Yesterday I read something about phosphorus supplies (as it applies to matches and fertilizer):

But the real lesson here is not the danger of over-reliance on Chinese imports. It’s the disparity between the international and Chinese domestic prices for fertilizer chemicals. As with energy, the Chinese government keeps the price of fertilizer low domestically to keep costs down for farmers. Which means that phosphorous mining and chemical companies can make much more money by exporting their products than by selling them locally. Thus the export duty, designed to close that window.

Today I read about nitrogen:

Tom Philpott is right to highlight the tremendous ecological debt we’ve built up by depending on nitrogen fertilizer to run our crop production system. Depending on mined and fossil-fuel produced nitrogen for our food is no more sustainable than depending on peaking oil and mountain-top removed coal for our energy.