In essence, it's essential for agriculture, and wasteful usage and limited supplies are pushing prices up dramatically. In a few decades, we may be looking at 'peak phosphorus'.
One of the possible solutions involves recycling the phosphorus that we throw away every day - urine.
I recently read Liquid Gold, an entertaining (It's full of anecdotes on how urine has been used throughout history) and informative book on how to use urine in your garden. Urine is sterile (as long as it isn't contaminated by faeces) and contains nitrogen, phosphorus and potassium in almost the exact ratio needed by plants. Dilute between three and eight times with water (the more woody material/mulch/compost you have in the soil, the stronger you can make the mixture) and you can feed your plants up to three times a week.
I tried this a couple of weeks ago on my courgette plants - the leaves were turning yellow and the plants were putting on very little growth.
Result? Green leaves within a week and healthy new growth.
Tried again with the sorry-looking French beans - they're now, finally, making decent growth up their poles.
I'm now encouraging the family to fill empty plastic milk bottles as fast as they can - there's a load more plants that I want to try this on!
It's supposed to be particularly good for spinach.