# Absolute Basic Soil Sampling



## SCGrassMan (Dec 17, 2017)

So I've read the pinned posts and various other threads, and am left with basic remedial questions I'm embarrassed to even ask.

Do I scrape off the grass from the top of the plug? And do I measure 6" from the top of the grass? If there is root matter in the sample does that matter?

I have a soil probe on the way so I want to take a few samples.


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## iowa jim (Jan 22, 2018)

You scrape off of the bottom of the plug and then replace the plug back in the hole. Most people take there samples at a 4" depth. Try to remove any root material in the sample as it might skew the results. Take your sample from several spots in your lawn and mix them together and let it dry out some before you send in your sample. ( hope this helps )


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## Jayray (Aug 8, 2018)

The city here has a soil scientist on staff and they give this guidance for collecting a sample:

http://www.sccd.org/wp-content/uploads/2015/08/EXT0704-1.pdf

https://www.youtube.com/watch?v=JgBlQViclaM


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## Suburban Jungle Life (Mar 1, 2018)

I wouldn't do it the way in that video. His recommendation is for gardening. Most turf roots don't go much deeper than 4". You can go to 6" if you wish but keep in mind, the results may test lower. The 0-4" would be best but I remove the first 0.5-1" and keep the portion to 4". The top tends to have thatch, grass clippings, granular fert, and other stuff I don't want in my sample. Use a zigzag pattern and collect many samples. Mix them in a clean plastic container. I prefer that to metal to avoid any contamination. I like to dry them a bit and crumble it to make it easier to remove any roots and other organic matter like sticks. I imagine the roots and pieces of sticks can increase the organic matter reading. Well, unless you use soil savvy and they don't measure that anyway... I mix the sample thoroughly and it's ready to send off.

I'm sure gman and ridgerunner have some feedback on this...


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## JWAY (Oct 16, 2018)

I can attest to a difference in results at different depths. Did the second test because I didn't believe the first one could be so low for P&K.

My first test was samples taken at 5-6" and second test was two months later at 3-4".
The shallow test indicated +/- 3 times more P&K than the deep test. Also PH went from 5.8 to 6.4.

Nothing soil amendments were added in between the tests.


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## Ridgerunner (May 16, 2017)

Some perspective:
The Soil Testing Laboratory: There is always some variability innate in the actual Lab. testing of a soil sample. NAPT requires no more than a 5% deviation MAX for a lab to receive PAP certification. The PAP results I've seen have been well within the range for the vast majority of qualifying labs. Any Lab errors, therefor are due to human error or or an equipment malfunction although not catching an equipment malfunction is also a human error. Some labs have better quality control than others, but even the best labs can contribute up to 5% of deviation in results.

Soil Sampling. This is the "rub", the point in the soil testing process of greatest error and variability. The wrench thrown into the works. Improving the odds of accurate/useful soil test results:

First up, taking a sufficient number of soil samples to improve the odds that the sample sent to the lab reflects the totality of the plot to be tested. The more homogeneous the soil, the more likely sufficient sample numbers will result in accurate lab test results for the whole plot tested. Unfortunately, soil is often more heterogeneous than homogeneous. Saving grace for turf is that lawns are usually small areas compared to farm fields, so the soil is more likely to be more homogeneous than not. When taking samples any pro and any astute amateur should be able to easily identify a change in the visual difference between plug samples and will test those areas separately or at least not include them if the area with the difference is small. Ditto with an area of turf that is performing drastically different (more poorly) than the majority of lawn. There have been a number of studies concerning the statistical relationship between the number of samples taken and how likely the number will reflect the whole plot. Most studies have been based on farm fields (hundreds of acres) but a few years ago, I found two studies that were based on 3000 and 3600 square foot plots (more relatable for turf). Unfortunately my links to them are now dead. Basically, fewer than 8 samples increased the likelihood of error exponentially. 4-5 samples resulted in only a 50% chance that the mixed sample reflected the whole plot. At 8 samples, there was a better than 85% likelihood that the sample mix would reflect the plot and each additional sample above 8 would increase the likelihood by only a couple of percentage points. This "likelihood is commonly called the "confidence level." Consequently, at a minimum, 8 sample per every 3000 square feet of lawn should be taken. However, there is an additional parameter to consider in these studies. The range of accuracy (commonly refered to as the precision level). Do the results fall within 5%, 10%, 15% 20% or even 25% of the "true" values of the whole plot? The number of samples increases the confidence level to a great extent and the precision level to a much lesser extent. Higher levels of both levels result in greater likelihood of accurate results. It can also be used in identifying unreliable test results due to a sampling error or a lab error. The following two live links reflect/demonstrate the concepts of confidence level and precision level and their relationship to the number of samples taken.
See Table 1:
http://msuextension.org/publications/AgandNaturalResources/MT200803AG.pdf
See Table 3:
http://www.nrcresearchpress.com/doi/pdf/10.4141/cjss71-023

In addition to the number of samples submitted for testing there are other factors that have significant influence test accuracy:

Second up. Mixing the Sample. Sample plugs should be thoroughly mixed to blend the individual samples into one homogeneous sample to avoid over representation of any one sample in the final test results. Labs only use 10-30 cm or grams of the soil for testing. Remove the top of the plug, the grass blades, the thatchy layer at the top of the plug including the removal the top quarter inchish of actual soil below it. Of course any obvious and identifiable clumps of OM, roots, stems, pebbles and fertilizer pellets/prills should be removed so they do not skew results.

Third up. 0-4" depth for turf. Consistent depth of of sample coring. Nutrient and pH can vary by depth. Variation in depth of sample can affect test results, particularly for year to year comparison if the depth of testing has changed from one year to the next. See @osuturfman 's post in this thread: https://www.clemson.edu/public/regulatory/ag-srvc-lab/soil-testing/pdf/ph-management.pdf Also see: http://www.soils.wisc.edu/extension/area/2006/WolkowskiSampling.pdf

Fourth up. Taking the soil samples the same time each year. Soil pH varies through the year, with soil being less acidic in very early Spring and progressively becoming more acidic by late Fall. Lower pH is also known to make nutrients, especially micro-nutrients more available, albeit to a much lesser extent than the possible change in pH. Not testing at the same time each year adds another avoidable variable to soil test accuracy. In order to compare apples to apples and minimize season fluctuations in pH and nutrients for accurate year to year comparisons to identify changes, it is important to test at the same time each year.


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## SCGrassMan (Dec 17, 2017)

4" from where though, and do I cut off the grass?


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## Ridgerunner (May 16, 2017)

4" down from the soil surface (0-4") Remove the top of the plug. This means the organic matter, this likely will include the top 1/4" of actual soil at the top in order to accomplish removing the organic matter at the top. It's not a big deal, but it will save you a lot of time when your trying to remove all of the organic matter (grass leaves, roots, twigs, stolons, rhyzomes) and fertilizer prills, etc. in the bucket during mixing. 
Here are a couple of YTs showing taking the top of the core off.
See this one at about 1:10




and this excellent one by a guy named John @Ware at about 5:35


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## Ware (Jan 28, 2017)

I'm not particularly excited about spring this year, but that's some greeeeen grass.


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## SCGrassMan (Dec 17, 2017)

Ware said:


> I'm not particularly excited about spring this year, but that's some greeeeen grass.


Damn I love that yard.

Thanks for the videos that gave me what I need.


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## SCGrassMan (Dec 17, 2017)

So I pulled my plugs last night. Honestly the grass and roots pretty much fell off. When it was still in the core puller, I just grabbed the top of the grass and pulled and it came right out. Just in case somebody else goes searching.

I did it at night, and without measuring exactly to 4", so I probably have a bit of variability in the depths. I did take like 12-20 plugs depending on the area (I did two small areas and two large areas)

Going to be sending them all off to the lab today.


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## Shuffinator (May 2, 2017)

@Ware what probe are you using? I just searched soil probes and all i saw were ones $50-$200... What about just a really small hand shovel to get some soil?


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## Ware (Jan 28, 2017)

Shuffinator said:


> Ware what probe are you using? I just searched soil probes and all i saw were ones $50-$200... What about just a really small hand shovel to get some soil?


I forget where I ordered mine. A small shovel would probably work fine - or even a bulb planter or ProPlugger.


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## Dave (May 5, 2018)

$20 and works well. 
https://www.forestry-suppliers.com/...3231&itemnum=76971&title=Tubular Soil Sampler


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## Bermuda_Newbie (Jun 15, 2018)

Dave said:


> $20 and works well.
> https://www.forestry-suppliers.com/...3231&itemnum=76971&title=Tubular Soil Sampler


Do you think it's possible to find this at a local hardware or irrigation store? I don't want to pay $5 for shipping but I'm gonna need one of these.


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## Shuffinator (May 2, 2017)

Dave said:


> $20 and works well.
> https://www.forestry-suppliers.com/...3231&itemnum=76971&title=Tubular Soil Sampler


You sir, thank you!


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## SCGrassMan (Dec 17, 2017)

I paid the $50 and got the American made one.

So they should have my samples as of yesterday, let's see what they say!


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