The air space fraction, or porosity, of plant roots is important to their internal aeration. Root porosity can be calculated from the following measurements: the weight of a sample of the roots in a pycnometer bottle filled with water; the weight of the root sample alone; the weight of the homogenate after ball milling the sample; and the weight of the bottle filled with water only. Results are variable and a mean of 10 samples must be obtained.

The unimpeded flow of water down through the soil is essential to agricultural production. Intensive cultivation can disrupt soil structure and restrict infiltration, which results in inefficient water and land use. In this review, the effects of organic matter on soil aggregation and water infiltration are discussed at several levels. Organic amendments (manure, plant residue, and synthetic polymers) are reported to increase soil organic matter (fulvic acids, humic acids, and polysaccharides) which binds soil particles together into aggregates. When soil structure is improved through aggregation, the resulting pore size distribution favors the downward flow of water in soil (infiltration). Mechanisms that link these components (e.g., organic amendments, polysaccharide production, aggregate formation, and increased infiltration) are suggested and management options that improve water infiltration rates are proposed.

A model proposed for predicting average values of solute concentration as a function of depth and time, based on a transfer function model, is tested on a field experiment over 1.44 ha. The experiment consisted of an initial calibration observing the transport of a concentrated solute pulse past 15 replicated solution samplers located at a depth Z = 30 cm. The model was subsequently used without further calibration to predict the shape of the pulse at 60, 90, 120, 180 cm, with good agreement between average predicted and measured values. A further test of the model was conducted by taking 36 soil cores between 180 and 360 cm at 170 days after the addition of the solute pulse to the soil surface. Good agreement was found between the predicted and observed depth of maximum concentration expressed as a relative probability.

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