Changes in the soil structure and hydraulic conductivity of an Acidic Red Ferrosol were measured in a long-term (1968–2003) fertiliser experiment on pasture in north-western Tasmania, Australia. Studies were initiated following observations of both softer soil surface and cracking on plots that had received 15 t/ha of ground agricultural limestone. Liming decreased penetration resistance and increased hydraulic conductivity. These structural improvements were associated with increased mean dry aggregate size, a small increase in wet aggregate stability, higher exchangeable calcium levels, and increased plant growth, but a 9% decrease in total soil organic carbon in the surface 50 mm. This decrease in organic carbon was not associated with deterioration in soil structure, as may have been anticipated. This was probably because total organic C was still 82 g/kg on unlimed plots. Decreases in soil penetration resistance due to liming increased the likelihood of pugging from livestock but may improve ease of tillage. This research demonstrates that liming can improve the structure of a well-aggregated Ferrosol as well as its previously reported effects of increasing soil pH and yields of pasture and barley despite decreasing organic C.

Soil physical parameter calculation by inverse modelling provides an indirect way of estimating the unsaturated hydraulic properties of soils. However many measurements are needed to provide sufficient data to determine unknown parameters. The objective of this research was to assess the use of unsaturated water flow and solute transport experiments, in horizontal packed soil columns, to estimate the parameters that govern water flow and solute transport. The derived parameters are then used to predict water infiltration and solute migration in a repacked soil wedge. Horizontal columns packed with Red Ferrosol were used in a nitrate diffusion experiment to estimate either three or six parameters of the van Genuchten–Mualem equation while keeping residual and saturated water content, and saturated hydraulic conductivity fixed to independently measured values. These parameters were calculated using the inverse optimisation routines in Hydrus 1D. Nitrate concentrations measured along the horizontal soil columns were used to independently determine the Langmuir adsorption isotherm. The soil hydraulic properties described by the van Genuchten–Mualem equation, and the NO3– adsorption isotherm, were then used to predict water and NO3– distributions from a point-source in two 3D flow scenarios. The use of horizontal columns of repacked soil and inverse modelling to quantify the soil water retention curve was found to be a simple and effective method for determining soil hydraulic properties of Red Ferrosols. These generated parameters supported subsequent testing of interactive flow and reactive transport processes under dynamic flow conditions.

Nitrogen leaching in soils depends on the mobility of nitrate with, and relative to, water. This mobility is affected by anion adsorption at soil surfaces. Our work examines nitrate (NO3−) adsorption during non‐steady, unsaturated absorption of NO3− solution by columns of dry Red Ferrosol (Inceptic Eutrudox), approximating solute transport in unsaturated field soils. The experiments, in which no water flows past the end of the column, show that the application of conventional water and reactive solute flow equations is valid. The profiles of water and NO3−, measured at different horizontal infiltration times, coalesce on to unique curves when plotted as a function of the Boltzmann variable, λ. Anion adsorption delays the NO3− advance relative to that of water. Pragmatically, we use Freundlich and Langmuir equations as convenient mathematical descriptions of how the NO3− is partitioned between the soluble and adsorbed concentrations and conclude that the latter is appropriate for our dataset. We advocate the use of the Langmuir equation (non‐linear form) to obtain the fitting parameters to avoid the need to use ratios of small values, which results in large errors. Absorption of a solution into unsaturated columns of soil provides a powerful method for exploring adsorption: the experiment implicitly tests the water flow equation, the salt flow equation and solute equilibrium between the water‐soluble and adsorbed phases.