For the last 14 years I have been maintaining part of my neighbors land which surrounds us on three sides. He hasn't tried to mow around us so I decided to start doing that and now I maintain about 30 feet on each of the three sides of our property to just make it look nice. The neighbor never compains about what I have done. After a period, do I have the right to take over that land which I have maintained for 14 years?

No you don't unless you have an agreement or if there had been a standing barrier in place for the 14 years. If you have no contract indicating payment of services then it's a gift in the eyes of the law.

Adverse possession laws vary by state, but are often 15 - 20 years, and require open, hostile, and continuous use, etc - the wording is pretty similar across states. In Canada, it may be called adverse occupation in some provinces.

Somehow I don't think a title will be granted to you for mowing 30 feet around 3 sides. Generally the 'adverse possession' implies structures and passageways, or possibly storage. You can try... but what does the neighbor say?

If you put up a fence on the property, put a storage buidling on it, and use it for just yourself. You may,

Merely mowing it, nope, you have just did him a favor,

You would be better off, not mowing, calling code enforcement for it being too tall and making him mow.