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.
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.