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Daniel C. Bowman, Richard Y. Evans, and Linda L. Dodge

A study was conducted to determine the potential for using ground automobile tires as a container medium amendment. Rooted cuttings of chrysanthemum [Dendranthema × grandiflorum (Ramat.) Kitamura] were planted in 1.56-liter pots containing 1 sand:2 sawdust (v/v) or media in which coarsely or finely ground particles of rubber substituted for 33%, 67%, or 100% of the sawdust. Amendment with the coarse material decreased total porosity and container capacity and increased air-filled porosity and bulk density relative to the sawdust control. Amending the medium with the fine material did not appreciably alter total porosity, container capacity, or bulk density, but did increase air-filled porosity. Plant height, fresh weight, dry weight, and number of open flowers were reduced significantly in rubber-amended media compared to sawdust controls. Rubber amendment reduced shoot tissue concentrations of N, P, K, Ca, Mg, and Cu, but increased Zn as much as 74-fold over control values. There was no accumulation of other heavy metals (Cd, Cr, Ni, Pb) or Na in the tissue due to rubber amendment. This study demonstrates that ground tires might be used as a component of container media in the production of greenhouse chrysanthemums. However, growth reductions and the potential for Zn toxicity may limit the usefulness of ground tires as a substitute for conventional organic amendments.

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Kimberly A. Klock-Moore and George E. Fitzpatrick

Analytical determination and confirmation of minimum compost processing times and minimum curing times can aid commercial growers in selecting compost materials that should give them more reliable and consistent results in their operations. Five-cubic-yard volumes of yard-trimmings were assembled into three 1.25-cubic-yard compost piles at 60-day intervals. At the conclusion of the experiment, there were three piles each of compost of the following ages: 10 months, 8 months, 6 months, and 2 months. Compost was collected from each pile and screened through a 0.75-inch screen. Bulk density, water-holding capacity, air-filled porosity, carbon to nitrogen ratio, electrical conductivity, and ATPase activity were determined on samples from each reference compost pile. A bioassay using beans also was performed. These data will be presented.

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S.B. Wilson, P.J. Stoffella, and D.A. Graetz

Growth of golden shrimp plant (Pachystachys lutea Nees.) transplants was evaluated in media containing 0%, 25%, 50%, 75%, or 100% compost derived from biosolids and yard trimmings. A commercial coir- or peat-based media was amended with compost. As compost composition in the peat or coir-based media increased from 0% to 100%, carbon/nitrogen ratios decreased; and media stability, nitrogen mobilization, pH, and electrical conductivity increased. Bulk density, particle density, air-filled porosity, container capacity, and total porosity increased as more compost was added to either peat- or coir-based media. Plants grown in media with high volumes of compost (75% or 100%) had less leaf area and lower shoot and root dry weight compared to the controls (no compost). Regardless of percentage of compost composition in either peat or coir-based media, all plants were considered marketable after 8 weeks.

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David R. Hershey

Abstract

One of the most important aspects of the physics of growing media in containers is the limited bulk volume of the medium (2,4). Bulk volume (BV) includes the volume of the medium solids and pore spaces (1). Despite the importance of BV in determining the amounts of air, water, and nutrients in the pot, BV is rarely specified in research articles involving plant growth in container media. Without BV, volumetric properties, such as bulk density (g/ml), container capacity (percent by volume), air-filled porosity (percent by volume) and fertilization and liming rates (kg/m3), cannot be converted to absolute amounts per pot. The purpose of this study was to develop equations to calculate BV using pot dimensions and medium height in the pot.

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Nektarios Panayiotis, Tsiotsiopoulou Panayiota, and Chronopoulos Ioannis

Four substrates were investigated for their efficacy as roof garden vegetative layers. The substrates comprised a sandy loam soil (S), sandy loam soil amended with urea formaldehyde resin foam (S:F) in a proportion of 60-40 v/v, sandy loam soil amended with peat and perlite (S:P:Per) in a proportion of 50-30-20 v/v and peat amended with urea formaldehyde resin foam (P:F) in a proportion of 60-40 v/v. The substrates were evaluated for their physical and chemical properties and their capacity to sustain growth of Lantana camara L. Physical and chemical evaluation included weight determination at saturation and at field capacity, bulk density determination, water retention, air filled porosity at 40 cm, pH and EC. When compared to the control (S) a weight reduction of 16.8%, 23.9% and 70.3% was obtained at field capacity with S:F, S:P:Per and P:F substrates respectively. Bulk density was reduced by 46%, 43% and 95%, in substrates S:F, S:P:Per and P:F, respectively, compared to the control substrate S. Air-filled porosity at 40 cm was slightly increased for substrate S:F while it was substantially increased for substrate P:F. The pH response between the initiation and the termination of the study was similar for the four substrates. EC decreased in substrates S and S:P:Per but increased in substrates S:F and P:F. Plant growth was monitored as shoot length, shoot number, main shoot diameter and the number of buds and flowers. Substrates S and S:F resulted in similar plant growth, while substrate S:F promoted flowering. Substrate S:P:Per induced slow plant growth during the first 6 months which subsequently increased resulting in a final growth that was satisfactory and comparable to the S and S:F substrates. Substrate P:F did not support sufficient plant growth and its use should be considered only in special cases where reduced weight of the roof garden is imperative.

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Nsalambi Nkongolo, Jean Caron, and Fabienne Gauthier

Increasing rates (5%, 10%, 25%, and 40%, v/v) of six sources of organic wastes were substituted for peat to assess changes on the physical properties of peat–perlite media and the subsequent plant response. Wastes were both fresh and composted bio-filter, sewage sludge, and de-inked paper sludge. Geranium plants (Pelagornium ×hortum `Orbit Hot Pink') were grown in the media. Saturated hydraulic conductivity (Ksat) and air-filled porosity (AFP) were successively measured with a Cote infiltrometer and by time-domain reflectometry. Pore space tortuosity (PST) and gas relative diffusivity (Dp/Do) were calculated. Both physical and plant growth parameters were significantly affected by the source and rate of application of waste. Ksat (P = 0.0001, r = 0.937), AFP (P = 0.001, r = 0.984), PST (P = 0.0001, r = 0.935), Dp/Do (P = 0.0001, r - 0.872) linearly increased as the rate of waste increased in the media. However, plant height (P = 0.0001, r = 0.856), root dry weight (P = 0.0001, r = 0.994), and shoot dry weight (P = 0.0001, r = 0.963) either linearly or quadratically decreased as the rate of waste increased. Decreases in plant growth parameters were most likely due to high salinity of organic wastes.

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E. Jay Holcomb, Robert Berghage, and William Fonteno

The concepts of container water-holding capacity and air-filled porosity are important yet complicated for students interested in containerized crop production; however, both of these concepts can be observed and understood more completely if students develop a moisture retention curve. Our objectives were to describe an easy-to-construct and economical apparatus for creating a moisture retention curve and then to compare this curve with one generated by standard methods. The student method (column method) is constructed from plastic pipe cut into 5-cm sections. The sections of pipe are individually packed with a substrate then stacked and taped together, resulting in a 60-cm column of the substrate. The column is saturated and allowed to drain for 24 h. Then, the column is taken apart and the water content of each section determined gravimetrically. The water content of each section is graphed against height so that the result is a moisture retention curve. Data are presented to show the curve developed from the column method is similar to the curve developed by standard soil moisture tension method. The moisture retention curve can provide a better understanding of water and air holding capacities of substrates.

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Craig Dilley and Gail Nonnecke

Sustainable strawberry production depends on effective weed and soil management. Alternative weed management strategies are needed because few herbicides are registered for use in matted-row strawberry culture. Soil analyses are often measured in terms of chemical and physical properties alone. Measuring biological indicators of soil quality that are sensitive to changes in the environment can enhance these analyses. The experiment compared the effects of four weed management systems on weed growth, soil quality properties, and strawberry yield, growth, and development. Treatments were killed-cover crop mixture of hairy vetch (Viciavillosa) and cereal rye (Secalecereale); compost + corn gluten meal + straw mulch; conventional herbicide; and methyl bromide soil fumigation. Results indicated that there were no differences in percentage of weed cover or number of strawberry runners between the four weed management treatments in the planting year (July or Aug. 2004). The soil quality parameters, infiltration rate, soil bulk density, earthworm number, and total porosity were similar for all treatments. Plots that received the straw mulch treatment had a soil volumetric water content 20% higher and air-filled porosity that was 26% higher than the average of other treatments. Although treatment plots received similar N, leaf nutrient analysis showed that plants receiving the straw mulch + corn gluten meal treatment had a similar amount of total N when compared to the conventional and methyl bromide treatments, but was 21% higher than the killed-cover crop treatment.

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Calvin Chong* and Adam Dale

Terminal stem cuttings of seven woody nursery species [boxwood (Buxus sempervirens L. `Green Mountain'), coralberry (Symphoricarpus × chenaultii Rehd. `Hancock'), lilac (Syringa velutina Kom.), Peegee hydrangea (Hydrangea paniculata Siebold. `Grandiflora'), purple-leaf sandcherry (Prunus × cistena N.E. Hansen), Rose-of-Sharon (Hibiscus syriacus L. `Lucy'), and winged spindle-tree (Euonymus alata Thunb.) Siebold. `Compacta')] were rooted under outdoor lath (50% shade) and mist in leached rooting media consisting of 0, 20, 40, 60 and 80% by volume of 2-year-old grape pomace amended in binary mixtures with sphagnum peat, perlite or composted bark. Rooting performance, expressed in terms of percent rooting, mean root number per rooted cutting, and length of the longest root per cutting, was regressed on level of pomace. When there were differences due to amendments, most species rooted better with perlite than with bark and peat, to a lesser degree, due in part to more favourable air-filled porosities with perlite (33% to 42%) than with bark (29% to 37%) or peat (24% to 35%). With boxwood, increasing level of pomace up to ≈60%, especially when mixed with perlite or peat, resulted in substantial increases in rooting percentage, root number and length. All three rooting parameters of winged spindle-tree decreased linearly with increasing level of pomace with perlite or bark. The effect of pomace level on other species varied between these extremes with little or no negative effect on rooting.

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Sandra B. Wilson and Peter J. Stoffella

Peat is used extensively in the nursery industry as a primary component in commercial “soilless” potting media. The increased use of peat as an organic amendment with superior water-holding capacity is challenged by economic and environmental pressures. Developing inexpensive and nutrient-rich organic media alternatives can potentially reduce fertilization rates, irrigation rates, and ultimately, nursery costs. In addition, controversy over the effects of peat mining has inspired a national search for peat substitutes. With our burgeoning population, it is logical to screen waste products as potential alternatives to peat. Growth of Pachystachys lutea Nees. (Golden Shrimp Plant) transplants was evaluated in media containing 0%, 25%, 50%, 75%, or 100% compost derived from biosolids and yard trimmings. Compost was amended with a commercial peat- or coir-based media. As compost composition in the peat or coir-based media increased from 0% to 100%, carbon/nitrogen (C/N) ratios decreased, and media stability, N mobilization, pH, and electrical conductivity (EC) increased. Bulk density, particle density, air-filled porosity, container capacity, and total porosity increased as more compost was added to either peat- or coir-based media. Plants grown in media with high volumes of compost (75 or 100%) had reduced leaf area and reduced shoot and root DW than the controls (no compost). Regardless of percentage of compost composition in either peat or coir-based media, all plants were considered marketable after 8 weeks.