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Slow diffusion and high fixation of phosphorus (P) in soils are major factors limiting its availability to plants. To develop efficient P management, monitoring the dynamics of P movement and availability is essential. However, most soil P tests are destructive, with coarse resolution. We developed a semi-quantitative nondestructive approach for determining labile soil P using ferrous oxide (FeO)-impregnated paper coupled with high-resolution imaging by scanning electron microscopy (SEM). The FeO paper was immersed in solutions containing different P concentrations and subjected to SEM equipped with energy-dispersive X-ray spectroscopy (EDS). Results showed high agreement between P extracted from the FeO papers and the SEM-EDS measurements (R2 = 0.96), indicating the approach's feasibility. Different SEM-EDS operational conditions were tested, and optimal conditions are described. We then applied the FeO-paper method to calcareous soil with added P and found good agreement with Olsen (R2 = 0.99) and FeO-gel (R2 = 0.96) extraction results. Finally, we created a high-resolution (sub-centimeter) map of labile P diffusing from P granules into calcareous, sandy, and acidic soils. The four repetitions (per soil) showed good agreement, with maximal percent deviation of <16%. Diffusion of P was limited to 10 mm from its point of application in calcareous soil, whereas it extended to ∼20 mm in the sandy and acidic soils. After 20 d, P lability dropped considerably in all soils, but the P-diffusion front extended further in the acidic and sandy soils than in calcareous soil. The study illustrates the feasibility of using FeO paper with SEM to generate 2D maps of P lability at sub-centimeter resolution.

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Generating a high-resolution map of labile soil phosphorus using ferrous oxide–impregnated paper combined with scanning electron microscopy
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Generating a high-resolution map of labile soil phosphorus using ferrous oxide–impregnated paper combined with scanning electron microscopy

Slow diffusion and high fixation of phosphorus (P) in soils are major factors limiting its availability to plants. To develop efficient P management, monitoring the dynamics of P movement and availability is essential. However, most soil P tests are destructive, with coarse resolution. We developed a semi-quantitative nondestructive approach for determining labile soil P using ferrous oxide (FeO)-impregnated paper coupled with high-resolution imaging by scanning electron microscopy (SEM). The FeO paper was immersed in solutions containing different P concentrations and subjected to SEM equipped with energy-dispersive X-ray spectroscopy (EDS). Results showed high agreement between P extracted from the FeO papers and the SEM-EDS measurements (R2 = 0.96), indicating the approach's feasibility. Different SEM-EDS operational conditions were tested, and optimal conditions are described. We then applied the FeO-paper method to calcareous soil with added P and found good agreement with Olsen (R2 = 0.99) and FeO-gel (R2 = 0.96) extraction results. Finally, we created a high-resolution (sub-centimeter) map of labile P diffusing from P granules into calcareous, sandy, and acidic soils. The four repetitions (per soil) showed good agreement, with maximal percent deviation of <16%. Diffusion of P was limited to 10 mm from its point of application in calcareous soil, whereas it extended to ∼20 mm in the sandy and acidic soils. After 20 d, P lability dropped considerably in all soils, but the P-diffusion front extended further in the acidic and sandy soils than in calcareous soil. The study illustrates the feasibility of using FeO paper with SEM to generate 2D maps of P lability at sub-centimeter resolution.

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