Accumulation of phosphorus (P) in agricultural topsoils can contribute to leaching of P which may cause eutrophication of surface waters. An understanding of P mobilization processes in the plough layer is needed to improve agricultural management strategies. We compare leaching of total dissolved and particulate P through the plough layer of a typical Danish sandy loam soil subjected to three different P fertilizer regimes in a long-term field experiment established in 1975. The leaching experiment used intact soil columns (20 cm diameter, 20 cm high) during unsaturated conditions. The three soils had small to moderate labile P contents, expressed by water-extractable P (3.6–10.7 mg/kg), Olsen P (11–28 mg/kg) and degree of P saturation (DPS) (25–34%). Mobilization of total dissolved P (TDP) increased significantly (P < 0.05) from the intact soil columns with increasing labile P, whereas the increase in particulate P (PP) with increasing labile P content was modest and statistically insignificant. We found concentrations up to 1.5 mg TP/L for the plough layer of this typical Danish sandy loam soil. This highlights that even a moderate labile P content can be a potential source of TDP from the plough layer, and that a lower concentration margin of optimum agronomic P levels should be considered. Keywords: Dissolved phosphorus, particulate phosphorus, leaching, mobilization, labile phosphorus, soil phosphorus status, Olsen phosphorus, water-extractable phosphorus, oxalate-extractable phosphorus, iron and aluminium Abbreviations: DPS, degree of P saturation; PP, particulate P; PV, pore volumes; TDP, total dissolved P.
Soil Use and Management, 2013, Vol 29, Issue 3, p. 297-305
Dissolved phosphorus; particulate phosphorus; leaching; mobilization; labile phosphorus; soil phosphorus status; Olsen phosphorus; water-extractable phosphorus; oxalate-extractable phosphorus; iron and aluminium