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Open AccessArticle

Sources and Pathways of Formation of Recalcitrant and Residual Phosphorus in an Agricultural Soil

Department of Plant and Soil Sciences, University of Delaware, Newark, DE 19716, USA
Key Lab for Surficial Geochemistry (MOE), School of Earth Science and Engineering, Nanjing University, Nanjing 210023, China
Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory, Richland, WA 99354, USA
Author to whom correspondence should be addressed.
Soil Syst. 2018, 2(3), 45;
Received: 3 June 2018 / Revised: 11 July 2018 / Accepted: 24 July 2018 / Published: 1 August 2018
(This article belongs to the Special Issue Soil Processes Controlling Contaminant Dynamics)
Phosphorus (P) is an essential nutrient for sustaining life and agricultural production. Transformation of readily available P into forms that are unavailable to plants adds costs to P replenishment, which eventually translates into lower agronomic benefits and potential loss of soil P into runoff may degrade water quality. Therefore, understanding the sources and pathways of the formation of residual P pools in soils is useful information needed for the development of any technological or management efforts to minimize or inhibit the formation of such P pool and thus maximize availability to plants. In this research, we paired phosphate oxygen isotope ratios (δ18OP) with solid-state 31P NMR and quantitative XRD techniques along with general soil chemistry methods to identify the precipitation pathways of acid-extracted inorganic P (Pi) pools in an agricultural soil. Based on the comparison of isotope values of 0.5 mol L−1 NaOH-Pi, 1 mol L−1 HCl-Pi, and 10 mol L−1 HNO3-Pi pools and correlations of associated elements (Ca, Fe, and Al) in these pools, the HNO3-Pi pool appears most likely to be transformed from the NaOH-Pi pool. A narrow range of isotope values of acid-Pi pools in shallow (tilling depth) and below (where physical mixing is absent) is intriguing but likely suggests leaching of particle-bound P in deeper soils. Overall, these findings provide an improved understanding of the sources, transport, and transformation of acid-Pi pools in agricultural soils and further insights into the buildup of legacy P in soils. View Full-Text
Keywords: phosphate; oxygen isotopes; solid-state NMR; XRD; soil-P pools; transformation phosphate; oxygen isotopes; solid-state NMR; XRD; soil-P pools; transformation
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Joshi, S.R.; Li, W.; Bowden, M.; Jaisi, D.P. Sources and Pathways of Formation of Recalcitrant and Residual Phosphorus in an Agricultural Soil. Soil Syst. 2018, 2, 45.

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