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The fractionation factors associated with denitrification, determined under oxic incubation, are similar to the factors previously determined under anoxic conditions, hence potentially applicable for field studies. However, it was shown that the η(18)O/η(15)N ratios, previously accepted as typical for N2O reduction processes (i.e., higher than 2), are not valid for all conditions.

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[1] Measurements have been made of the effect of compaction on water retention, saturated hydraulic conductivity, and porosity of two English soils: North Wyke (NW) grassland clay topsoil and Broadbalk silty topsoil, fertilized inorganically (PKMg) or with farmyard manure (FYM). As expected, the FYM topsoil had greater porosity and greater water retention than PKMg topsoil, and the NW clay topsoil retained more water at each matric potential than the silty topsoils. Compaction had a clear effect on water retention at matric potentials wetter than −10 kPa for the PKMg and FYM soils, corresponding to voids greater than 30 mm cylindrical diameter, whereas smaller voids appeared to be unaffected. The Pore-Cor void network model has been improved by including a Euler beta distribution to describe the sizes of the narrow interconnections, termed throats. The model revealed a change from bimodal to unimodal throat size distributions on compaction, as well as a reduction in sizes overall. It also matched the water retention curves more closely than van Genuchten fits and correctly predicted changes in saturated hydraulic conductivity better than those predicted by a prior statistical approach. However, the changes in hydraulic conductivity were masked by the stochastic variability of the model. Also, an artifact of the model, namely its inability to pack small features close together, caused incorrect increases in pore sizes on compaction. These deficiencies in the model demonstrate the need for an explicitly dual porous network model to account for the effects of compaction in soil.

Coated paper for high-quality printing comprises a fine particulate mineral coating, applied as an aqueous suspension and fixed to the fibrous paper substrate with a binder. The shrinkage occurring while the coating layer dries onto the substrate has been measured by observing the deflection of strips of a synthetic substrate coated with ground calcium carbonate with different binders. The force acting on the surface of the strips to cause a given deflection has been calculated using the elementary beam theory. The porosities of the dry structures were measured by compression-corrected mercury porosimetry. We show that the shrinkage occurring during the drying of the coating layer is mainly due to capillary forces acting as the water recedes in the porous structure, while the binder can act to retain the stress resulting from such forces. Starch produced much higher stresses than latex.

Summary We present a new method of characterizing the void structures of soils from water retention curves as the primary source of data. The method avoids the problems of other current approaches, which use smoothing curves and can miss the subtleties of soil structure, and usually ignore the shielding of large pores by the small connecting throats surrounding them. In the new method, software we have named ‘Pore‐Cor’ is used to generate simple three‐dimensional networks of voids that have the same water retention characteristics and porosities as the soils. To find the geometry of the required networks, we have introduced a Boltzmann‐annealed simplex which works in four parametric and three Boolean dimensions of parameter space. Also, a more robust measure of the difference between the experimental and simulated water retention curves has been developed. The method is applied to water retention curves for a wide range of English and Welsh soils, both experimental and generated from a pedotransfer function. The resulting simulated void structures have void sizes that change as expected across the soil texture diagram, have different structures as highlighted by the locations of retained water, but have connectivities (number of connecting throats per pore) that vary little. A wide range of other calculations of wetting and non‐wetting fluid transport properties, and calculations of the behaviour of fluid‐borne pollutants, are now possible. The main bar to further progress is a lack of sufficiently accurate and comprehensive data for water retention, and for saturated and unsaturated hydraulic conductivity.

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