that is amazing. I spoke to the vegetable and fruit advisor at the local agricultural extension at length about this, and she shared my concerns about the overapplication of sulfur, and did not seem to be aware of the distinction between the S in elemental sulfur and SO4 that you're saying is measured in the soil tests and is present in sul-po-mag. Thank you so much for clearing that up for me- very helpful.

    Bookmark   April 30, 2012 at 9:05PM
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