Manufacturing

• The first step in the manufacture of phosphate fertilizer is creation of phosphoric acid. Manufacturers create phosphoric acid using one of two processes: a dry process or a wet process. With the dry process, workers heat rock phosphate in electric furnaces; with the wet process, workers treat rock phosphate with acidic chemicals. Regardless of the process they use, workers then heat the resulting phosphoric acid to release water, which produces a superphosphoric acid---a phosphoric acid that is about 75 percent phosphate. The phosphates in phosphate fertilizers can be both orthophosphates, which plants utilize directly, and polyphosphates, which break down into orthophosphates upon mixing with soil.
  
  

Phosphate Fertilizer Types

• Phosphate fertilizers are available in two primary formats: liquid and granular. With a liquid phosphate fertilizer, application requires attaching a bottle of the fertilizer to a garden hose and then spraying the resulting solution onto your garden's soils. Alternatively, you may mix the liquid fertilizer and some water into a watering can. With a granular phosphate fertilizer, application requires either spreading the fertilizer granules by hand or by using a device such as a seed/fertilizer broadcaster. Chemically, liquid and granular phosphate fertilizers are identical, and one does not tend to out-perform the other. The main difference is that plants absorb the phosphate in liquid fertilizer more rapidly, while they absorb the phosphate in granular fertilizer more slowly. So while liquid fertilizer may provide faster results, it also requires more frequent applications.
  
  

Pollution

• Over-applying and over-spreading phosphate fertilizers can have ecological consequences, especially when it comes to bodies of water. While phosphates bind well to soil particles, if these particles spill over into driveways, sidewalks and streets they can enter storm drains and eventually end up in rivers and lakes. Excess phosphates in such areas can cause water weeds and algae.
  
  

Clarification

• According to Washington State University, despite what some gardeners claim, phosphate fertilizers do not stimulate root growth in transplanted shrubs and trees. Instead, the best option for promoting root growth is a nitrogen-rich fertilizer. Supplying phosphate fertilizers to shrubs and trees following transplantation can cause leaf chlorosis, as excess phosphates in the soil will compete with manganese and iron. These elements are essential for plant chlorophyll production.