Welcome to the debate of the year.
From what I have heard, there is some sharing going on between still-living nitrogen-fixing plants and other plants that need nitrogen.
I have also heard that Fukuoka "stressed" his clover by cutting it back. The clover drops it's root nodules, there's a general boost of free nitrogen in the area, and other plants gobble that up. The clover grows back and can be stressed again later on.
best,
William