First of all you must read the beginners guides they will help you enormously in playing well the game.

Your troops eat food and therefore that is deducted from your produced thus giving you then a surplus or a lack of the food resources. More troops more comsumption of food. THis is displayed in negative terms. If you Have more troops than food produced you have a negative production displayed.

Read the ULTIMATE GUIDE several times and many others.

Take care Drakko