The distribution of soil phosphorus for global biogeochemical modeling

Abstract

Phosphorus (P) is a major element required for biological activity in terrestrial ecosystems. Although the total P content in most soils can be large, only a small fraction is available or in an organic form for biological utilization because it is bound either in incompletely weathered mineral particles, adsorbed on mineral surfaces, or, over the time of soil formation, made unavailable by secondary mineral formation (occluded). In order to adequately represent phosphorus availability in global biogeochemistry–climate models, a representation of the amount and form of P in soils globally is required. We develop an approach that builds on existing knowledge of soil P processes and databases of parent material and soil P measurements to provide spatially explicit estimates of different forms of naturally occurring soil P on the global scale. We assembled data on the various forms of phosphorus in soils globally, chronosequence information, and several global spatial databases to develop a map of total soil P and the distribution among mineral bound, labile, organic, occluded, and secondary P forms in soils globally. The amount of P, to 50cm soil depth, in soil labile, organic, occluded, and secondary pools is 3.6 ± 3, 8.6 ± 6, 12.2 ± 8, and 3.2 ± 2 Pg P (Petagrams of P, 1 Pg = 1 × 10¹⁵g) respectively. The amount in soil mineral particles to the same depth is estimated at 13.0 ± 8 Pg P for a global soil total of 40.6 ± 18 Pg P. The large uncertainty in our estimates reflects our limited understanding of the processes controlling soil P transformations during pedogenesis and a deficiency in the number of soil P measurements. In spite of the large uncertainty, the estimated global spatial variation and distribution of different soil P forms presented in this study will be useful for global biogeochemistry models that include P as a limiting element in biological production by providing initial estimates of the available soil P for plant uptake and microbial utilization

Modelling spatially explicit impacts from phosphorus emissions in agriculture

“…) and was derived from the P area density (Yang et al 2013) disregarding occluded P as it was assumed to be biologically unavailable. The area density was multiplied with the bulk density of the soil obtained from the HWSD (Nachtergaele et al 2012) and a depth of 0.5 m (Yang et al 2013).…”

“…The area density was multiplied with the bulk density of the soil obtained from the HWSD (Nachtergaele et al 2012) and a depth of 0.5 m (Yang et al 2013). Gaps in P area density and soil bulk density were initially filled applying focal statistics with a moving window of 11x11 cells and remaining gaps were set to the global mean.…”

“…Regarding initial P concentration in soil, two cases were considered: i) the total P concentration including potentially biologically unavailable occluded P is used and ii) only the sum of organic and labile inorganic P as P from secondary minerals or apatite becomes biologically available at a much slower rate (Smits et al 2012;Yang et al 2013). …”

Influence of climate variability, fire and phosphorus limitation on the vegetation structure and dynamics in the Amazon-Cerrado border

“…This global data set is part of 178 a database containing six global maps of the different forms of P in the soil (Yang et al, 2013). The Ptotal 179 was estimated from lithologic maps, distribution of soil development stages, fraction of the remaining 180 source material for different stages of weathering using chronosequence studies (29 studies), and P 181 distribution in different forms for each soil type based on the analysis of Hedley fractionation (Yang and 182 Post, 2011), which are part of a worldwide collection of soil profile data.…”

“…The Ptotal 179 was estimated from lithologic maps, distribution of soil development stages, fraction of the remaining 180 source material for different stages of weathering using chronosequence studies (29 studies), and P 181 distribution in different forms for each soil type based on the analysis of Hedley fractionation (Yang and 182 Post, 2011), which are part of a worldwide collection of soil profile data. The uncertainties and limitations 183 associated with this database are restricted to the Hedley fractionation data used, which are 17% for low 184 weathered soils, 65% for intermediate soils and 68% for highly weathered soils (Yang et al, 2013). …”