Abstract
A survey of the interactions between phosphorus (P) species and the components of calcareous soils shows that both surface reactions and precipitation take place, especially in the presence of calcite and limestone. The principal products of these reactions are dicalcium phosphate and octacalcium phosphate, which may interconvert after formation. The role of calcium carbonate in P retention by calcareous soils is, however, significant only at relatively high P concentrations – non-carbonate clays play a more important part at lower concentrations. In the presence of iron oxide particles, occlusion of P frequently occurs in these bodies, especially with forms of the element that are pedogenic in origin. Progressive mineralization and immobilization, often biological in nature, are generally observed when P is added as a fertilizer.Manure serves both as a source of subsurface P and an effective mobilizing agent. Blockage of P sorption sites by organic acids, as well as complexation of exchangeable Al and Fe in the soil, are potential causes of this mobilization. Swine and chicken manure are especially rich P sources, largely due the practice of adding the element to the feed of nonruminants. Humic materials, both native and added, appear to increase recovery of Olsen P. In the presence of metal cations, strong complexes between inorganic P and humates are formed. The influence of humic soil amendments on P mobility warrants further investigation.
Highlights
The mobility of phosphorus (P) in the shallow subsurface is a matter of critical importance and considerable complexity
The shortterm availability of P to crops is strongly influenced by biochemical processes that affect organic matter, while its long-term status is generally determined by geochemical transformations
Concluding remarks Much has been learned about P mobility in calcareous media over the last five decades, but some gaps in understanding remain
Summary
The mobility of phosphorus (P) in the shallow subsurface is a matter of critical importance and considerable complexity. High application rates of manure lead to P mobilization, indicating that organic materials with high P content may substitute for CaCO3 as a soil amendment to decrease the P sorption capacity and increase the pH [60,65]. Turner and Leytem caution that the presence of organic P in the HCl extract of the Hedley fractionation [79] procedure is commonly overlooked, resulting in under-reporting [80] They found phytic acid to be present in HCl extracts of broiler litter and swine manure, indicating that this relatively immobile compound enters the environment from these sources. The practice is gaining popularity – as borne out by the existence of more than 70 purveyors of these "nonconventional soil additives" in the U.S alone [53] – but nothing is known about its environmental consequences
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