As far as I can tell, the word is only used in Sri Lanka and is not common to other varieties of English. There is no entry in the Oxford English Dictionary.
However, English is a constantly evolving language and words are frequently assimilated from other languages when needed. If you wish to use it, then I would recommend giving a definition upon its first use, to help the unfamiliar reader. As a matter of style, I would always try to use the simplest word that conveys the meaning I wish; therefore, I would not use "aswaddumization" unless it has particular connotations that are not conveyed by by "cultivating the land". Perhaps, it refers specifically to the conversion of fallow land to a particular type of paddy field?