Our soil tests indicate very low sulfur (9-12ppm), high pH (7.5 - 7.9), and slightly low calcium. Any recommendations for the best products to use to help correct these? We grow annual vegetables in this soil and are certified organic. Thanks!
You could spread some elemental sulfur (which I think is the only form allowed under organic certification) on a yearly basis which would help both with your low sulfur issue AND with lowering your pH. However since sulfur is pretty mobile in the soil, and correct me if I’m wrong, I’d be careful not to apply too much and instead apply smaller doses more frequently. Although, since your pH is high you’ll have to assume that some of the sulfur used to acidify the soil will then become unavailable to the plants… An agronomist would definitely be able to answer that more clearly and give you an appropriate application rate.
A better way to get what you need though would be to spread some cattle manure which is typically high in sulfur, will help even out your pH, and all the while adding to your SOM.
As for calcium I also had a shortfall and I simply used certified organic pelleted poultry manure (which contains 7% calcium) as a spot fertilizer for plants I know need more calcium than others (Solanaceae especially) and it worked quite well for me.
It is difficult to address one particular problem- you need a complete soil test( perhaps you have) which includes your trace elements and base saturation. It is best to get your base saturation in line first.
Calcium sulphate( Gypsum) Ca23% sulphur 17%, which is allowed in organics, will help your sulphur and calcium issues. When you raise sulphur, the ph will lower. thats why gypsum is an excellent source. I believe Bio- ag would have it.
Thanks for the feedback guys! Our base saturation range from field to field but look something like this: 1%K/27%Mg/72%Ca/0.3%Na in what I consider our ‘worst’ field. I’ll check out these sources of sulphur and do some more reading on base saturations.
On the gypsum front, it is a good fit for supplying Ca and S but I believe it is not effective in high pH soils? I might be wrong - anyone? The elemental sulphur is probably your best bet to help leach some of your Mg out. Reducing Mg will help open up your soils. What is your CEC? But high rates of elemental S are harsh on biology. Elemental S takes a while to release if applied on bare soil (so they say).
Have you done a tissue test? Too often folks focus on soil tests when it’s what the plant can eat that is most important. Soil tests may show low micronutrients and calcium, but that doesn’t mean the plants are not getting enough. A big consideration is how nitrogen is managed. With too much manure or compost around, the soil test matters less and less. The excess N in the system causes plant uptake issues, weeds and pests.
Consider mixing your amendments with compost if possible before applying them - you can likely put less out and get more benefit.
Hi, It’s hard to make recommendations without more details about the soil test itself. Some labs will show base saturation values that aren’t based on the correct formulas for further recommendations. Assuming yours are, generally speaking you’d be slightly high in Ca, excessive in Mg, and low in K.
As for sulfur, common soil tests measure the sulphate fraction, which is the plant-available form. Depending on the time of year the soil test was taken and the level of biological activity, this may or may not represent a deficiency in the total sulphur content of the soil. Organic matter contains a fair bit of sulphur, so soils with good organic matter levels are less likely to need additional sulphur. Sandy soils or soils low in organic matter may need amendment.
The rule of thumb for balancing soils is to address the deficiencies first. In this case, you’re low in K and may be low in S. Potassium sulfate will add both K and plant-available sulphur. The sulphate sulphur in this product won’t build up S levels over the long term - that’s where elemental suphur comes in.
Elemental sulphur will also help drive out some of that excess Mg. When that happens, you’ll see the pH start to drop. pH is the symptom of imbalance, not the problem itself. Hope this helps!