Resumen
Extended waterlogging (WL) conditions in heavily manured soils can change soil phosphorus (P) dynamics. We assessed the effects of soil moisture regimes (field capacity (FC) and WL) and P rates on (i) dry matter (DM) yield and P offtake of ryegrass, (ii) changes in soil Fe3+, Fe2+, and soil P, and (iii) risk of P leaching. The treatments were tested in a four-month greenhouse experiment using intact soil columns and annual ryegrass (Lolium multiflorum). The DM yield and P offtake were lower under WL compared with FC. The concentration of Fe3+ was 1984 mg kg-1 (0?30 cm) under FC, but 1213 mg kg-1 at 0?5 cm and 2024 mg kg-1 at 25?30 cm depth under WL. The concentration of Fe2+ was 244 mg kg-1 (0?30 cm) under FC, but 2897 at 0?5 cm and 687 mg kg-1 at 25?30 cm under WL. The water extractable P (Pw) was 12.7 mg kg-1 at 0?5 cm and 9.5 mg kg-1 at 25?30 cm under FC, but 8.6 mg kg-1 at 0?5 cm and 10.5 mg kg-1 at 25?30 cm under WL. The P saturation index (PSI) was 27.2% at 0?5 cm and 17.4% at 25?30 cm under FC, but averaged 11.9% at 0?30 cm under WL. We can conclude that extended WL associated with flooding creates reducing conditions in the soil, thus decreasing the concentration of Fe3+, but increasing the concentrations of Fe2+ and the solubility of P which can exacerbate the risk of P loss with runoff and leaching.