...Does anyone remember or have source to indicate where the song was learned by Ruth Rubin (who also recorded it in 1947)...

Where does that 1947 record label and release year come from? So far, I have Asch Recordings; Stinson Records & Disc Records all off the same Moe Asch master(s.) Year 1947 might-could work for the latter two but Asch Recordings… not so much. Maybe middle/late '45 or thereabouts. Still checking the Billboard back issues.

The People's Song Book notes (above) are straight from the track notes on 2:3 of the above. In full:
“(Soviet-Yiddish Collective Farm Song – Crimea)

This Yiddish song was composed in the Soviet Crimea within the past twenty years. Zhankoye is the railroad station which centralised a whole network of Jewish collective farms in that area. Note the joy expressed in the new-found occupations driving a tractor, threshing and reaping.”

It being Soviet 'folk' song on an Artkino distributed release should do for its ultimate sourcing. More than just likely there's also some related bit of long-lost Stalinist cinema still out there waiting to be rediscovered as well.