rock phosphate shortage, page-4

PROM = phosphate rich organic manures

Instead of adding sulfuric acid to make the phosphate soluable the job is done by organic acids in the manure.

Been used by biodynamic farmers for a long time. I believe it requires very well managed compost to acheive satisfactory results.

Seems there is research being done to make it more widely useful.

see this link

http://precedings.nature.com/documents/2411/version/1

"Certain types of rock phosphates of sedimentary origin are applied to acidic soils as fertilizer directly. Recent research in India showed that high grade rock phosphate in fine size when used as a mix with organic manure works as efficiently as di-ammonium phosphate (DAP) in alkaline soils"

Key point is ...
it still requires rock phosphate