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Phosphate fertilizer

​Learn more about the role of phosphate in crop nutrition, how much is needed and when, and what happens to it in the soil.

Manufacturing phosphate fertilizer

Phosphate fertilizer is manufactured from rock phosphate. Rock phosphate is mined and processed into phosphate fertilizer primarily in the United States, North Africa, and the former Soviet Union. Historically, rock phosphate was used as a fertilizer, but because of low concentration and low availability, most applied fertilizer has been processed into a higher concentration.

 

Types and concentrations

There are several types of fertilizer available on the market, in both liquid and dry granular form.
 
The choice of liquid or dry formulation should be based on the fit for individual farming operations. The effects of environmental conditions, soil properties, and method of application are the same for liquid and dry formulations. The fertilizer choice should be based on cost, availability, and fertilizer placement options.
 
Similarly, soil pH should not influence the choice in phosphate fertilizer formulations. Agronomic studies have not found differences between MAP and DAP, so formulation selection should be based on other factors.

P fertilizer type Analysis     Properties
Rock phosphate 0-(3 to 8)-0 Raw mined product with limited phosphate availability
Superphosphate (OSP or SSP) 0-20-0-10S Results from reaction of rock P with sulfuric acid - an older form of phosphate
Triple Super Phosphate (monocalcium phosphate) 0-45-0 Solid granular fertilizer with good handling properties
Monoammonium phosphate (MAP)
11-48-0
11-51-0
11-52-0
11-54-0
11-55-0
A solid granular that does not absorb moisture during storage. It is fairly resistant to breakdown during handling
Diammonium phosphate (DAP) 18-46-0 Solid granular fertilizer with higher level of nitrogen
Ammonium Polyphosphate 10-34-0 The solution will settle out below -18 °C and must be brought back into solution
 
Many dry blends of urea and ammonium phosphate are also available, with analysis such as 28-28-0, 17-34-0, etc.


Poloyphosphate vs. orthophosphate


During fertilizer production, rock phosphate reacts with an acid to produce phosphoric acid. Two types of phosphorous compounds are present. Polyphosphates are a series of orthophosphates that are chemically joined together. Polyphosphate is basically two or more orthophosphates ions combined together when water is removed.
Some phosphate fertilizer contain orthophosphates only, while others have both poly- and orthophosphates. However, upon contact with the soil, polyphosphates will absorb water and readily convert back to orthophosphate. This conversion can be completed in days with normal soil temperatures, so crop response to phosphate fertilizer is the same, no matter what the formulation base.
 
The effect of orthophosphate and polyphosphate fertilizers on crop production was evaluated at the University of Minnesota at 15, 30, and 45 lb/ac of applied P2O5. Resulting yields at the three levels of applied fertilizer were the same for both poly- and orthophosphate. Note: 11-52-0 is 100% orthophosphate, most liquid fertilizers are polyphosphates.

The influence of P source on corn yield

P2O5 P Source
Applied Polyphosphate Orthophosphate
lb/acre bu/acre
15 124 124
30 134 134
45 142 142
Source: G. Rehm et. al; Understanding phosphorus fertilizers; University of Minnesota. 2002

 

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