# Molecular Biologist in soil lab., problem with soil moisture calculations - (Aug/21/2014 )

Hello There,

I'm wondering if one of my fellow biologists with a Maths brain can help me out. I've been given a new task which is a bit out of my comfort zone.............

So I've been doing DNA extractions from soils but my boss thinks it would be 'nice' to also physically characterise the different soil types we are using. He as sent me a protocol and directed me to a dirty lab where there is no-one around but me and he has now gone on holiday!

So here is the issue. I have lots of soil types but in order to do the analysis the protocol requires me to dry the soil samples out:

'Dry in an oven at 40 degrees Celsius for at least 16h working out moisture loss by taking the fresh weight from the dry weight'. Simple, but then it says 'After drying, the remaining moisture content should not exceed 15% of the total weight'

So how do I work out whether the dried samples contain a moisture content of more than 15% of the total sample weight given that I don't know how much moisture there was in there to start with?

Am I correct in thinking that the only way to do this is to measure the total moisture content of the sample first (I have another protocol for doing this). So if I know the total moisture contained within the sample is 40% (an assume all samples from the same soil batch are the same), I can then work-out from this?

Any pointers or suggestions would be much appreciated,

-phosphate girl-

phosphate girl on Thu Aug 21 09:49:15 2014 said:

Am I correct in thinking that the only way to do this is to measure the total moisture content of the sample first (I have another protocol for doing this). So if I know the total moisture contained within the sample is 40% (an assume all samples from the same soil batch are the same), I can then work-out from this?

looks like a rational way to do it, although, i wouldn't assume anything. i would measure all samples.

-mdfenko-

Its says should not exceed 15% moist.....so why not just "overdry" them till all the moist is gone?

It all depends on what you want to do with the soil...

-pito-

You could probably also find out the average density of a particular soil type, then work it out from there.

-bob1-

I'm working on extraction DNa from soil samples too

but there is no need for drying

also it becomes physically better to use the samples (partially) dried

avoid excessive drying

use temprature less than 55 degree celsius

-Eslam Samir-

For the DNA extraction yes, but she is talking about "o also physically characterise the different soil types we are using." , so I am assuming she does the DNA extraction and then she starts drying the samples for a characterization.

Eslam Samir on Fri Aug 22 22:46:59 2014 said:

I'm working on extraction DNa from soil samples too

but there is no need for drying

also it becomes physically better to use the samples (partially) dried

avoid excessive drying

use temprature less than 55 degree celsius

-pito-

mdfenko on Thu Aug 21 11:35:53 2014 said:

phosphate girl on Thu Aug 21 09:49:15 2014 said:

Am I correct in thinking that the only way to do this is to measure the total moisture content of the sample first (I have another protocol for doing this). So if I know the total moisture contained within the sample is 40% (an assume all samples from the same soil batch are the same), I can then work-out from this?

looks like a rational way to do it, although, i wouldn't assume anything. i would measure all samples.

mdfenko on Thu Aug 21 11:35:53 2014 said:

phosphate girl on Thu Aug 21 09:49:15 2014 said:

Am I correct in thinking that the only way to do this is to measure the total moisture content of the sample first (I have another protocol for doing this). So if I know the total moisture contained within the sample is 40% (an assume all samples from the same soil batch are the same), I can then work-out from this?

looks like a rational way to do it, although, i wouldn't assume anything. i would measure all samples.

^^ I agree with md, this seems like a logical way to go with

-VarianWrynn-