Russia did indeed export grain before communism. In fact Russian grain exports were considered important to the earlier industrializing powers of Western Europe, and Russian attempts during the 18th and 19th centuries to gain trading access to these markets occasionally became international issues (such as Russian access from the Black Sea to the Mediterranean).

Russia's agricultural economy was based in serfdom far later than most other European countries, only ending in the 1860s. After this labor was little better, and was often performed for absentee landlords increasingly looking to international markets. The collectivization of agriculture during the early Soviet era created large, and much more efficient farms. Agricultural reforms that had taken hold in the 19th century in western Europe were quickly (and often brutally) implemented in Russia and the Ukraine particularly. While Russia modernized quickly in the 1920s and 30s, atrocities like the Holodomor (the mass starvation of Ukrainians by Stalin) would later lead to some Communist westerners (such as Hannah Arendt) to condemn him as a totalitarian nearly on par with Hitler.

For further info, check out Gildea's Barricades and Borders for a history of 19th century Russia and the international importance of its grain exports, and Arendt's controversial (at the time) The Origins of Totalitarianism for a comparative overview with Stalin's practices.

Russia was an exporter of grain but unlike other nations like America it did so at the cost of its people. Since grain was used similar to Iran's oil barter system currently in use i.e. it would send grain in return for machinery or other products.

The way it worked was pretty much serfdom with the Tsar taking a tithe of the grain produced by a serf every year. This however often ended in the serfs not having enough food and starving over over the winter months.

The communists maintained the same system (but had abolished and reinstated it for different reasons). Initially abolishing the system as part of their promises on the rise to power, Lenin discovered that Russia literally had nothing else with which to trade for the tool and machines he needed to industrialize Russia. Combined with the civil war where armies were starving on the field, he re-instated the system with the standing order that anyone who resisted would be shot.

The new system was much worse since unlike the Tsar who would take a set percentage the communists would take anything they wanted, often leaving families with nothing at all. Which led to the rise of the Green Armies which fought both the Whites and the communists during the civil war.

After the civil war the farm system changed from the serfs to one of community management where the farmers would work community land for grain to send to the centralized collection which would then distribute it where it was needed. However unlike earlier the farmers were allowed to keep a small plot of land for themselves to grow what they wanted.

A little side-not, around 30-50% of all produce during this period was in those tiny plots despite them being a fraction of the much larger fields they were meant to be working on.

Im not sure what happened post Stalinist era however so I'll leave that to someone else.