model-specific variables

[chporter]

From @JeffWhiteAZ : Arguably, the mineralization factor is CSM-specific. Should the ICASA standards include variables that aren't easily measured and thus really aren't used to document an experiment?
Another example is the root growth factor, SLRGF. We should be asking for the NRCS assessment of roots, and then have DSSAT users convert to SLRGF. There may be other variables, but this seems mainly like a soil properties issue.

[chporter]

Also SDATE.