Phosphorus sorption capacities and saturation of soils in two regions with different livestock densities in northwest Germany

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Abstract
Soils in areas with high livestock density contribute to the eutrophication of aquatic ecosystems through loss of nutrients, especially phosphorus (P). In order to identify the potential for P loss from such soils we determined phosphorus extracted by water (H 2 O‐P), by double lactate (DL‐P), and P sorption capacity (PSC) and degree of P saturation (DPS) in soil samples from two counties, one with low (Harle‐catchment) and the other with very high livestock density (Vechta). Both catchments are hydrologically connected with the tidal areas of the North Sea. The mean concentrations of H 2 O‐P (0.4mmol/kg) and DL‐P (3.9 mmol/kg) were lower in the Harle‐catchment than in the Vechta area (1.2 mmol/kg, 6.8mmol/kg). Although oxalate‐extractable Al (Al ox ) and Fe (Fe ox ) and the derived PSCs varied according to soil type and to land use, the livestock density and the resulting high concentrations of oxalate‐extractable P (P ox ) were shown to be the main reason for the very high DPS of up to 179% in the county of Vechta. These values exceeded DPS reported from other intensive pig feeding areas in western Europe and indicate the potential for significant P loss. Less than 40% of the variation in P ox could be explained by the routinely determined H 2 O‐Por DL‐P. Geostatistical analyses indicated that the spatial variability of P ox depended on manurial history of fields and Al ox , showed still smaller‐scale variability. These were the major constraints for regional assessments of P losses and eutrophication risk from agricultural soils using available soil P‐test values, digital maps and geostatistical methods.

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