Wettability of crushed air-dried minerals

published_or_final_versio

Rethinking soil water repellency and its management

Soil water repellency (SWR) is a widespread challenge to plant establishment and growth. Despite considerable research, it remains a recalcitrant problem for which few alleviation technologies or solutions have been developed. Previous research has focused on SWR as a problem to be overcome, however, it is an inherent feature of many native ecosystems where it contributes to ecosystem functions. Therefore, we propose a shift in the way SWR is perceived in agriculture and in ecological restoration, from a problem to be solved, to an opportunity to be harnessed. A new focus on potential ecological benefits of SWR is particularly timely given increasing incidence, frequency and severity of hotter droughts in many regions of the world. Our new way of conceptualising SWR seeks to understand how SWR can be temporarily alleviated at a micro-scale to successfully establish plants, and then harnessed in the longer term and at larger spatial scales to enhance soil water storage to act as a “drought-proofing” tool for plant survival in water-limited soils. For this to occur, we suggest research focusing on the alignment of physico-chemical and microbial properties and dynamics of SWR and, based on this mechanistic understanding, create products and interventions to improve success of plant establishment in agriculture, restoration and conservation contexts. In this paper, we outline the rationale for a new way of conceptualising SWR, and the research priorities needed to fill critical knowledge gaps in order to harness the ecological benefits from managing SWR

Physical properties controlling water repellency in synthesized granular solids

The wettability of granular solids such as soil is known to depend primarily on two factors: their inherent chemistry and their physical properties, such as their particle size, particle shape and surface roughness. Nevertheless, the distinctive physical properties of such materials have not been fully explored to gauge their wettability. In this study, the difference in wettability between a flat solid (microscope slide) and three granular solids, namely glass beads (GB), Leighton Buzzard Sand (LBS) and crushed Glass (CG), which have different physical properties, were examined. The effect of chemistry was isolated by strongly hydrophobizing the above materials by treatment with dimethyldichlorosilane. Wettability measurements were made by measuring the water–solid contact angle (CA) by the sessile drop method after adhering one layer of uniformly oriented granular solids on to double‐sided adhesive tape initially attached to a microscope slide. Techniques for particle characterization included sieving for particle size, dynamic image analysis for particle shape and confocal laser microscopy to determine surface roughness. Results show that all CAs of the granular solids exceeded that of the hydrophobized microscope slide (103°). The crushed glass had the largest CA (125°). With all three granular solids, there was an increase in CAs as particle size decreased. In addition, as particles became more angular, CAs increased. The influence of shape on wettability became more predominant as particle size decreased. The surface roughness parameter, Ra, was investigated and shown to be sensitive to both the size and shape of the particles. A decrease in Ra from 95.4 to 34.1 μm increased CAs from 107 to 125°. A similar change in CA was shown to correspond to an increase in void fraction from 40.7 to 77.4%. Our results have practical implications for the optimum use of soil by enhancing or suppressing water repellency