Phosphorus (P) is an indispensable element for all life on Earth and, during the past decade, concerns about the future of its global supply have stimulated much research on soil P and method development. This review provides an overview of advanced state-of-the-art methods currently used in soil P research. These involve bulk and spatially resolved spectroscopic and spectrometric P speciation methods (1 and 2D NMR, IR, Raman, Q-TOF MS/MS, high resolution-MS, NanoSIMS, XRF, XPS, (µ)XAS) as well as methods for assessing soil P reactions (sorption isotherms, quantum-chemical modeling, microbial biomass P, enzymes activity, DGT, 33P isotopic exchange, 18O isotope ratios). Required experimental set-ups and the potentials and limitations of individual methods present a guide for the selection of most suitable methods or combinations.

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The adsorption behavior of a near-critical fluid (SF,) on a finely dispersed graphitic adsorbent (graphitized carbon black; Vulcan 3-G) has been studied. The surface excess concentration r was measured by approaching the critical point along near-critical isochores using a volumetric technique. From the scaling theory of critical adsorption by Fisher and de Gennes it is expected that r diverges at the critical point. At temperatures well above criticality of the fluid (T-Tc>3 K) we find the expected increase of r w i t h decreasing T; however, closer to T, the adsorption does not increase further but decreases sharply for T-tT,. This unexpected behavior was also found when the experiment was repeated under microgravity conditions on the space platform EURECA I. A similar maximum in T ( T ) was also observed for SF, adsorbed in a mesoporous controlled-pore glass with 31 nm mean pore diameter.

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