Bulk Density Question

[poonam]

Hello,

I was trying to measure the bulk density of soil samples taken by root auger of diameter 7.5 cm at 2 depths 0-10, 10-25 cm. I did not dry the whole sample for bulk density measurements because I had to take sub samples for other analysis from the same soil. I used the following formula for calculating it but my bulk density values are coming very high. Is someone can tell me whether I am using the right formula or not.

 

% soil moisture=(Wet wt. of subsample-Dry wt. of subsample/Dry weight of subsample)*100

Dry weight of whole soil= (Fresh wt of whole soil/% soil moisture+100)*100

 

BD=Dry wt of whole soil/volume.

 

Thanks,

[CaptainPanic]

Right now you express the soil moisture as a percentage of the dry weight (meaning it can theoretically be more than 100% - which is why it's so high).

 

I would suggest you express it as a percentage of the wet weight (meaning you must divide it by the "Wet wt. of subsample").

 

I'm not sure how you determined that second formula.

 

Dry weight of whole soil = wet weight * (1 - soil moisture)

(That is: assuming that you determined the soil moisture as a percentage of the whole soil, as I suggested before).

 

If you don't dry the sample completely, how do you know how much water is in it?

 

Next time, take two samples (one for bulk density, one for other tests)... I'm not sure of your particular location, but where I live there is no shortage of soil.

 

I think you're making your life unnecessarily complicated. Next time: take a sample. Determine its volume. Measure its weight. Dry it. Measure the weight again. Done.