Hi, does anyone know what the rusty pipe sticking out of the ground under my v mature apple tree might be?

At the back of my mind, I suspect that it may be a way to deliver moisture/nutrients straight to the tree's roots. On the other hand it may just be an old post for holding a washing line (but then why would it be under a tree)

Does anyone have any thoughts?

Thanks to anyone who takes the time to reply and sorry if the answer is obvious - I'm a bit of a noob to this gardening business