That statement isn't exact, because whether it's stubble or summerfallow seeding, a starter blend is usually added with the seed (i.e. 11-55-00 ammonium phosphate) plus traces, but the bulk of additional nitrogen fertilizer can be eliminated on fallow land.

In a dark brown/black soil zone in Canada, like where our farm is and a lot of Canola is grown, generally you can grow an equivalent crop of cereal or oilseed on land that was fallowed the previous year compared to continuous cropping with 60-100+ lbs/acre of urea.

Legumes (i.e. soybeans) also don't require additional nitrogen fertilizer. An option to summerfallow in Canada is to rotate a legume like alfalfa.

Corn and feed wheat in continuous cropping low-till methods would be about the highest nitrogen requirement crops.

My dad would fallow about 1/3, but it is rarely done now for several reasons (diesel price, wind erosion, bank taking the farm if every acres isn't seeded, etc). One of the major issues with Canola is disease and although fallow acres are much less than ever, I would think if there is any fallow, more often than not Canola seeded in the next rotation.

If winter rains arrive Down Under I'm going to plant a small field of 'Tornado' variety canola on soil prepared with charcoal and small amounts of NPK (urea, phosphate, potash) and dolomite. Wide row spacing should help with bug control using a backpack spray.

However I'm swinging to the view we should use oily weeds for biodiesel, not food crops. Better still go the gasification route which unfortunately is in another league financially.