When we bought our first house, we inherited a mature Meyer lemon tree which fruited constantly with absolutely no care whatsoever.

So when we moved, I planted one. Eight years later, despite full sun, watering, fertilizing, and picking off the snails, well, it just doesn't seem happy.

It has grown quite tall, and blooms profusely, but fruits very infrequently. A lot of the leaves are yellow, mostly the new ones. When it does fruit, the fruit gets enormous and takes forever to mature.

Obviously there's a very severe nutrition problem here, but I don't know how to go about diagnosing it or correcting it. Nearby plants don't seem to be quite so upset. Please help!