Crop Production drops to zero

Out of no where, i realised that my crop production drops to 0/hr.
All the other icons seems normal.
What happened? and how to solve the problem.
Help !!!

Thanks

Well, when you have troops, if they're using up more crop than your city is making, you'll either be earning no crop or you'll be in negative.

For each troop you build they eat a certain amount of crop, each infantry eats 1 crop per hour, each cav eats 4 crop per hour, each archer eats 2 crop per hour, each cat eats 10 crop per hour. So as you build a bigger army you get a more negative crop production, to reduce the negative amount, occupy crop oasises, upgrade crop output levels, enhance your crops, spread your troops out in your sub cities, and/or upgrade the planting tech.