Why is 田 read as だ instead of た/でん in 山田?


When looking up 田 on
[Jisho.org/田](http://jisho.org/search/%E7%94%B0%20%23kanji), it states it's
readings as た and でん, but when the kanji is used in the family name Yamada
(山田), the reading obviously changes to 'da'/だ.

Is this something you just 'have to know'? Or why isn't the fellow called
Yamata?

