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Open AccessArticle

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

1
Department of Plant and Soil Sciences, University of Delaware, Newark, DE 19716, USA
2
Key Lab for Surficial Geochemistry (MOE), School of Earth Science and Engineering, Nanjing University, Nanjing 210023, China
3
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; https://doi.org/10.3390/soilsystems2030045
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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