I am not sure by what you mean by operation, but moisture increases bulk density by allowing the soil grains to align and become  compacted more easily up to a threshold that is the optimum water content (maybe around 10%).  After which, the soil becomes less dense.  I would think this phenomena holds regardless of whether the operations by which you refer are occurring. 

If your soils are prone to swelling or shrinking depending on moisture content (as is the case with some clay soils) then I think it may have an effect.

Also, even the best sampling procedure is likely to result in some compaction and thus, changes in bulk density. Whether this could be significant or not however, is probably case-sensitive.

I agree with Sara - the swelling and shrinking is notably significant especially in clayey soil with predomination of montmorillonite (smectite) and in organic soils. In consequence, if we take undisturbed samples (in cilinders) from dry soils (however, it would be very difficult or impossible in clayey soils), the soil will have greater dry bulk density, when the same soil sampled when moist.

Of course it has effect. This is why we need to oven drying the wet soil sample.

It certainly would affect,I would agree with above scientists.

If you have effect, so it is necessary to dry the sample before

I disaggree to the advice to sample from a dry soil.

Aspects of shrinking and swelling (see above) but also of  stability of aggregates suggest to sample soils at a  HIGH soil moisture. Although the concept is discussed, Field Capacity (soil moisture at pF1.8 to pF2.0) is the better (defined) moisture status for soil sampling compared to any dry status (which one btw? pF 3.0? pF4.2?). Otherwise, subsequent analyses (e.g. water retention curves) make no sense.

Practically: the good thing about sampling from wet soil is, that your sample shrinks with drying and still fits to the cylinder. When it swells with re-wetting it will still fit to the cylinder.  Try that with a sample taken from dry soil...

As far as I know, when soil is sampled at below a certain water potential (depending on soil texture) dry bulk density occurs greater than it suppose to be.  The most proper soil water potential for soil sampling is around the field capacity.  

Yes, of course the effect will also depend upon texture, OM and mineralogical make up of soils.

Soil moisture content at the time of sampling does have influence on soil dry bulk density. This is particularly so when you are dealing with soils high in clay content which will encourage compaction of the soils. This also explains why soils have to be oven dried after sampling to remove the water

 The soil moisture content during operation have strong effect on dry bulk density, but in order to compare different  result or extrapolate obtained results we express the bulk density values  of dry soil (keep soil samples 8 hours at 105C). In order to appreciate soil compaction we must, also, take account  size particles. The same bulk density value of dry soil has one significance  when soil is sandy and another if the soil has high content of clay. For soil compaction evaluation is possible to use packing density values.     

Dear Filipov Feodor

Thanks for your answer but I asked a question about effects of soil moisture content during sampling on soil bulk density, Not during operation.

Yes, of course soil moisture during the sampling and property sampling has a great effect to bulk density. As prof. Ersahin wrote "The most proper soil water potential for soil sampling is around the field water capacity" and also as Mr Ghafoor wrote (the value of bulk density), the efect will also depend upon texture, organic mater and mineral make up of soils.

 Soil moisture content during sampling have effect on dry bulk density, but finale results we   are rendered by reference to dry soil.

It is well known tat soil the soil sampling must be done on the certain interval of soil moisture. If the soil has fine texture and is too dry, we can observe the crakes  result after soil contraction. If the soil is too wet, after swelling processes, the volume increase simultaneously with decreasing of bulk density values. Recommended moisture   for soil sampling is between field capacity and lower limit 1/3 or 1/2 between useful water capacity. 

My point of view, if you can draw soil samples without disturbing it ( in most cases, moist soil tend to compacting, more dry soil tend to loosening), the soil moisture content not effect  to soil bulk density because soil bulk density is expressed as dry soil mass per unit volume. (keep soil sample at 105 C until reach a constant weight).