Boudreau, J., Caron, J., Elrick, D., Fortin, J. and Gallichand, J. 2009. Solute transport in sub-irrigated peat-based growing media. Can. J. Soil Sci. 89: 301-313 New legislation to reduce the amount of fertilizer leached into the environment by horticultural growers and the need to implement water-saving irrigation systems require an understanding of salt build-up and of nutrient cycles in order to develop efficient water-use strategies for growers. Solute transport in growing media is central to this process, but has received little attention thus far. The objectives of this study were to determine how solutes behave in sub-irrigated growing media and to assess a solute transport model for these media. A steady state evaporation (upward water flow) experiment was carried out with three different growing media in packed columns in the laboratory. Bromide, potassium and copper concentrations were determined using in-column pore water solution samplers and by sectioning the columns at the end of the experiment to obtain concentration profiles. The Hydrus-1D model was fitted to the solution sampler data assuming non-linear Freundlich adsorption, and then used to obtain favorable predictions of the measured concentration profiles. Independent adsorption isotherm results from batch experiments were found to be inadequate when used to predict Solute movement and the results indicate that the preferred approach is an in-column evaluation of the transport parameters.

Reducing irrigation in nursery production has become a major issue due to environmental concerns. Different irrigation systems are proposed to increase irrigation efficiency. These systems required growing media with specific properties to optimize their utilization. Substrates commonly used are often too coarse resulting in frequent watering and poor capillarity properties required for sub-irrigation systems. Addition of Sphagnum peat could enhance water holding capacity and reduce water use. An experiment was conducted to evaluate water-saving potential of Sphagnum peat (30 to 60%) in a bark mix (30 to 60% bark/10% sand) compared to sedge peat (30%) commonly used in Florida. The setup included both overhead irrigation and capillary mat system (Aquamat) in nursery production of Ligustrum and Viburnum. Plant growth was improved using Sphagnum peat in high proportion reducing production time (13 to 28%) and water use (15 to 38%) with both irrigation systems. The best combination tested was capillary mat used with the substrate containing 60% Sphagnum peat which provided an adequate capillary rise. An economic analysis showed the profitability of this solution and definitely justified the additional investments required.

Simplified measurements of the field‐saturated hydraulic conductivity, Kfs, require short duration experiments, small water volumes, and easily transportable equipment. A simplified falling‐head (SFH) technique for the rapid determination of Kfs has been developed and tested. The technique consists in applying a small volume of water on a soil surface, confined by a ring inserted a short distance into the soil, and then measuring the time from the application of water to the instant at which the surface area is no longer covered by water. A measurement of the initial and field‐saturated soil water contents, and an estimate of the α* parameter of the Gardner's exponential model are then used to calculate Kfs using a simple solution that includes gravity. The Kfs of both repacked and undisturbed soil cores was determined in the laboratory by the SFH and the early time constant‐head (ECH) techniques. The SFH and (constant‐head) pressure infiltrometer (PI) techniques were then compared in the field. The maximum discrepancy between the mean Kfs results obtained within an experiment was of a factor of approximately two. This difference is negligible in most practical applications and it was concluded that the SFH technique compared favorably with the ECH technique in the laboratory and to the PI technique in the field. The SFH technique appears promising for determining Kfs in a relatively short period of time without the need for extensive instrumentation or analytical methodology, and therefore it appears suitable for detailed field measurements over large areas.

Analytical solutions of the flow equation for infiltration offer an interesting tool for the hydrodynamic characterization of non-saturated soils by optimization of the hydraulic conductivity, Kfs, and the capillary sorptivity, So. However, the experimental conditions have to satisfy the governing assumptions. For falling head infiltration tests the initial water height, Ho, is a third unknown parameter that has to be optimized. For the short-time, the classic solution expresses the depth of water infiltrated as a function of time as a term that depends only on the sorptivity. This, however, neglects gravitational effects. We improved the falling head infiltration problem, after a period of constant head infiltration, for the case of rigid materials without any assumptions for a particular hydraulic conductivity relationship and taking into account gravity effects. A comparison of two solutions, i.e., the equation of one and two terms, was made using the results of falling head infiltration tests. Neglecting the effects of gravity in the infiltration equation leads to an overestimation of the hydrodynamic parameters, Ho and So, and a concomitant underestimation of Kfs compared to our improved solution developed here. Consequently, the depth of ponded water predicted by the one term infiltration equation is higher than that calculated by the improved two term solution. Unfortunately, the actual depth of water infiltrated into the soil cannot be independently verified. To accomplish this, it is recommended that future studies include a measure of the change in stored soil water content at the test site, or a continuous measure of the variation in soil water content by a non-destructive method.

James and Verspagen (1996), Thompson andJames (1995), andShahin ( 1994) have observed low runoff volumes from porous concrete paver laboratory test blocks used in their respective research.However, the laboratory test blocks were not subjected to wear or the deposition of pollutants over time on the surface and, therefore, perform under optimum conditions.The purpose ofthis research is to test the hypothesis that, for a particular permeable paver hereinafter called Uni-ecostone (see acknowledgements at end for trademarks), infiltration capacities decrease with age and certain land uses, and that infiltration capacities may be improved by simply street sweeping and/or vacuuming the surface.The research uses data collected at several Uni-ecostone porous concrete paver installations.Permeable pavement helps reproduce the pre-development hydrologic regime at urbanized sites (Schueler, 1987).In achieving this, the key is to provide a surface infiltration capacity which allows an adequate volume of stotmwater runoff to be captured by the facility.Such an infiltration capacity is dependent upon factors such as surface slope, and surface ponding.There is little difficulty in designing and constructing a system to provide appropriately high infiltration capacities; however, maintaining these infiltration capacities over several years has proven to be challenging.

A simple analytical expression is derived to describe soil water profiles satisfying the Bruce and Klute equation. Two parameters have to be determined from integral conditions. The simplicity and accuracy of the technique is checked when the soil-water diffusivity obeys an exponential or a power law function. For those two examples no numerical work is necessary as the results are expressed in terms of tabulated functions only. The method extends to the profile determination the optimal technique used earlier for the determination of the sorptivity, with the same precision.