How does one tell where the topsoil ends?

[mundamanu]

I have often come across discussions of projects where the instruction is to "strip off the top soil."

Unless one digs down to bedrock (or a solid layer of clay), how does one determine where the top soil ends? I feel like I can go dig a hole in my field and the composition of the soil won't change for four feet. Obviously this isn't true. I'm just curious what I'm supposed to be looking for.

I have no current ongoing or imminent project; I am just interested to know so that when I do have to "strip off the top soil," I stop sometime before I hear Chinese being spoken.

Thanks in advance.

Bob

 

[rambler]

The topsoil is typically easy to see in farm country. It is where the organic material & critters (worms, bugs, etc.) is mixed in with the 'regular' soil. In an undisturbed forest soil, it is pretty shallow, a couple of inches. In a prairie soil when they farmed in the last 100 years, it is typically as deep as the plow went - 6-8".

If you dig a hole a couple feet deep & make a vertical wall & brush it off so it is pretty smooth & not contaminated with your digging, it is often very easy to see a distinct line where the topsoil ends & the subsoil starts.

In peat ground (muck - bottom ground) all bets are off, that stuff can go 4-6 feet deep. Also disturbed soils, if your land was filled in or if water floods it freqently (but you won't be building on a flood plain), then I don't know how they classify that as - topsoil really doesn't apply to that, but you often have to put footers in to below the disturbed (hauled in fill) soil for a real building.

--->Paul

 

[CTyler]

Have a well dug and they will give you a report. The topsoil on my farm ground varies from 1' on high ground to over 20' at the bottom near the creek. Had to dig a couple holes /forums/images/graemlins/frown.gif

I could see some of this when digging the septic tanks for the house and shop. The ground turned brown in color and got much harder around 6-7'.

When we built our drive coming down the hill(650'+) we pulled off the topsoil, corn stalks etc.. It was obvious because it went from very dark to a brown color.

 

[Egon]

Topsoil will contain organic matter.

Egon

 

[fishman]

On my property, the topsoil is that 1 inch layer below the weeds and above the bedrock. /forums/images/graemlins/laugh.gif

I'm working on it. /forums/images/graemlins/crazy.gif

 

[Poppa]

Bob, as stated previously, the topsoil is the upper portion of the soil containing organic matter. The depths can vary usually based on the lay of the land. The flatter the land, the more uniform (typically and not including graveyards) the thickness. Here on my five acres I have rolling hills. on the tops of the hills the topsoil is less than an inch thick and very little will grow there. In the valleys, the topsoil is well over three feet and I can grow any variety weed you can name.

When they tell you to "Strip the topsoil" They are doing this for a couple of reasons. Since the topsoil is usually loaded with organics (if you are lucky) it makes a lousy subgrade to build on. It just doesn't compact uniformly and as time goes on the organics will disappear leaving void space. The other reason is that good topsoil is worth it's weight in gold. Usually on any construction project they will strip the topsoil and stockpile for later landscaping use. What you don't want to do is mix it with the underlying soils because then you have what we geologists refer to as "A pile of dirt." /forums/images/graemlins/crazy.gif

 

[mundamanu]

Thank you all for the explanations.

 

[cowboydoc]

The other reason you may not be able to see a difference in your soil is that you may not have any topsoil left. That's why some areas of the country produce 250 bushels/acre of corn and others produce 50 acres/bushel. Good topsoil land that is farmable will go for $3000-5000/acre while land with little or no topsoil will go for $500/acre in the same area.