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Soil Test Results - what to do?

Posted by jockewing 9a S. Louisiana (My Page) on
Thu, Aug 1, 13 at 12:01

According to my county/parish soil survey, I have "Stough" series soil type which is classified as a poorly to moderately well drained fine sandy loam. This is in St. Tammany Parish just north of New Orleans, LA. I am surprised it is classified as loam--the top couple inches actually isn't that bad--it crumbles nicely. But a shovel's depth down and you run into huge blobs of slimy, greasy, pale gray anaerobic clay. My front yard drains pretty well, but at times my backyard turns into a slimy muckhole. Don't really understand why there is such a difference as the lot is really only about 150 feet deep. Unfortunately, the only place with enough sun to grow roses is smack dab in the middle of the back yard.
I ordered a soil test from Dr. Good Earth and the results are:

pH - 4.7
Organic matter - 1.7%
Phosphorus - low at .8lbs per 1000 sq ft
Potassium - low at .8lbs per 1000 sq ft
Calcium - low at 20.8lbs per 1000 sq ft
Magnesium - low at 2.8lbs per 1000 sq ft

The type of trees that proliferate here are water oaks, live oaks, sweetgums, tallow, and slash/loblolly pines. Most people use either centipede or St Augustine grass and only rarely do you run across a really lush lawn, and even then you never really get that nice deep color.

I have a small plot in the back that was used as a tomato patch in the past that I have amended over the years with bags of top soil, pine bark, grass clipping, manure, etc. The soil there has turned black and most of the big clay blobs have disappeared. There can be as many as 12 giant worms in every shovel turn. I am taking that spot over for my roses and enlarging through sheet composting.

This will take care of my drainage/texture problems and organic matter percentage, but what is the best way to improve my phosphorus, potassium, calcium, and magnesium, and especially how do I properly raise my pH? I will be growing mostly hybrid teas on fortuniana rootstock.

I also want to try to get rid of this "muckhole" effect when there is a lot of rain (we had almost 11 inches this July) and I feel like the soil just drains poorly due to the subsurface clay. Is there something I can do to gradually improve the drainage? I have already raised the lowest spots with fill sand, but I still feel like the water just doesn't seem to drain into the soil well.


Follow-Up Postings:

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RE: Soil Test Results - what to do?

Sounds like your yard straddles the edge of an old lake, pond or swamp and the clay is the old bed. That's a localized condition that won't necessarily show up on soil maps. How deep is the clay? If by chance it's only a few inches thick and there's silty sand underneath, you could dig holes through it and fill with sand to promote drainage. Other than that you kinda have to build up.

I'll let others jump in here on the soil test results.


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RE: Soil Test Results

Actually just taking a quick look at your test results, yikes!

Looks like the Ca:Mg ratio is 10:1 which I think is quite high, suggesting that you should not use regular calcitic lime. Dolomitic lime (with Mg) is what you want.

Organic matter should be more like 5% so you can add lots of compost. This will help with NPK levels as well.


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RE: Soil Test Results - what to do?

Driven through St. Tammany Parish many, many times. You have a very similar geography (low, flat and wet) as where I am, 50 miles south of Houston. My guess would be that you're ~ 25 feet above sea level? However, from your soil test results, your soils are about as opposite of mine as can be.

Your description of your soil is very consistent with the Stough series description. It is noted as being very strongly acidic, and below about 8" indicates signs of frequent or typical anaerobic conditions, probably from the high natural water levels.

You have a couple of distinct issues, one being drainage, the other being the soil test results.

On drainage, given your geography and the natural soil water levels, there probably isn't much you can do to improve soil drainage via percolation directly - the underlying soil is what it is. If you pick a spot for a bed an amend it you can improve the local drainage, until the surrounding and underlying soil stops it , then your improved bed becomes the "bathtub" of sorts. You may be able to help your situation out a bit by re-evaluating the lot grading and surface water flow in high rainfall periods.

For a gardening situation your better bet would be a raised bed, with enough depth that the underlying poor drainage won't be a problem. Doing that you can construct the soil in the bed to be what best suits your needs.

As for your soil test, I'm curious why you chose Dr. Good Earth rather than the LSU Ag Center lab? Did the sample come from just the bed area, or is it representative of a broader view of your landscape?

If the results are representative, the very low pH helps explain the low Ca and Mg levels. My thinking is focus on correcting the pH using dolomitic limestone, which should take care of both Ca and Mg, then retest. The amount is dependent upon soil type, and this is where the LSU AG Center and the local extension service can be a great help with a specific recommendation, but it will probably be something like 100 lbs per thousand square feet.

With the pH corrected, the P and K levels can be supplemented via common fertilizer options, or using organic amendments. Of course if you build a raised bed, that will likely be different soil.

With soil like that it would probably be worthwhile to test the soil broadly, if you haven't already done so, and working to get the pH toward ~ 6.5. For any future tests I would encourage to use the LSU labs, as they have local knowledge, can guide you on appropriate amendments and amounts to use. I would also encourage you to add the micronutrient test in the future. I suggest that because the Stough series description notes a lot of variations in both iron (Fe) and manganese (Mn) concentrations.

Here is a link that might be useful: LSU AgCenter Soil Testing

This post was edited by TXEB on Thu, Aug 1, 13 at 20:52


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RE: Soil Test Results - what to do?

Is your drainage issue the results of a high water table, rather than the clay? Can you dig a hole and find it filled with water? My experience in that area is that the water table is quite high so your best option is raised beds.


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RE: Soil Test Results - what to do?

St. Tammany Parish averages about 40-50 feet above sea level, from lows around 5-10 feet around Slidell in the SE, to about 100 ft ASL in the NW; Covington is about 35 feet ASL. The Parish borders Lake Pontchatrain, overall is about 25% surface water, and they get on average a bit over 60 inches of rain per year. It is basically a settled wetland between the Tchefuncte River basin on the west, the Pearl River basin the east, and the Lake on the south.


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RE: Soil Test Results - what to do?

Yes, I definitely used raised beds. The house itself was actually built on top of a raised mound of fill (those several inches were the difference in Katrina - i didn't flood while neighbors did). So around the house itself, the soil is looser from the sand and the foundation plantings have decent soil.

I sampled from about 6 different spots all around the yard. I am in Slidell area and I think am somewhere around 10 feet above sea level. The water table is high here. However if I dig a hole it does NOT automatically fill up with water. I dug a hole in the area in my backyard that gets the muckiest when it rains. I filled it with water and it all drained out within 3 hours. However a few weeks ago we had several days where it rained in excess of an inch each day and at that time the hole did not drain for several days.

My actual planting beds will definitely be raised, but I still wish there was a way to get the lawn and bare areas to drain better. Last night I applied about 50 pounds of dolomitic lime per 1000 sq feet to start to take care of my pH and calcium and magnesium deficiencies. It was recommended I need as much as 150 pounds per 1000 sq feet, but it was recommended to not put more than 50pounds at once. How long should I wait before the next application?

What can I do to improve the soil in the lawn areas? If I could do it all over again, I would amend the soil before planting the grass, but that wasn't an option when i bought the house 12 years ago. The first 2 years with new centipede sod the lawn looked like a putting green -- it was lush and beautiful. But it has continually decreased in quality each year.

I complain about the drainage, but I have a flourishing Parkinsonia aculeata tree in the spot along the back fence that turns into a swamp when it rains. That tree is really a tree for arid climates but it grows like gangbusters in this wet spot so maybe the drainage isn't as bad as I think?


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RE: Soil Test Results - what to do?

Slidell area, huh? Got crawfish?

Overall it sounds like your drainage isn't all that bad, except for flooding rains. About the only option you have for overall drainage are grade for runoff and possibly a drain system (tile - French drain, or surface drains) if you have someplace that you can legally direct the flow. With either, you need to be cognizant of local codes/ordinances about changing drainage and permissible discharge (in TX it is a major faux pas to change your land grade in a way that alters the drainage on adjacent lands, and in our town we can only drain to the street).

For your lawn, getting the pH and basic nutrients right, along with trace elements (iron in particular) will help a lot. Since your grounds tend to get and stay wet, core aeration may help overcome the anaerobic tendencies that comes with soggy soils a good bit . If you go the core aeration route then topdressing with some good compost immediately afterwards may help as well.

Limestone takes time to work. It really depends upon moisture, soil type, and the magnitude of the change. I would guess with as acidic as your soil is for a start, that with average rainfalls of ~ 5"/month, wait 2-3 months then test again, so mid-October. At that time do the micro test as well - using the LSU AgCenter lab I believe the combination of Routine + Micro will run you about $15. With those results you will still have plenty of time to make a second addition and plan to correct for any micro deficiencies before the start of spring growth.


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RE: Soil Test Results - what to do?

We have a drainage ditch that runs along the street in the front yard. The low spot in my front yard I dug a french drain that drains directly in the ditch. Now that spot drains beautifully in a matter of minutes. I would love to put some drains in the backyard too and tie into that existing drain line, but that is a long distance to the backyard and seems like it would be such a hassle. Maybe I should just bite the bullet and do it. I just wonder though about the grade. Coming all the way from the backyard, would it still flow out to the ditch in the front? Where I live is pretty much as flat as can be, so there can't be more than a couple inches difference in incline in any area of the yard. I supposed if the drain is underground, as long as the exit point is at a lower level (into the ditch) the drain will function properly? I suppose it is about 120 feet or so from where the drain in the back would be to the ditch at the street in the front yard.


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RE: Soil Test Results - what to do?

You might want to consult with a good landscape contractor who does drainage. There are many options, the question is which is best for your specific conditions. My buddy across the street only has 8" of fall over 200', not enough for a natural flow drain, so he has a sump - he has drain basins in low areas around the edges that route to the sump, and then the sump is pumped to the daylight opening at the street.

Local knowledge, experience and eyes on the specific project are often worth the added cost.


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RE: Soil Test Results - what to do?

Where your water table may be has little to do with your height above sea level. I am around 690 feet above sea level and the water table here, depending on numerous factors, ranges from at the surface of the soil to a few feet down. Water flows under our feet all the time, if it didn't those of us that depend on wells for water would not have any.


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RE: Soil Test Results - what to do?

  • Posted by glib 5.5 (My Page) on
    Sat, Aug 3, 13 at 23:23

This type of soil can take unlimited amounts of wood ash. Whoever you know who may have a wood stove, give them a bucket to fill. This will optimally fix your pH, your Ca, your P, and your K (as well as a number of other micronutrients). For example the P/K ratio is about 1/3, which is what you want in good soil. Wood ash is about 50% Ca, with a pH of 10.4.


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