it should be grain

 Hello Archon. Back in time, in Sparta's stone ages, the troops could get dismissed if we hadn't any grain available, so we needed to  do a lot of raids, and when we were on vacation, it was possible to find fewer troops remaining in our acropolis. Thank Zeus, it was changed and now no need to lose our troops because of no grain, so you don't need to worry if you haven't any grain. You can always do your raids for grain, or to upgrade your farms and your Demeter statue. Of course, you can always kill your units  as we have a lot of  ongoing tournaments.

Hello Archon. Katia gave you good advice, I can add myself here to check if your grain production bonus is activated and also the 50% less consumption item. Without those, I always fall on negative. Good luck and let us know if you solved the issue!