Global assessment of soil phosphorus retention potential
Limited availability of P in soils to crops may be due to deficiency and/or severe P retention. Earlier studies that drew on large soil profile databases have indicated that it is not (yet) feasible to present meaningful values for “plant-available” soil P, obtained according to comparable analytical methods, that may be linked to soil geographical databases derived from 1:5 million scale FAO Digital Soil Map of the World, such as the 5 x 5 arc-minute version of the ISRIC-WISE database. Therefore, an alternative solution for studying possible crop responses to fertilizer-P applied to soils, at a broad scale, was sought. The approach described in this report considers the inherent capacity of soils to retain phosphorus (P retention), in various forms. Main controlling factors of P retention processes, at the broad scale under consideration, are considered to be pH, soil mineralogy, and clay content. First, derived values for these properties were used to rate the inferred capacity for P retention of the component soil units of each map unit (or grid cell) using four classes (i.e., Low, Moderate, High, and Very High). Subsequently, the overall soil phosphorus retention potential was assessed for each mapping unit, taking into account the P-ratings and relative proportion of each component soil unit. Each P retention class has been assigned to a likely fertilizer P recovery fraction, derived from the literature, thereby permitting spatially more detailed, integrated model-based studies of environmental sustainability and agricultural production at the global and continental level (< 1:5 million). Nonetheless, uncertainties remain high; the present analysis provides an approximation of world soil phosphorus retention potential.
The class for P-retention potential for a given soil unit, respectively mapping unit, may be coupled to recovery rates for fertilizer P derived from the literature. In combination with auxiliary knowledge/databases on climate, input levels, P-fertilizer application history, and crop-specific soil requirements, this information can serve as input to crop production models. As such, results of this study should permit spatially more detailed, integrated model-based studies of environmental sustainability and agricultural production. Within the current project on “Resource scarcity and distribution in a changing world,” the initial focus will be on model applications for Africa, but applied tools are principally developed for global usage. Global modelers may also use the data for broad scale analyses.
Data format: Zipped (GRID, ArcMap9.x; tabular data in MSAccess (ver. 2002-2003), and Report )