As said by the previous poster, we need more detail to analyze the problem. However, the problem will certainly be some inefficiency; DF makes it easy to get food on any map with sand or soil or grass.
If you are having trouble growing enough food, then one or more of the following is likely at issue:
* You might lack any sort of soil or sand (this is rare), or have placed your farm in some inconvenient spot. You may have failed to bring enough seeds. The solutions in these cases include trade, hunting, fishing, and gathering.
* You might either have no-one assigned to farm, or the dwarves that are allowed to farm may have been told to also do other things (like hauling) that keep them away from the fields.
* You may be making your dwarves walk too far. Watch your dwarves and notice how much time they waste just walking about instead of actually doing the job you assigned them. Dwarves are short-legged little guys who hate long hikes.
Put the seeds near the fields. Put the fields near the harvest stockpile(s). Put them near the workshops that use plants. Put these near the edibles stockpile. Put that near the dining hall. Put the liquor stockpile near where most dwarves are most of the time. Use vertical connections - they let you combine lots of work space and short walks. Use these methods for all your industries.
* You may lack enough stockpile space for harvested crops, or enough space to store edibles and booze. You may not have a still to make booze or a kitchen to make prepared meals. You may have neglected to make enough barrels to store stuff, or enough bags to hold your seeds and certain kinds of prepared goods.
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Farming in DF is extremely productive; I personally think it is /too/ productive. Once you optimize your farming and food-processing, it is quite possible for two or three sufficiently skilled dwarves (one farmer-cook; one or two farm-brewers) to grow, harvest, cook, and distill enough food and liquor for eighty.