...You can't
"Switching off" Barracks is of course first good action to limit the problem.
Building a seaport on those coastal grain-producing provinces (if any) also helps a little (beware: seaports increase oil consumption).

Next steps are:
- build level-1 infratrastructures in grain-producing provinces: infrastructures increase production. Same effect of the industrial complexes, but infrastructures have lower cost and faster completing time. Level 2 ans 3 start to be more expensive.
- then build industrial complexes also: they too increase production. Level 1 is more expensive than Level 1 infrastructure, but from Level 2 on, construction costs decrease a lot.
- Message your allies (or other players) proposing them resource exchanges: offer them the resource you produce with higher rate in change of their grain ("new trade" button in the in-game messaging interface).

...Once you have grain production back in positive trend (green data), you can "switch on" barracks (do it gradually...) and continue your army's build-up

Just don't conquer areas that you don't need to win.

Yeah, as @Piccolo_Legionario said, the best thing is building infrastructure. Level 3 infrastructure can increase the province production up to 50%. I wouldn't recommend harbours, 'cos they just eat up your oil.

if you need the resource and a production advantage try to invest on industrial complex on grain province, this way you not only increase income significantly but have the advantage of numbers (considering you can maintain it)

don't attack recklessly and try to target enemy grain province, and lastly use tanks as a vanguard force since they consume less grain but have oil upkeep.

I thought i knew things... i clearly didnt. INFRASTRUCTURE INCREASES PRODUCTION? time to mass build (Also i have question, in wars does the population take casualties? like form rockets?)

No need to revive old dead and most important outdated thread.
"Call of war - classic" has productionsbonus for Infrastrukture. Common call of War has not.

Please close this one.

Wow, never realized how old this thread was.

2015!??????????

This is probably one of the first threads.

Have you seen the first criticism thread? they talk about how adding carriers is going to break the game.

WHA??

Can we have this 2015 thread closed please.