Bridgford, Roy O.Rost, C. O.2012-10-232012-10-231958https://hdl.handle.net/11299/13702815 pagesWHAT IS THE MOST efficient phosphorus fertilizer? The question is not as simply answered as it could have been 8 few years ago. Modern technology has produced many different fertilizers containing phosphorus, but superphosphate is still the backbone of the fertilizer industry. All fertilizer phosphorus comes from phosphate rock-tricalcium phosphate. The phosphorus in the rock is not readily available to crop plants because the natural rock contains 1 to 3 percent of fluorine, and this makes the phosphorus soluble with difficulty. Nevertheless, it has been and still is the practice to grind the rock very finely and use it for fertilizer, since some of the phosphorus becomes available with time. In the fertilizer trade, this finely ground rock is called by various names such as "rock phosphate," "ground rock phosphate," and "raw rock phosphate."en-US