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Soil water repellency, that is, the reduced ability of soils to absorb water, is thought to be caused by organic coatings with predominantly non‐polar properties on soil particle surfaces. Given the important role of particle surface polarity in determining soil water repellency, we explored the use of fluorescent probes as a method for the direct in‐situ determination of the distribution and polarity of organics on bulk soil surfaces, and of their molecular mobility. We used nile red and pyrene, which have both been used successfully as environmental probes in previous studies, but have not been applied before to bulk soils. The probes were either (a) co‐deposited with other organics known to induce water‐repellent behaviour with acid‐washed sand to produce 'model soils' or (b) adsorbed directly onto sandy soils that were naturally water repellent to different degrees, and studied using fluorescence microscopy and steady‐state and time‐resolved fluorescence. Reliable measurements could be made using pyrene as an in‐situ probe on both model and natural soils, and a viscosity/mobility probe on model soils, whereas nile red was found not to be a useful probe. On model soils, made using hexadecane (HEX), octadecane (OCT) or stearic acid (SA) on acid‐washed sand, pyrene excimer formation kinetics showed a decrease in environment mobility as the organic layer changes from a liquid through to a hard wax. Spectra from pyrene adsorbed to natural soils indicated varying environmental polarity and heterogeneity within the soil samples studied. Highlights: Exploration of in‐situ fluorescent probes to study polarity and viscosity of organics on soils.Fluorescent probes have never been used in situ on bulk soils before.Pyrene probe shows variation in mobility, polarity and heterogeneity of organics on soils.Pyrene is a useful in‐situ fluorescent probe of polarity and mobility of organics on soils. [ABSTRACT FROM AUTHOR]

• Rough surfaces, e.g. soils, exhibit anomalously high contact angles. • A geometric correction, not invoking Cassie‐Baxter or Wenzel theories, is presented. • Its validity is shown experimentally using precise arrays of model substrates. • Implications for contact angle measurements in soil studies are presented. Anomalously high water contact angles are often measured for soils or other granular materials when using a goniometer which is designed for use with flat surfaces. For many years such high contact angles have been rationalised in terms of Cassie and Baxter, and/or Wenzel models for contact angles on non‐planar surfaces, but it is becoming increasingly apparent that the theories behind these models are fundamentally flawed. Here, we present an alternative interpretation of these anomalously high contact angles which takes into consideration how a water drop sits on the particulate surface, and propose a geometric correction factor to address this anomaly. Experimental data from studies with precisely arranged needles and spheres, and model and natural soils, were used to explore this approach and examine the validity of the method. Application of the correction factor to measurements of water drops on 1 mm diameter steel spheres hydrophobised with paraffin wax gave a reduction of the measured contact angle of 140.4(±0.6)° to a corrected contact angle of 108.2(±1.0)°, which is within 3.5° of the flat‐plane contact angle for water on the wax of 111.7(±0.6)°. For paraffin wax coated soils, measured contact angles are shown to be 15–25° higher than comparable flat-plane contact angle. This correction factor may be useful in interpreting goniometer contact angle measurements of irregular surfaces since it is the flat-plane, rather than measured, contact angle which gives a measure of the polarity/hydrophobicity of the surface. [ABSTRACT FROM AUTHOR]