RETC outputs

[Sara Vero]

Hi,
I was wondering if anyone could help me. I have a collection of data for various soil profiles which I intend to run through Hydrus. Data includes textural information, bulk density and water retention as determined using the pressure plate method. I ran the data through RETC twice; once in which I used only textural and bulk density data, and once in which I included also the water retention data. I expected that the results of the retention data batch would differ from the texture/bulk density results. However, the outputs were identical. Does anyone know why this is? It would suggest that the accuracy of RETC is not improved by the inclusion of water retention data, but this does not seem probable to me. It is possible that I have simply made a mistake somewhere. Any thoughts would be greatly appreciated.
Sara

[Jirka]

The RETC code fits only the retention data, independently of textural data. Textural data can be used only to provide you with the initial estimate of fitted parameters, but are not used in the optimization. J.

[Sara Vero]

If the results for both the textural only and the pressure plate are identical does that then mean that the values estimated using the textural data alone are accurate? Surely the two should differ?

[Sara Vero]

I tried running the program a number of times using different retention curve data but leaving the textural data unaltered. However, I am still getting identical results for each run. This is despite selecting 'Retention data only' as the type of fitting. I can't understand, as it's as though the program is ignoring the input retention data and using the textural estimate only.

[Jirka]

What you write does not make any sense. RETC is not using textural data when fitting the retention data. J.

[Sara Vero]

I think this may be a simple mistake on my part. Would I be correct in thinking that the RETC outputs I should use as inputs for Hydrus are those listed in the table 'Nonlinear least-squares analysis: final results'?

[Jirka]

Yes. J.