Natural pre-human phosphorus cycle

GLOBAL PHOSPHORUS CYCLING Natural (pre-human) phosphorus cycle 

Apatite minerals, the dominate weathering source of P, vary widely in chemistry and 

Apatite dissolution phosphate rock and synthetic hydroxyapatite (HAP). The 

Several workers have attempted to develop dissolution rate equations to model apatite dissolution (Olsen 1975, Smith et al. 1977, Christoffersen et al. 1978, Fox et al. 1978, Chien et al. 1980, Onken and Metheson 1982, Hull and Lerman 1985, Hull and Hull 1987, Chin and Nancollas 1991). Rate equations from these models include zero order, first order, parabolic diffusion, mixed order, and other forms. The most current model (Hull and Hull 1987) focuses on surface dissolution geometry, which the authors argue fit the experimental results better than previous dissolution models. These experiments and the dissolution rate equations derived from them are missing the experimental conditions that replicate the natural dissolution processes and agents in soils, as they do not include the range of apatite mineralogies likely to be naturally weathering in soils. 

Phosphorus cycling in soils. The cycling of P in soils (see Fig. 1) has received much attention, both in terms of fertilization and the natural development of ecosystems. Of the approximately 122,600 Tg P within the soil/biota system on the continents, nearly 98% is held in soils in a variety of forms. The exchange of P between biota and soils is relatively rapid, with an average residence time of 13 years, whereas the average residence time of 

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