Soil Infrastructure, Interfaces & Translocation Processes in Inner Space (“Soil-it-is”): Towards a Road Map for the Constraints and Crossroads of Soil Architecture and Biophysical Processes

Soil functions and their impact on health, economy, and the environment are evident at the macro scale but determined at the micro scale, based on interactions between soil micro-architecture and the transport and transformation processes occurring in the soil infrastructure comprising pore and particle networks and at their interfaces. Soil structure formation and its resilience to disturbance are highly dynamic features affected by management (energy input), moisture (matric potential), and solids composition and complexation (organic matter and clay interactions). In this paper we review and put into perspective preliminary results of the newly started research program “Soil-it-is” on functional soil architecture. To identify and quantify biophysical constraints on soil structure changes and resilience, we claim that new approaches are needed to better interpret processes and parameters measured at the bulk soil scale and their links to the seemingly chaotic soil inner space behavior at the micro scale. As a first step, we revisit the soil matrix (solids phase) and pore system (water and air phases), constituting the complementary and interactive networks of soil infrastructure. For a field-pair with contrasting soil management, we suggest new ways of data analysis on measured soil-gas transport parameters at different moisture conditions to evaluate controls of soil matrix and pore network formation. Results imply that some soils form sponge-like pore networks (mostly healthy soils in terms of agricultural and environmental functions), while other soils form pipe-like structures (agriculturally poorly functioning soils), with the difference related to both complexation of organic matter and degradation of soil structure. The recently presented Dexter et al. (2008) threshold (ratio of clay to organic carbon of 10 kg kg-1) is found to be a promising constraint for a soil’s ability to maintain or regenerate functional structure. Next, we show the Dexter et al. (2008) threshold may also apply to hydrological and physical-chemical interface phenomena including soil-water repellency and sorption of volatile organic vapors (gas-water-solids interfaces) as well as polycyclic aromatic hydrocarbons (water-solids interfaces). However, data for differently-managed soils imply that energy input, soil-moisture status, and vegetation (quality of eluded organic matter) may be equally important constraints together with the complexation and degradation of organic carbon in deciding functional soil architecture and interface processes. Finally, we envision a road map to soil inner space where we search for the main controls of particle and pore network changes and structure build-up and resilience at each crossroad of biophysical parameters, where, for example, complexation between organic matter and clay, and moisture-induced changes from hydrophilic to hydrophobic surface conditions can play a role. We hypothesize that each crossroad (e.g. between organic carbon/clay ratio and matric potential) may control how soil self-organization will manifest itself at a given time as affected by gradients in energy and moisture from soil use and climate. The road map may serve as inspiration for renewed and multi-disciplinary focus on functional soil architecture

Searching the critical soil organic carbon threshold for satisfactory tilth conditions – test of the Dexter clay:carbon hypothesis

The concern for deteriorating soil structure at low soil organic matter (SOM) contents calls for better knowledge of SOM interaction with soil minerals as well as guidelines for soil conservation. We measured clay dispersibility in a field with a textural gradient. Our results support the concept of differentiating soil content of clay in a complexed and non-complexed part although our data did not point out an exact clay/OC ratio threshold. Our results also indicated that labile fractions of SOM may play an important role in soil physical behavior. We revisited literature data and found evidence that soil content of fines (<2 or <20 μm) is a major determinant of soil specific surface area (SA). We noted that soil SA coverage with SOM changed dramatically at a specific ratio of either clay (<2 μm) or clay+silt (<20 μm) with soil OC. This is an indirect support of the recently suggested quantification of the soil mineral ‘saturation’ hypothesis. More studies are needed on the causal relationships. We conclude that clay/OC~10 or (clay+silt20μm)/OC~20 are corresponding indices reflecting shift in soil physical behavior

Gas transport in partially-saturated sand packs

Understanding gas transport in porous media and its mechanism has broad applications in various research areas, such as carbon sequestration in deep saline aquifers and gas explorations in reservoir rocks. Gas transport is mainly controlled by pore space geometrical and morphological characteristics. In this study, we apply a physically-based model developed using concepts from percolation theory (PT) and the effective-medium approximation (EMA) to better understand diffusion and permeability of gas in packings of angular and rounded sand grains as well as glass beads. Two average sizes of grain i.e., 0.3 and 0.5 mm were used to pack sands in a column of 6 cm height and 4.9 cm diameter so that the total porosity of all packs was near 0.4. Water content, gas-filled porosity (also known as gas content), gas diffusion, and gas permeability were measured at different capillary pressures. The X-ray computed tomography method and the 3DMA-Rock software package were applied to determine the average pore coordination number z. Results showed that both saturation-dependent diffusion and permeability of gas showed almost linear behavior at higher gas-filled porosities, while deviated substantially from linear scaling at lower gas saturations. Comparing the theory with the diffusion and permeability experiments showed that the determined value of z ranged between 2.8 and 5.3, not greatly different from X-ray computed tomography results. The obtained results clearly indicate that the effect of the pore-throat size distribution on gas diffusion and permeability was minimal in these sand and glass bead packs

Prediction of biopore- and matrix-dominated flow from X-ray CT-derived macropore network characteristics

Peer reviewedPublisher PD

Tillitsmodellen. En empirisk studie fra hjemmebaserte tjenester om ansattes erfaringer med tillitsmodellen i Oslo kommune.

Etter snart 20 år med bestiller- utfører modellen som fungerende tjenestemodell med sterk påvirkning fra New Public Management reformene mente lokalpolitikerne i Oslo kommune at det var tid for endring. To demografiske trender; økning i antall eldre og urbanisering gjorde at man ønsket å imøtekomme dette ved å utvikle en innovativ løsning for tjenesten. Politikerne ønsket en avbyråkratisering av tjenesteproduksjonen med mindre kontroll. Den hjemmebaserte tjenesten ble kritisert for å være rigid og uten mulighet for å yte faglig skjønn i møte med brukeren brukerne. Som et resultat valgte politikerne å utvikle en tillitsmodell for Oslo kommune. Det overordnede tema for denne oppgaven er tillitsmodellen, og hvordan den praktiseres i hjemmebaserte tjenester i Oslo kommune. Et mål for tillitsmodellen i Oslo var å gi større myndig og faglig tillit til ansatte, og derved økt kompetanse, motivasjon og arbeidsglede. Et annet sentralt mål var brukerfokus i tjenesten med større fleksibilitet, kvalitet og økt tilfredshet med tjenesten for bruker. Hensikten med studien er å utvikle kunnskap om et nytt felt innen hjemmebaserte tjenester. Studien vil omfatte ansattes erfaringer med tillitsmodellen, knyttet til tverrfaglige teams og brukermedvirkning. Det er valgt en kvalitativ metode for studien da det var et ønske å gå i dybden og få frem nyanserte data i et lite utvalg. Data ble innhentet gjennom individuelle intervjuer av ansatte fra tverrfaglige team. Resultater knyttet til tverrfaglige team: Studien viser at ansattes roller og ansvar hadde endret seg etter implementeringen av tillitsmodellen. Ansatte opplevde en større grad av autonomi og tillit til å ta beslutninger som ga dem motivasjon og engasjement i tjenesten. Tillitsmodellen ga større grad av kontinuitet og fleksibilitet. Det tverrfaglige samarbeide fremmet av tillitsmodellen styrket kompetansen og kvaliteten på tjenesten. Studien fremhevet at tillit og kontroll kan fungere sammen, men at kontrollen må gi mening og være begrunnet, ellers kan det føre til mistillit. Resultater knyttet til brukermedvirkning: Tillitsmodellen ga en bedre relasjon og nærhet mellom ansatte og brukere. Dette ble blant annet skapt når spørsmålet «Hva er viktig for deg?» ble stilt. En utfordring og bekymring ble vist de sårbare gruppene i tjenesten som ikke klarte å sette ord på egne ønsker og behov. Studien viser at ansatte opplevde at tillitsmodellen oppfordret til høy grad av brukermedvirkning. Dette var på tross av at ingen hadde spurt brukeren om deres opplevelser