Araucaria araucana root:deep roots These are the pertinent facts about your tree. From them we can see that anly waterlogging is going to cause problems. Because the roots want to go deep, there may be a problem if they are encountering clay or bedrock.  If you lime the area, that would throw the pH off.
I know of no disease that bothers these trees in our area, but a multitude of problems may occur because of culture and environment. For example, this is a tree that prefers low fertilizer and no weed killers. The good drainage is the overriding factor.
If you know the pattern of yellowing, that would help. If it is only the oldest growth, that may even be normal. These trees sluff off old branches.
I hope this has been of some help.
PS the fact that it is in the midst of a lawn raises warning signals about pH and weedkillers, particularly Roundup. It appears that the newest growth is most affected.