Yes, exploitable land can be owned by an individual in a socialist economy. If you’re growing food for your family, then that’s just one family the state doesn’t have to feed. If you’re growing food for your community, then that’s several mouths the state doesn’t have to feed. If you’re hoarding or selling food (or in one very famous historical case, burning it out of spite), then you are monopolizing a resource that could be feeding people, and the state will intervene, whether by buying your land back from you, taking it from you, liquidating you as a class, or some other solution to be determined by the state in question - there is no one size fits all blueprint to socialism.