Lai, Ying-RenYing-RenLaiWang, Shan-LiShan-LiWang2025-11-272025-11-272025-06-05https://www.scopus.com/record/display.uri?eid=2-s2.0-105009004754&origin=resultslisthttps://scholars.lib.ntu.edu.tw/handle/123456789/734224Biochar is considered a promising amendment for improving phosphorus (P) availability in agricultural soils; however, its effects on the chemical transformation and long-term immobilization of P in submerged soils across soil depth and over time remain unclear. This study conducted a 98-day column incubation experiment to investigate the effects of rice straw biochar (RSB) on the spatial and temporal dynamics of iron (Fe) and P under soil submergence. Soils with and without biochar addition were mixed with water homogeneously and then added into each PVC column with an additional standing water layer above the soil surface. The results revealed a two-stage shift in soil redox potential (Eh), with more rapid changes observed at deeper depths. RSB addition accelerated the decline in Eh and increased the soil pH. The rise in pH by submergence and biochar addition promoted the release of soluble and exchangeable P from soil to pore water during incubation. Ca-associated P precipitation and re-adsorption resulted in relatively low phosphate concentrations in pore water. RSB addition increased P availability in the early stage by releasing soluble and exchangeable P and promoting phosphate desorption through pH elevation, which increased the negative surface charge of soil constituents, thereby reducing their affinity for phosphate and enhancing its release into the pore water. However, prolonged submergence led to the transformation of soluble and exchangeable P into more stable Ca-P precipitates, limiting long-term P availability. These findings provide new insights into the temporal and spatial dynamics of P in submerged soils and highlight the short-term benefits and long-term limitations of biochar for sustaining P availability in paddy rice systems.truebiocharchemical transformationiron cyclephosphorus cyclesoil phosphorus fractionationsoil redox potentialsubmerged soiltemporal dynamics[SDGs]SDG2[SDGs]SDG6[SDGs]SDG12[SDGs]SDG13[SDGs]SDG15journal article10.3390/agronomy150613942-s2.0-105009004754