Kentucky bluegrass and centipede usually can't grow in the same soil. Can you post a picture?

Also, where do you live? Are you on the delta or what/where?
How have you been caring for the centipede? How often do you water, mow, and fertilize?
Are you sure it's centipede and not St Augustine?
Is shade a factor in your lawn?

Attached are some pics of the weed. Sounds like I was mistaken and its not really bluegrass. Some people are saying its either sedge or possible "hurricane grass"? I'm not really sure how to handle either, but I need to make sure I kill it and try to ensure it does not come back in the future! Let me know what you think I can do to stop it from taking my centipede lawn.

Closeup of roots

Another close up.
In regards to maintenance (live just outside New Orleans, LA), I need to cut back on the water. I set my irrigation to run at 5am for about 15 mins every other day but I am starting to do about 25 mins twice a week. I normally mow once a week and try to keep it cleanly cut. I had a friend come out who is a golf superintendant check out my grass a few months ago and used a device that he had. I know its not the best way to measure soil, but he literally said there was almost no nitrogen. I put down a 1/2 application of 32-0-10 about 2 weeks ago to see if that would help. Any advice on what I should do? I know you're the guru around here so I appreciate any advice.