Dear Ahmad, in fact if you want to compare your results, I believe that you should use the same ring to determine bulk density, no matter which depths you are looking at. You should dig a trench and collect the soil samples using the same typy of ring. It will be very interesting to compare the results from these three depths.

Best wishes,

Antonio Guerra

Department of Geography

Federal University of Rio de Janeiro

BDS is a sound approach and a reference can be fo help http://onlinelibrary.wiley.com/doi/10.1002/jpln.200521845/abstract

Dear Ahmad, in fact if you want to compare your results, I believe that you should use the same ring to determine bulk density, no matter which depths you are looking at. You should dig a trench and collect the soil samples using the same typy of ring. It will be very interesting to compare the results from these three depths.

Best wishes,

Antonio Guerra

Department of Geography

Federal University of Rio de Janeiro

I agree with Antonio Guerra. You can also refer The portable soil core sampler  for gradual sampling of soil profile in the depth up to 0.5 m

http://www.agriculturejournals.cz/publicFiles/52757.pdf

I want to measure the bulk density in three depths (0-10, 10-20, and 20-30 cm). for 0-10 i use from volumetric ring (5 cm of internal diameter and 10 cm of height). Can I measure bulk density in 10-20 and 20-30 depths with this ring?

You  can measure bulk densitiy in 10-20 and 20-30 cm dept with this ring. But firstly, you must dig a profile hole.

Dr. Antonio Guerra, Department of Geography,Federal University of Rio de Janeiro - had already gave the best reply. 

Wish you a great succes

Depth-dependent soil bulk density (BDS) relies on internal factors like mineral composition and texture, and on external factors like water fluxes and compaction. for these reason it is advisable to get to BDS parametric models, as in Jörg Bachmann andKarl Heinrich Hartge literature. with the best

Dear Ahmad,

in addition to what is said, I suggest to reduce the height of the sample (in my opinion, 10 cm height it is a too high sample) and to increase its diameter, in order to prevent soil compaction.

Dear Ahmad, I do agree with Dr. Antonio Guerra. I have collected many soil samples, to determine bulk density and I have followed this method, with very good results. 

Best wishes,

Mrs. Maria do Carmo Oliveira Jorge

PhD graduate student

Deparment of Geography, Federal University of Rio de Janeiro

I agree with Antonio Guerra. The height of volumetric ring may be not 10cm. It is 5cm which I used in my reasearch. However, the volumetric ring should be located at the middle of each soil horizon.

I agree with Antonio Guerra. The height of volumetric ring may be not 10cm. It is 5cm which I used in my reasearch. However, the volumetric ring should be located at the middle of each soil horizon.

You might want to consider to take the soil samples horizontally (instead of the usual vertical way) in the middle of the soil layer you're studying since your ring height is equal to the layer thickness...

Let us know what you did.

Sarah

See the following publication

Core method is the best method to measure soil bulk density

One way we have done this in the past is to take a deep core sample with a giddings probe. You can get plastic sleeves to go inside of the metal tube and easily get cores as deep as 120cm which will remain intact during transport. Then cut the core using a saw and drive your ring into the soil which is in a given area. This of course assumes you have access to a giddings probe or similar device.

http://www.soilsample.com/