Ask a Question forum: Soil test results... what do they mean?

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Long Island, NY (Zone 7b)
Apr 28, 2017 5:27 AM CST
I had 6 yards of "garden soil" delivered for 2 large raised beds that I'd built. I wasn't happy about the soil: very sandy, and it looked poorly screened. So I brought a sample to the local agricultural extension and sent a sample out to the lab they use.
They did a pH and bolus test at the office. pH was 7.8, and the wetted sample felt gritty and didn't form a good ball (not very cohesive and couldn't extrude a ribbon).

I also just got back the nutrient analysis:
Phosphorus (P): 72 lbs/Acre
Potassium (K): 1665 lbs/Acre
Organic Matter: 13.4 %
Soluble Salts: 1.7 mmhos/cm

And a note that "You will need a total of about 3.5 ounces of nitrogen for every 100 square feet of garden for the entire year." I.e., that amount to be distributed over a year.

On the one hand, from what I've read you should lower pH using compost. But I have 13.4% organic matter; according to this:
"Sandy soils with an organic matter content of 2-2 1⁄2% and clayey soils with 3-5% organic matter will perform fine. Organic matter levels twice this amount could lead to nutrient imbalances." My soil was described as loamy sand, so I presume it has way too much organic matter already. Am I reading this wrong? Do I need to turn to sulphur compounds to bring down the pH a bit?

Just HOW high are those P and K numbers, compared to a normal range?

The analysis also said, "Soil P level is very high, so no additional P is needed. However if you are planting into cool soils, transplants may benefit from a starter solution high in P. This will help plants recover from transplant shock."

Does this mean a solution applied to the transplants at the time of transplant, or some time before, to prepare them for the high levels?
[Last edited by Scott_R - Apr 28, 2017 6:28 AM (+)]
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Name: Sue
Ontario, Canada (Zone 4a)
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Apr 28, 2017 8:17 AM CST
To answer the pH question, it depends on what you want to grow. It's a little high for some plants. Compost is not guaranteed to lower pH so you could use sulphur if you want to bring it down. The organic matter will reduce itself over time as it decomposes further.

You should ask them to recommend how much sulphur to use based on your soil test (because it will vary depending on how much you want to lower it and what the buffering capacity is of the soil - sandy soil would need less to lower the pH than a soil with clay and/or organic matter).

I think what they mean by a starter solution is a liquid fertilizer that is high in P watered in when you plant if the soil is still cold. You might want to take the soil temperature because when I checked it here yesterday it was 52F under turf. I had expected it to be lower, we had snow about two weeks ago.
[Last edited by sooby - Apr 28, 2017 8:18 AM (+)]
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Long Island, NY (Zone 7b)
Apr 28, 2017 9:08 AM CST
I don't plan on doing much if any planting for about a month or so; it just sounded odd to me to be adding more P to soil that was already high in it, so I thought maybe it meant add to the seedlings a few days before transplanting, to acclimate them.

And the soil they delivered has the strange combination of being both sandy and high in organic matter--I presume the latter hasn't broken down well yet.
[Last edited by Scott_R - Apr 28, 2017 9:09 AM (+)]
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Name: Sue
Ontario, Canada (Zone 4a)
Daylilies Birds Enjoys or suffers cold winters Native Plants and Wildflowers Butterflies Annuals
Region: Canadian Keeps Horses Dog Lover Plant Identifier Garden Sages
Apr 28, 2017 10:02 AM CST
I would ask them what they meant but, especially if you aren't starting for a month or so anyway, I wouldn't use it where P is already high. While not exactly your situation, you might find this article of interest:

"In Pennsylvania, especially on farms with livestock or poultry, having high and sometimes very high P soil test levels is becoming more common. The use of P containing starter fertilizers on these high testing soils has been questioned both regarding the necessity of P in the starter and the potential environmental impact of adding P to soils that are already high in P. Recent research has shown that in some instances there is a benefit to adding starter fertilizer for corn even on high testing soils. However, this benefit is seen only about 20 percent of the time and the size of the response, while significant, is usually relatively small."

From: "Starter Fertilizer"
Name: Baja
Baja California (Zone 11b)
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Apr 28, 2017 11:39 AM CST
It sounds like whoever sold you the soil started with some very sandy soil and mixed in some organic matter to compensate. Maybe? We have very sandy soil here (ancestral river bottom) and I mix in a huge amount of compost (by the above standards) whenever I install plants. Like 25% of the final volume, maybe more. I have never gotten a soil test so I'm speaking only from tweaking and monitoring the results. I'm sure your mileage will vary depending on what kind of plants you want to grow, but I would not be afraid of mixing in more compost, knowing it will gradually percolate down out of the raised bed into the ground below over time. To target the pH more specifically the sulfur should work, just try to use the right amount (which should not be too hard given you already have the volume and pH).
Long Island, NY (Zone 7b)
Apr 28, 2017 12:53 PM CST
The ag extension office wasn't impressed by the soil I brought in... the people who did the pH/texture test, I mean. The woman had an almost apologetic look on her face as she told me it was basically coarse sand with organic matter mixed in.

I'm in-process of removing the top layer (to be used elsewhere to fill/level areas) and putting down some good soil in its place. I'd read that tomatoes can put down roots pretty deep, so I want to remediate that lower level somewhat, too. My understanding is that tomatoes like their soil more acidic than what I have, so I'll try to bring down that pH and add some nitrogen.
[Last edited by Scott_R - Apr 29, 2017 12:12 PM (+)]
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