Large Area Sheilding on plants

I was thinking the other day why shields haven't been used on plants service. the problems is power and the 2 power generates capable of produce enough power to put up a shield round a city.

1 the anti matter systems seem only to be space base i'm wondering if there is some common sense probation against employing them in a plants sservices.

2 the ZPM, at least large ZPMs could cause side effects on the plant due to there gravitation wells and also might not work in the gravitational well of the plant.