Most commercial P fertilizers now on the market are made by treat- ing phosphate rock with certain acids or, to a smaller degree, with heat. The result has been products with improved agronomic and physi- cal properties. The rest of the publication deals with these materials. Phosphoric Acid Phosphoric acid is produced by two methods. Furnace acid is costly to produce and is used primarily for food and other industrial processes since it contains very few impur- ities.
Phosphoric acid is a good P source for plants.
However, because of handling and application problems, it is normally processed into other P fertilizers. NSP is used as a direct-application material and as an ingredient in some mixed fertilizers. The resulting product is mainly MCP, with very little sulfur present since sulfuric acid is not directly used in the production process. Because of its higher analysis, which results in reduced shipping and handling costs, TSP is favored over NSP when sulfur is not needed. Three of the common ammonium phosphates are monoammonium phosphate, diammonium phosphate, and ammonium polyphosphate.