One of the early problems that many players have is resource management - particularly that of crop production. Many buildings, fields, and troops place a constant drain on crop production as designated by the 
icon in production.
For example, a level 1 woodcutter requires: 
40 
100 
50 
60 
2, which means it consumes 2 crop per hour. This crop consumption is cumulative.
Across the top of the screen, you can see your current resource stores and free crop:
To increase crop production, you can upgrade a crop field, mill or bakery. Assuming you have the requirements, you will be able to do so, noting that level 1 cropland requires 20 crop itself for construction.
Negative crop production and its effects
When you have to feed more troops and population than your production, the crop production value becomes negative, this indicates that the troops in the village will empty the granary. If you do not refill it before the stored crop reaches 0, the troops will slowly start to die of starvation. Once crop production reaches 0, starvation will stop.
Clicking the crop balance icon (the last on the right in the image above) will show you the details of crop production and usage for the active village.
Free crop
Free crop is the crop production minus the population.
- Includes Oasis, Mill and Bakery bonuses
- Does not include hero bonus or plus crop bonus
In general, a construction/upgrade that would cause free crop to go below 1 is not permitted. There are some exceptions to this rule, that make it possible to upgrade crop production even in such a situation.
Limitations and Exclusions
- You can always upgrade a crop field.
- Grain mill and bakery may be built/upgraded if they would increase free crop.
- Main Building level 1 may always be built.
- If base crop production in the village is 276 per hour or more, then Main Building, Warehouse and Granary may be built/upgraded to level 10 regardless of free crop.
- World Wonders are excluded and may always be upgraded.
- You cannot destroy grain mill nor bakery if it would drop free crop below 1 (Any running destruction of these is already counted).
Hero crop production
The hero has a basic crop production of 6 crop per hour, no matter how the skill points are set. This basic production follows the same rules as the usual hero resource production. So it's added to the production of the village that the hero belongs to. But it does not increase the free crop.
- A dead hero still produces 6 crop per hour.
- When a hero is revived, then his resource production starts at the same time as his crop consumption.