Vegetated Buffer Strips Under Pressure: Phosphorus Dynamics in Soils with and Without Fertilizer History

Abstract Purpose: Vegetated buffer strips (VBS) are key landscape elements for retaining phosphorus (P) and reducing its transfer from agricultural land to surface waters. While long-term P retention in VBS is well documented, short- to medium-term transformations among specific P pools during drying-rewetting events remain poorly understood. It therefore remains unclear whether VBS function as temporary sinks or sources of P under continued fertilizer inputs. Methods: We investigated P dynamics in P-saturated VBS soils and undisturbed forest soils (FST) under contrasting hydrological regimes. Following the addition of dissolved inorganic P (P i ), soils were incubated for 16 weeks under short-pulsed (SPL, weekly) and long-pulsed (LPL, biweekly) drying-rewetting cycles at 20°C and 5°C. Sequential P extractions were used to track P i and organic P (P o ) pools from labile to more stable fractions. Results: In VBS soils, surface-bound P i (NaHCO₃-extractable) dominated throughout the incubation, with limited transfer into more stable pools. Stable P i and P o (CDB-extractable) increased under SPL but were reduced under LPL conditions. In contrast, FST soils showed strong accumulation of P i in stable NaOH- and CDB-extractable pools, indicating a higher P retention capacity. Conclusions: Overall, the results demonstrate that VBS soils with legacy P saturation are vulnerable to P remobilization under fluctuating hydrological conditions, highlighting the importance of accounting for hydrological variability and land-use history when evaluating VBS effectiveness.