Rapid changes in phosphorus species in soils developed on reclaimed tidal flat sediments

Abstract

Phosphorus (P) plays a key role in the global biogeochemical cycle. The dynamics of P in soils is of considerable importance to the management of soil fertility. However, little is known about P dynamics in reclaimed land at the centennial scale during the initial stage of soil development, when the ambient conditions undergo substantial changes. In this study, conducted in Eastern China, we used a sequential extraction method to analyze the changes in P species in sediments and soils in a coastal reclaimed area representing a sequence of soil ages. Significant accumulation of total P accompanied by organic matter enrichment, desalination, and decalcification were observed in the initial pedogenesis of reclaimed tidal flat sediments. A rapid change in top soil P species within a century of pedogenesis was revealed, which was characterized by a marked decline in P contained within primary minerals (DeP) and an increase in loosely absorbed P, Fe-bound P, authigenic P (CaP), and organic P. DeP decreased from 67.3% to 25.3% of total P, whereas CaP increased from 8.4% to 32.9% along the reclamation gradient. Dissolution of primary minerals and a high rate of fertilization were identified as the major causes of this P trajectory. A key factor controlling the evolution of soil P speciation is the marked change in ambient conditions following land conversion, resulting in a shift in anaerobic conditions, a decrease in pH, accumulation of organic matter, and depletion of carbonates. Under the strong interference of human activities, the P dynamics in soils derived from tidal flat sediments differ from those predicted by the Walker and Syers model. Our results indicate that current nutrient management practices in the studied area can not only avert soil P depletion but also increase P availability.