if I have clay content :
Clay (0-10cm of soil depth) = a %,
clay (10-20 cm of soil depth) = b%
what is clay content at 0-20 cm of soil depth?
is it average of a and b
You can't do that way economically...unless you delineate through diagnostic horizons .
Averaging may only be done if the studied soil depth is homogeneous with respect to horizonation. If there are distinct soil horizons then measure precise depths of individual horizons and their respective clay contents. further, calculate "weighted average" instead of "average". The weights will be horizon depths and values will be clay contents.
Google for additional information on how to do weighted averaging.
MKD
The weighting parameter you must use in heterogenous soils is the soil bulk density, Pb. Soil bulk density relates to the mass over volume of soils. Soils at surface have usually smaller bulk density values than soils beneath due to ploughing, trafficking, etc. Then, very simple, multiply ((a%*Pba)+(b%*Pbb))/(Pb(a,b).
Kind Regards
Jose Navar, Ph.D
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