# Soil sampling depth



## reede (May 17, 2010)

What are y'all's thoughts on appropriate soil sampling depth? I'm thinking permanent, perennial fields, either hay or pasture. Tillage only at establishment, so not a regular part of the process. You hear of different depths for different things, just thought I would see what folks here do, or think.

Thanks.

Reed


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## Vol (Jul 5, 2009)

My soil sampler(plugs) only goes to a depth of 6 inches which is probably all you need for testing most forages.....alfalfa sampling/testing deeper can be useful.

Regards, Mike


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## somedevildawg (Jun 20, 2011)

I used to go only as deep as the soil probe would go, but I made a 5 gallon bucket with a hole in the bottom and use a cordless drill on a 1" auger bit and drill down about 10"-12", probably only getting the top 8" or so....


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## hillside hay (Feb 4, 2013)

somedevildawg said:


> I used to go only as deep as the soil probe would go, but I made a 5 gallon bucket with a hole in the bottom and use a cordless drill on a 1" auger bit and drill down about 10"-12", probably only getting the top 8" or so....


I started using your method. Saves a lot of time. I run about to 7 in


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## qcfarms (Dec 14, 2014)

I was talking to our OSU Extension Folks this morning on that very subject. They say go no more than 6". That is the depth that they use for all their trials.


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## Vol (Jul 5, 2009)

somedevildawg said:


> I used to go only as deep as the soil probe would go, but I made a 5 gallon bucket with a hole in the bottom and use a cordless drill on a 1" auger bit and drill down about 10"-12", probably only getting the top 8" or so....


Do you use a old wood boring bit or something else?

Regards, Mike


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## r82230 (Mar 1, 2016)

I am 100% no till, use bucket with portable drill (see attached site), 4-6 inches. Nature has to take what ever I put on top deeper, so if it is missing on top, I need to fix that first.

http://www.collectngonow.com/

Larry


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## reede (May 17, 2010)

I'm using a ship auger(woodboring) bit, and my depth question stems from a conversation/visit with my extension agent this past week. He had come up with a modification on the OSU design that includes depth control. I had problems with it plugging in moist soil(it would spin the bucket around, and I couldn't hold it now matter how I tried).

So we were discussing different sampling depths, along with different design modifications to the system. I will share the link to his publication as soon as it comes online. Saw it yesterday, but it will probably get a few format changes before publication.

My pics are next. The basic change he made, is to have one long soil exit hole, where I have multiple holes up the length of the depth tube.

My sampler is set up for a 6 inch sampling depth.







Last picture is of the depth tube. The modification I would make if doing it again, is make one long slot up each side of the pipe. Band saw of milling bit could be used to do this.

The T at the top and short horizontal pipe are for a handhold, to be able to stablilze the tube if needed. I use it to hold the bucket through the whole process, rather than the bail on the bucket itself.

Reed


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## Tim/South (Dec 12, 2011)

I use the bucket/drill also. Bought some large drill bits at a yard sale.

They will plug up sometimes. Just hit them against the side of the bucket and the plugs fall off.

Bits are probably 7 or 8 inches long.


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## mlappin (Jun 25, 2009)

We sample 6-8" deep, use a bulb planting auger in a 1/2" 18volt drill. Ours is a 1 3/4" by 24" auger, just cut a 2" in the bottom of a small pail, place the pail on the ground and run the auger thru the hole, dump the sample into a larger bucket, when you have enough shake the dirt up well to blend it, fill the bag then toss the rest.

Auger loosens the dirt up, so if it's wet and sticky your not trying to fill the bag with turds from a regular probe.


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## qcfarms (Dec 14, 2014)

Vol said:


> Do you use a old wood boring bit or something else?
> 
> Regards, Mike


It is a wood auger bit. Looks like the bit that reede posted in his comments. I just have a hole in my collection bucket and use a battery operated drill with the auger to drill into the soil.


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## vhaby (Dec 30, 2009)

University operated soil testing laboratories base their fertilizer recommendatons on results of field and at times greenhouse fertilizer trials. These trials are designed to evaluate rates of plant nutrients applied and response of various crops to these rates on numerous soils. These soils will have different concentrations of the evaluated plant nutrient. Yield responses are correlated with nutrient application rates and are related to the soil concentration of that particular nutrient. In doing this research, there is a specific soil sampling depth used. Most states use the 6" sampling depth.

As you know, sampling deeper than the soil depth used to develop the fertilizer recommendations will dilute the concentration of plant nutrients that are relatively immobile, such as phosphorus, and result in higher than normal fertilizer recommendations that will cost you money. Sampling shallower that the depth used to develop the fertilizer recommendations will cause an increase in the concentration of the individual plant nutrient, and the recommendation will be for less fertilizer than is needed for optimum yield.

For the standard tests normally done on a sample, it is best to stick with what the laboratory recommends. There are instances where deeper sampling is necessary. Nitrates and sulfates are mobile in the soil, and if a good fertilizer recommendation is needed for these plant nutrients, sampling to deeper depths will be helpful.


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## reede (May 17, 2010)

Vincent,

Some labs, including Clemson here, report soil test results in pounds per acre, while others it is in ppm. I know that the assumption is 2 million pounds of soil per acre. Is the 2 million number based on at 6 inch depth?

Thanks.

Reed


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## reede (May 17, 2010)

So, a little more information on the comparison of 2 depths. When we were testing the soil samplers last week, my extension agent had his set up at 4 inch depth, mine is 6 inches. Results are attached. Some difference, but not as much as I would have thought.

This field is a pasture that will get renovated to rid it of toxic fescue. Spray here in the near future, cover crop for the summer, graze it off, and plant novel endophyte fescue in the fall.

View attachment Field 9 Comparison.pdf


View attachment Field 9, 4inch depth.pdf
View attachment Field 9, 6inch depth.pdf


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## vhaby (Dec 30, 2009)

reede said:


> Vincent,
> 
> Some labs, including Clemson here, report soil test results in pounds per acre, while others it is in ppm. I know that the assumption is 2 million pounds of soil per acre. Is the 2 million number based on at 6 inch depth?
> 
> ...


Yes! The calculation is based on using an average for bulk density of soil- about 1.45 to 1.5.

Multiply these factors:

Weight of water has standard density of 1 and weighs 62.43 lb/ft3

43,560 ft3 /acre

A 6" soil depth equates to 0.5 ft

Soil is heavier than water; bulk density estimated avg. 1.45 or 1.5

With this estimated 2 million pounds of soil per acre 6-inches deep, parts per million multiplied by 2 equals pounds per acre.

Vincent


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## reede (May 17, 2010)

So, concentration of soil "stuff", elements, nutrient compounds, etc.

Concentration in ppm is concentration, no matter what depth you sample to. But, if you sample at a depth different than 6inches, and your report is in pounds per acre, then that number will be off, as will the recommendations for fertilizing/amending the soil.

This stuff gets more fun as you go. But, I like to understand my numbers, not just follow them blindly.

Thanks, Vincent.


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## hcriddle (Jul 5, 2014)

Thanks a bunch guys. This is really interesting stuff and helps me understand how to be a better caretaker of the soil and produce a better product! Much appreciated.


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## reede (May 17, 2010)

Just got the email from my extension agent, the soil sampler publication is now online.

Here's the link:

http://www.clemson.edu/extension/publications/files/livestock-forages/lf11-sweatless-soil-sampler.pdf

Reed


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## Vol (Jul 5, 2009)

A lot of good ag information comes out of Clemson. Pretty handy information from the Clemson Cooperative Extension.

Regards, Mike


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