The salary/celery merger is an example of neutralization. Two vowels that are clearly distinguished in words such as land and lend are pronounced with the same vowel. It is the vowel of land.
Dialects of English which are known to have the feature are the Australian (the state of Victoria), New Zealand and Norfolk in England. All the dialects with the salary/celery merger have a velarized lateral. In those dialects that have the merger, the front mid unrounded lax vowel of celery is lowered to the low vowel of salary.
The position of the tongue for the lateral influences the pronunciation of the preceding vowel. In Australia, the merger has been observed in Melbourne, the largest city in the state of Victoria. However, the merger is resisted in dialects that do not have a velarized lateral.