Lawn Care Forum banner

First soil test results

2504 Views 22 Replies 5 Participants Last post by  Ridgerunner
Hey guys, I received my first soil test results. Any help on deciphering what it means, and your guys thoughts on it would be appreciated. Thanks

See less See more
1 - 6 of 23 Posts
@Jeaux Bleaux
Welcome to TLF.
LSU uses Mehlich 3 for testing and reports values for each nutrient in parts per million (ppm).
Ideally you will want to have your test reported values to fall within the following M# ranges (realistically, with a fine sand loam, your "target" should be somewhere between the middle and the low end of the ranges):

M3 Ranges (in ppm)

P: 26-54
Ca: 500-750
Mg: 70-140, 60-120 for sands
K: 75-176, 50-116 for sands
Na: unreported/N.A.
S: 15-40
Fe: 50-100
Cu: 0.4-2.5
Zn: 1-2
Mn: 4-8, 8-16 for pH >7
B: unreported/N.A. (update: per PACE and R. Carrow: 0.4/0.5- 1.5)

To calculate what nutrients and how much to add of each nutrient read the Simple Method on pg 4:
Feel free to post any questions that arise.

Regarding pH, anything between pH 6 and 7 is very good. Your back yard is below this range and you will want to raise it. Per the LSU report (titration w/1T equivalents method), adding one ton of lime should raise your pH to 6.7.
To determine how many pounds of lime per one thousand square feet, divide 2000 by 44 (there is about 43,560 square feet in an acre). That works out to 45lbs of lime per thousand square feet, but a pH of 6.7 is a bit on the high side and the LSU calculation is probably for changing pH to a depth of 6.7 to 8". To be safe (it's easier to raise pH than lower it). I'd suggest you apply only 25 lbs of lime this year and see where your pH settles out on a soil test next year.
See less See more
kur1j said:
@Ridgerunner Is the Ph change only temporary?
Yes. How fast and how much of a return to a lower pH will occur will depend on a number of factors such as: climate/rainfall/irrigation/leaching/soil texture, CEC of the soil and type and amount of N fertilizer applied.

If nothing else is really done will the Ph change drastically over time?
Not sure if this is what you are asking, but: With the exception of a peat bog for instance, most undisturbed native mineral soils of the world will have a pH between 4 and 9. This is a result of rainfall/leaching, type of parent material of the soil, and OM decomposition. I would think that if left undisturbed for millennia, these factors would have found an "equilibrium" and pH would remain relatively constant.
Just as an example. I live in Ohio. I have sandy silt soil with a CEC of about 10. Average annual rainfall is 38".
I applied 5-7 lbs of urea/M in most years, plus Milo. In six years my pH has lowered 0.4 from pH 6.5 to 6.1.
@kur1j Ahhh. I was going to mention that but thought it was TMI. Yes, pH can drop up to 1 full point between Spring and Fall due to OM decomposition and N fertilizer application then raise over Winter as H+ is removed from the soil solution during cool temperature rainy months. This is especially pronounced in low CEC or sandy soils in the South. It's one of the reasons why soil testing should always be done in the same month from year to year.

Edited phrasing for accuracy and clarity.
viva_oldtrafford said:
kur1j said:
@Ridgerunner I've did 2 soil tests last year. One around April/May last year, and then another in late summer (Sept).

The April/May Soil test showed I had pH of 6.42. The one late in the year showed I had a Ph of 5.9. So in a matter of 6 months my Ph. dropped .5 which is the reason I asked how much it can change.

I had a local lawn care company doing my "weed" control (it came with house) and they applied Lime in December. I just sent off another soil sample test today to see where I'm at with things. From my understanding, this clay soil is generally acidic and doesn't hold onto nutrients very well at all. The only positive to it is that it holds moisture really well. Even though I was doing 19-19-19 1lb/1k a month every single test came back low on my P and K. April had a recommendation of .7lbs/1k of P and K (it was a generic recommendation of 3.75lbs of 16-16-16 per 1k). The second soil test I did came back with a recommendation of putting down 1.95lb1/1k P and 1.61lb/1k.

I'm interested to see what this new soil test comes back with. If everything is low...I'm going to up my fertilizer rate. But I digress. I don't want to hijack this post any more than I already did.
Clay is great at holding nutrients...for the same reason it is great at holding water, it is negativley charged - water is polar and the cations are + charged, so they stick to clay very easily.

@ridgerunner would OM decomposition really factor into pH adjustments so quickly, especially in a turfgrass envrionment? Sure, OM decomposes, but as long as there's healthy sward, OM is accumulating at an even faster rate (why we see %om in soil tests always increase and not decrease). 1 full point is a ton...using an acidifying fert? Sure. OM degradation leading to a point drop (logarithmic measurements here) seems a little much.
I wouldn't say that the effect of OM decomposition should be a factor in determining pH adjustment. However, I do think it plays a role in understanding soil pH and in particular, seasonal variations.

Some housekeeping, background and ground rules. Although I've read quite a bit and done a fair share of analysis, I'm still just a layman:

1. The seasonal variation of as much as 1 full point of change in pH stems from my readings while researching proper soil sampling for accuracy and the determination of soil amending based on the soil test results (sources would have been articles by/in crop agronomy, golf soil specialists, and test laboratory advisories--I will see if I can find one in my bookmarks). Although a change of a full point is evidently possible, I think it is the exception and not the rule. Most likely the pH of turf grass soils would vary seasonally in the 0.3-0.5 range.
2. I can't say whether or not changes in soil salt content has been eliminated from the seasonal fluctuation measurement of pH that have been reported. However, salt content interference with the instruments used for measuring pH and skewing results isn't the only influence salt content has on soil pH as some articles state that as soil moisture content falls, salts will displace H+ from cation sites which in turn lowers soil solution pH, an action that will reverse when soil moisture increases.
3. Although I agree that acidifying N fertilizers would be responsible for the lion's share of seasonal change in pH, nitrification of OM would likely not be insignificant albeit highly variable. The climatic influence on OM decay is often cited as the reason that the soils of the Southern U.S typically have low OM percentages compared to those found in soils of the North.
(Going off on a tangent: So OM (stable organic matter/humic substances) can remain in soil for centuries, possibly millennia, because it is resistant to decay, yet it is not impervious to decay depending on climate and microbe activity. More specifically, stable OM is humic acid, fulvic acid and humin. What is it about HA, FA and humin that makes it so resistant to decay? Apparently humin is is an intractable, insoluble, waxy, very decay resistant organic substance within which HA and FA are interspersed. A few soil specialist have surmised that humin acts as the hard candy coating that protects HA and FA from decay by microbes. If accurate, how long do the HA and FA amendments we add survive in the soil without the humin shell for protection?)

The important take away is that for non-alkaline soils, it is very likely that there may be significant variability in pH over the growing season. Consequently, it is advisable to sample the same month each year.

Regarding clay, CEC and moisture holding capacity. Beware of the false logic trap. For instance, It is accurate that sands have low moisture holding capacity. It is also true that sand has low CEC, and most of the time a soil with low CEC will more often than not be a sand, but not always. Highly weathered clay (e.g. kaolinite) like those of the Piedmont soil region that runs along the eastern side of the Appalachians from Virginia to Alabama can have a CEC less than 5 even though they still are classified textural clay. Consequently, they are unable to hold large amounts of nutrients like other clays. However, due to their texture and low bulk density, the resulting vast number of very small spaces between particles makes for high moisture holding capacity like most any other clay.
See less See more
I did find this in my bookmarks.
Soil pH changes seasonally. Higher soil pH
or lower acidity is measured in late winter or
early spring before fertilization. Soil pH can
decrease more than 1 unit (for example, from
7.2 to 6.2) from spring to fall in sandy, low-
organic-matter soils. In areas of low rainfall,
soil pH is lowest or most acidic as the growing
season begins. Soil pH is lowered by fertilizer
application and by the increase in biological
activity as soil warms.
Soil buffering capacity determines the extent
of seasonal pH changes. Soils with substantial
amounts of clay and/or organic matter are buff
ered against pH change and are likely to have a
small seasonal pH change, about 0.3 unit. Soils
with relatively little silt, clay, and/or organic
matter, and a pH below 7.5, can change 1 to
2 units. Soils containing carbonates are buffered
against pH change and will not have as large a
seasonal difference.
1 - 6 of 23 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.