> Natural gas is a commonly used as a feedstock to produce two nitrogen-based fertilizers – ammonia and urea – in large quantities.
> In the production of ammonia or urea, natural gas is processed at an upgrading plant together with nitrogen (taken from the air). During the process, 80% of the gas is used as feed¬stock for fertilizer, while the remaining 20% is used for heat and electricity production. The two main end products, ammonium nitrate and urea, are then mixed with other ingredients—mainly phosphorus and potassium—to manufacture a range of synthetic fertilizers for use on farms.
Now that Russia is the world's biggest wheat producer, it seems that Russian food will be neither scarce nor expensive. And also seeing that it produces a good proportion of the world's fertiliser, it seems that food grown elsewhere will be scarce and expensive.
They'll be fine, I expect no prolonged famine, if any. Population growth will continue as expected. Ignoring western sanctions in exchange for food is a good idea if it comes to that.