estimate missing dbovendry_r from dbthirdbar_r

[dylanbeaudette]

This is most important for O horizons.

select cokey, compname, compkind, comppct_r, om_r, caco3_r, dbovendry_r, dbthirdbar_r, hzname, hzdept_r, hzdepb_r 
FROM
ssurgo.component 
JOIN ssurgo.chorizon 
USING (cokey) 
WHERE hzname ~~ 'O' ;

Do we even need to estimate? Perhaps use 1/3 bar Db for OM calculations as in these SDA notes on the topic.

[dylanbeaudette]

Using 1/3 bar Db now.