Competitive sorption and accumulation of organic phosphorus in phosphate-rich soils and sediments

Phosphorus (P) loss from intensively managed agricultural soils is a well-known environmental issue in the world because of its negative impact on aquatic environments (e.g., eutrophication and hypoxia). Most soil P chemistry research focused on the accumulation of phosphate or total P(TP) in soils and sediments. However, coaccumulation of an organic P(Po) fraction has not been extensively investigated. Our review showed that Po fraction could be as high as ~ 80% of TP in some soils and sediments. Furthermore, Po species could competitively sorb in soil adsorbents to keep phosphate in pore water or be mineralized. Mineralizable Po fraction in soils and sediments is as important as orthophosphate when bioavailability of phosphate is of concern to soil fertility and the degradation of water quality. This review addresses the degree of Po accumulation in P-rich soils with the history of fertilizer application, inherent soil properties and environmental factors affecting the competitive sorption of Po. In soils and sediments, orthophosphate is one of the predominant forms of inorganic P(Pi), whereas phytic acid is the most common Po species. Many Po species contain one or more phosphate functional groups and readily react with variable charge mineral surfaces as phosphate does. Past research showed that phytic acid competitively sorbs in soils with phosphate. Reaction conditions, such as a ratio of phosphate/phytic acid and reaction times affect the adsorbed species at the soil mineral-water interface and in soils. Knowledge gaps and future research needs to improve the current state of legacy P are also discussed.