Crazy, isn't it! Once again, it is a question of how terms are defined. Biomass production just about always increases in response to additions of N. Then, something else becomes limiting, just as J. Leibig described at the birth of ag chemistry in the mid-1800s. In the northeast US, we had continuous additions of N (and S) via acid rain for some decades. The problem was that the N and S oxides which was not taken up by the tree tended to mobilize the essential bases (Ca and Mg especially) out of the naturally base-poor and acidic soil. Physical chemistry being what it is, potentially toxic Al became more soluble to become the primary buffer ion to the acid sulfates. Not a good thing. I have a paper (Greg Lawrence as senior author) on my FS website for description of some recovery with reduced S additions due to necessary regulation of industry.
So out your way, the soils tend to be more alkaline, so the soil chemistry interactions will be different. I think that the N fertilization may help sheer fiber biomass production and low-grade commodity timber, but be not so much a good thing for high-quality timber. So in crop production, the actual crop needs to be identified!
