Dear Joe--
I am pretty sure that Gary Fick's Ph.D. dissertation on sugar beet growth
simulation includes sbeet root weights.  The dissertation was published
in 1971 and was titled "Analysis and simulation of the growth of sugar
beet (Beta vulgaris L.)", out of UCDavis.  Fick's middle initial is W.
This work was published as some articles too, but the details are in
the dissertation.  I used his model for my Master's thesis at UCLA, but
those materials are in a box in my basement now.  I conclude by saying that
even though the work is 25+ years old, one of Fick's contributions besides
the simulation efforts was to gather detailed data about sugar beet root
properties and growth rates, etc.  Hope this helps , even though it
isn't one of the main crops you were interested in.
 
        Sincerely,
 
        John T. Hayes
        Dept. of Geography
        Salem State College
        Salem, MA  01970