Soil Organic Phosphorus Transformations during 200 Years of Paddy-Rice and Non-Paddy Management in the Yangtze River Delta, China.

The chemical composition of soil phosphorus (P) changes with ecosystem development during pedogenesis, which has implications for phosphorus availability to plant and microbial communities. However, there are no published studies investigating organic P transformation during paddy-rice soil development although the UN-FAO estimates that lowland and irrigated rice production covers an area of about 132 million hectares. The objective of this study was to evaluate how prolonged paddy management influences organic P transformation and migration in the whole soil profile. We used NaOH-EDTA extraction and solution ³¹P nuclear magnetic resonance (NMR) spectroscopy to examine changes in soil P composition along a 2000-year paddy and non-paddy cultivation chronosequence derived from tidal wetland sediments in the Yangtze River Delta, China. The concentrations of organic P in paddy soils increased initially during the first 100 years of pedogenesis and then declined as soils aged. However, organic P (mainly orthophosphate monoesters) in non-paddy soil increased slowly with 700 years of pedogenesis. The dense plough pan due to repeated puddling increasingly hindered the supply of the subsoil with organic P from the topsoil. Overall, the results strengthen our understanding of organic P transformations during pedogenesis and provide important insight for understanding of biologically-available organic P under paddy and non-paddy management during ecosystem development.