For a while I've been thinking about why so few organisms are able to effectively utilize nitrogen from the air. But, if all plants could derive all the Nitrogen they needed from the air, it could throw a number of systems into an imbalance. As the article indicates, ocean systems could be thrown into chaos, and likely both N2 and CO2 levels would fall dramatically (in the absence of humans)... leading to a crisis. I guess I am always amazed at the natural balance of things, which, of course, humans tend to ignore.
I do use a little fertilizer in my vegetable garden. Stuff just grows better with it. But, I also have no surface runoff, at least during the summer. Whether or not subsurface penetration of Nitrates is a problem is another question. I know Geezer said that he regularly tests his well water for it.
But, we would do well by developing agriculture with minimal added fertilizer and water. I know that a significant amount of wheat is grown in Washington with no added water, and just the moisture that naturally falls into the desert-like area.
The problems, of course, are multi-fold. Individual farmers wishing to maximize their output, and thus profits, and the extraordinary global requirements for food. I presume much of the runoff occurs with canal irrigation which is relatively cheap and effective. Other types of irrigation such as drip irrigation tend to have much higher equipment costs and are higher to maintain.
Perhaps we could breed plants that would flourish with minimum fertilizer. And, then also better utilize cover crops, and naturally nitrogen fixing crops that might release less free nitrogen into the streams.