Determining Plant Available Phosphorus of Enhanced Efficiency Fertilizers Using Phosphorus Adsorption Isotherms.

Producers in arid regions applying high amounts of P fertilizer because of high Ca-P fixation rates. The high levels of free lime or calcium carbonate (CaCO₃) in arid soils reacts with phosphorus (P) to precipitate out Ca-P minerals that are not available to plants (P fixation). The high amounts of P applied to arid soils increases the risk of P runoff and loading of surface waters that causes eutrophication and negative environmental impacts. Researchers and industry are constantly developing new P enhanced efficiency technologies that will decrease the amount of P loss through P fixation thereby increasing P fertilizer efficiency for reducing environmental impacts and improving crop growth and yield. Some of these technologies include, organic substances (Humic Acid), ortho-poly phosphate fertilizers, and long, highly charged cationic polymers (e.g., maleate copolymer or Avail) have been used to decrease P fixation and increase P fertilizer efficiency. Determining the rate that P fixation that will occur can reduce if not eliminate the over application of P by producers and furthermore reduce runoff into watersheds. The objective of this study was to determine P fixations from several enhanced efficiency P fertilizer on calcareous soils over a 1d, 3d and 7d time period and to use that data to adjust P fertilizer recommendations for enhanced efficiency fertilizers.