Soil test results - now what?

gardeningannie(06)April 11, 2014

Seems I can't make a decision any more without consulting my Gardenweb family first !

Just had soil testing completed: Bottom line is no P needed, but suggested I add plenty of N and K. Also powdered sulfur due to a pH of 7.5 in my raised veggie bed and in ground flower beds.

I use alfalfa pellets, soybean meal and Espoma Holly Tone for pretty much everything, but think the high phosphorus levels were a result of my attempt a few years ago to lower the pH with triple phosphate or maybe it was the decades-ago use of 10-10-10 every spring ~ who knows.

Either way, for years now I've strayed away from the chemicals and make my own compost which I use liberally. For this reason, my organic matter is pretty high ~ 14%, so I'll lay off adding more compost for a season,

I applied the alfalfa pellets, SBM and Hollytone a couple of weeks ago (after soil testing results) and as peas and kale went in, but not sure what to look for in purchasing potash and ground sulfur.

Any suggestions for best sources, favorite brands or where to buy? Any precautions when using either of these products?

I noticed Espoma sells a bag of Potash, but can't be found around here. They also have a Citrus formula which is 5-2-6 and Palm formula which is 4-1-5, both of which might give me the added N/K and micronutrients, but doesn't address the sulfur issue.

Look forward to hearing your thoughts !

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Kelp is also a good source of K.

A pH of 7.5 is well within the tolerated range of peas, kale, beets and other veggies in these families, and a little above the range of solanums and cucurbits. To accomplish a more gentle lowering of pH, I'd continue using the alfalfa pellets and SBM (both of which will gradually acidify the soil over time) and add sulfur at the low end of recommended amounts, particularly if your soil is sandy. I use Tiger Sulphur, which is 90% S and 10% clay and the pellets "explode" once exposed to moisture and warmth. Till it well into the soil.

For more quick results and less risk of getting your pH too low, use iron sulfate instead. You should be able to purchase that at a garden store. Iron sulfate heptahydrate has one-sixth the acidifying power of sulfur, but don't apply more than 4 lbs per 100 sq ft at any one time. Till it in.

    Bookmark   April 11, 2014 at 12:23PM
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Great advice and right in keeping with my love of using alfalfa and SBM. You're making this adjustment sound easy

In regard to the iron sulfate, did you mean 4 lbs per 1,000 ?

    Bookmark   April 11, 2014 at 12:55PM
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Nope, 4 lbs per 100, or 40 lbs per 1000 sq ft. In my clay loam with high OM content, this gives me a pH drop of about 0.3 points, but it could be a drop of 0.5 to 0.7 points in a lighter, sandier soil.
If you do use this much, irrigate well after tilling and let it sit for a week before planting anything. A better approach, though, would be to apply 2 lbs per 100 sq ft and 2 lbs again later in the season between crops. Don't apply to an existing crop or it could burn them.

If you are not planning to grow potatoes, watermelons, tomatoes or peppers, I would even avoid the iron sulfate and just continue using organic N fertilizers to adjust the pH.

This post was edited by Slimy_Okra on Fri, Apr 11, 14 at 13:08

    Bookmark   April 11, 2014 at 1:03PM
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Most of the research I have seen, and my own experience, tells me that vegetative waste in soil does not, at least in the short term, significantly affect soil pH. Alfalfa needs an alkaline soil to grow well in, pH above 7.0.
I even added peat moss to a planting bed with a soil pH of 5.7 to lower that so I could grow some blueberries and the next soil test showed the soil pH was 7.2. The pH of tree leaves is in the 3.2 to 3.8 range and the pH of peat moss is in the 4.5 range so if, as my experience indicates, adding tree leaves or peat moss to my soils changes the pH from 5.7 to 7.2 why would I expect any other vegetative waste to do anything else? One professor of soil science I talked with did suggest that organic matter might lower a soils pH over time, like eons, but short term organic matter will raise a soils pH.

    Bookmark   April 12, 2014 at 6:30AM
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High-nitrogen organic amendments (or ammonium-based nitrogen fertilizers) do lower soil pH, albeit in small increments. The process of conversion of proteins to urea, then to ammonia, and finally to nitrate, lowers the pH.

    Bookmark   April 12, 2014 at 11:11AM
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