Toyon [Heteromeles arbutifolia (Ait.) M.J. Roemer] cuttings were grown in container media having air-filled porosity (Ea) values ranging from 1% to 20%. Plants were inoculated with Phytophthora cinnamomi Rands zoospores, and all media were maintained at or near container capacity for 3 weeks, after which plants were evaluated for root rot symptoms. Inoculated plants grown in media with <10% Ea developed severe root rot, while those grown in media having Ea values of 10-20% appeared relatively healthy. Roots of noninoculated plants growing in low-Ea media were not adversely affected during the experimental period.
A 2-year experiment with Prunus ×cistena sp. was conducted in pots using seven substrates composed of various proportions of primarily peat, compost and bark. Peat substrates significantly affected root and shoot dry weight. Water desorption characteristics and saturated hydraulic conductivity were measured in situ to estimate the pore tortuosity factor and the relative gas diffusion coefficient. The pH, electrical conductivity, C/N ratio, total and hydrolyzable N, as well as NO3--N and NH4+-N in solution were also measured. Estimates of the physical properties suggest that a lack of aeration limited plant growth. Plant growth was significantly correlated with both the gas relative diffusivity and the pore tortuosity factor. Among the chemical factors, pH and soil nitrate level were also correlated with plant growth. No significant correlation was found between plant growth and air-filled porosity or any other measured chemical properties. This study indicates that an index of gas-exchange dynamics could be a useful complementary diagnostic tool to guide substrate manufacturing.
Root regeneration from root cuttings of both difficult-to-transplant Pistacia chinensis and moderately easy-to-transplant Liquidambar styraciflua was studied in a sphagnum peat medium varying from 0-100% Ca saturation and from 0-50% air filled porosity. Maximum root regeneration of Pistacia root cuttings was obtained at 75% Ca saturation and 30% and 40% air filled porosity, whereas Liquidambar root cuttings regenerated roots best at 25% Ca saturation and at 20% to 40% air filled porosity. Indolebutyric acid applied to the root cuttings greatly increased root-regenerating potential of Pistacia root cuttings but did not affect the optimum Ca and aeration requirement(s). Similarly, indolebutyric acid treatment greatly promoted the root-regeneration potential of Liquidambar root cuttings. Satisfactory root-regenerating conditions of both Ca saturation and air filled porosity for Liquidambar root cuttings were a little broadened by indolebutyric acid (IBA) application.
Pistacia bare root seedlings also required high levels of Ca saturation and aeration for optimum root regeneration. Considerably greater numbers of roots were regenerated in peat having 75% Ca saturation and 20% air filled porosity than in peat having 0% Ca saturation and 5% air filled porosity. Root regeneration was not improved by increasing only the air filled porosity when Ca was low.
Chrysanthemum morifolium cv. Brilliant Anne was grown in 13 different media under frequent irrigation such that all media were nominally at container capacity. Media were selected to represent a range in airfilled porosity (0–20%) at container capacity with a depth of 12 cm. Substantial addition of organic amendment (40–90% v/v) improved aeration in a poorly aggregated loam and in two sands. Peat plus vermiculite had the best aeration of all media. Thirty day top yields were related to aeration properties of the media measured at container capacity. A value of 10–15% air-filled porosity was generally related to best growth. Oxygen diffusion rate (ODR) for the medium profile provided a better correlation with plant growth than air-filled porosity. A profile ODR of 45g O2 × 10‒8 cm-2 min-1 and above gave best growth.
This paper describes a system for predicting container mixture physical and chemical properties from component properties. An additive model is presented that assumes that a mixture property is the weighted sum of the properties contributed by the individual components. To test this hypothesis, 24 combinations of sandy loam soil (Typic Xerothent), sand (Typic Xeropsamment), bark, and perlite were tested for bulk density, total and air-filled porosities, container capacity, available water, saturated hydraulic conductivity, pH, and cation exchange capacity. The measured experimental data were compared with values predicted from the additive model. Measured and predicted values were in good agreement for most properties, except saturated hydraulic conductivity and air-filled porosity for mixtures with low total porosity. Application of the same approach also worked well for previously published data.
an extensive list of abiotic factors that influence root growth in containers in their review. Among them, the physical properties of growing substrate are of great importance. The air-filledporosity and the water retention capacity and availability
size range and distribution. Furthermore, the actual container capacity of a containerized substrate, and thus the air-filledporosity and the water-holding capacity, depend on container height ( Fonteno, 1996 ; Milks et al., 1989b ). Hence, the
well-known for their large particle sizes, which create high air-filledporosity and low water-holding capacity, when compared with other horticultural substrates such as peat or coir ( Raviv and Leith 2008 ). A careful balance between a particle size
A new tube method for determining physical properties in container substrates was compared to an existing system. While both offer the advantages of undisturbed substrate and measurement of properties without altering the geometry of the substrate in the container, the tube method is easier to conduct. Both methods proved equally effective for determining air-tilled porosity, container capacity, total porosity, bulk density, and particle density.
Two commercially produced growth media made of light, low humified sphagnum peat, were used to determine how filling into containers affects the particle size distribution and water retention characteristics of peat. It was shown that the filling procedure used broke up the peat particles, resulting in a significant increase in the proportion of particles < 1 mm (g·g-1). Due to the increased proportion of fine particles, the water retention of the peat media increased under wet conditions (-0.1 kPa matric potential), while the air-filled porosity decreased to nearly 0. Also, at matric potentials lower than -0.1 kPa, the reduction in air-filled porosity may restrict aeration and availability of oxygen to roots, thus reducing growth of plants.