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Tianxia Wu and Judith A. Abbott

We compared the firmness and force relaxation characteristics of tomato flesh harvested at six maturity stages and stored intact or as 7-mm slices for 0 to 20 days. Three measurements were made on outer pericarp and columella tissue. A 4-mm cylindrical probe provided more consistent firmness measurements (lower percent CV) than a 6.4-mm spherical probe at harvest, and distances of 3 mm were more consistent than 1 mm. Following loading, stress relaxation was recorded for 10 s. Stored tomato samples were tested only with the 4-mm cylindrical probe and distance of 3 mm. Firmness was taken as the maximum force (Fmax) in the loading portion, usually occurring at 3 mm. Fmax of freshly harvested tomatoes ranged from 15 to 2 N for mature green and red tomatoes, respectively. Fmax was closely correlated to area, slope, and force at first peak, i.e., all four parameters measured the same physical property, and was moderately correlated (R > 0.9) to forces at specific relaxation times. Tomatoes stored intact generally had lower CVs than that of those sliced before storage, although there was little difference in average firmness (Fmax) between the two at a given storage time. A three-parameter model was developed to fit the relaxation curves. There was little correlation between Fmax and the three relaxation characteristics (R = 0.6 to 0.0), i.e., the relaxation characteristcs measured different physical properties than did Fmax. The responses of the relaxation characteristcs over storage time were dependent on the initial maturity of the tomatoes, but their values usually differed significantly between tomatoes stored intact or sliced, with tomatoes sliced before storage generally having higher values.

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Glenn R. Wehtje, Joey N. Shaw, Robert H. Walker, and Walker Williams

Various inorganic soil amendments have been promoted as a means of improving the chemical and physical properties of certain soils. To test this hypothesis, a marginally productive soil was supplemented with 20%, 40%, 60%, and 80% (v/v) of either selected inorganic amendments or sand. Amendments consisted of commercially available diatomaceous earth, calcined clay, zeolite, and crystalline SiO2. The soil material was extracted from the argillic horizon of a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludults). Ability of these soil-amendment mixtures to promote `Tifway' bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt Davy] growth was evaluated under greenhouse conditions, and contrasted to that obtained in nonamended soil. Selected chemical and physical properties that are pertinent to plant growth were also evaluated. The experiment, which was conducted 3×, began with a §60-day period in which both water and nutrients were optimum. This was followed by a 30-day drought. During optimum water and nutrients, no soil-amendment treatment(s) consistently resulted in superior bermudagrass growth compared to soil alone. However, <2% of the bermudagrass tissue that was produced during the drought became green and succulent with the resumption of irrigation in nonamended soil. This percentage was exceeded by all treatments that contained either ≥60% diatomaceous earth (Axis), or ≥40% calcined clay (Profile); and by 100% zeolite (Clinolite) and 100% silica (Green's Choice). Drought-sustaining ability of soil-amendment mixtures was significantly (P < 0.05) correlated with water-holding ability, soil strength, bulk density, and oxygen diffusion rate, but not correlated with either pH or cation exchange capacity (CEC). While certain inorganic amendments did improve the drought-sustaining ability of soil, the amount required was generally ≥40%.

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Michael Raviv

Compost is organic matter that has undergone partial thermophilic, aerobic decomposition. This environmentally safe process is called composting. The combination of raw materials and the chosen composting method yields a wide range of characteristics, such as organic matter (OM) content, nutrient content, potential for disease suppressiveness and other physical, chemical, and biological properties. The objectives of this review are describing the horticultural outlets for composts, defining compost characteristics important for the above uses, and describing composting procedures and raw materials leading to these characteristics. The two main horticultural uses of composts are as soil amendment and as an ingredient in container media. Soil-applied composts improve soil fertility mainly by increasing soil organic matter (SOM) that activates soil biota. Compost's nutrient content, and especially that of nitrogen (N), should be high (>1.8%). Composts having these characteristics are produced of raw materials rich in both OM and N, while minimizing their loss during composting. Typical raw materials for this purpose include animal manures, offal, abattoir residues, sewage sludge, and grass clippings. Various composting methods can yield the required results, including turned windrows, aerated static piles, and in-vessel composting. Composts are also used for substrates as low-cost peat substitute, potentially suppressive against various soilborne diseases. These composts must be stable and non-phytotoxic. Physical properties of compost used as substrate are important. Hydraulic conductivity, air porosity, and available water should be high. Reconciling the physical and biological demands may be difficult. Materials such as softwood bark, wood shavings, various types of shells or hulls, and coconut coir are characterized by good physical properties after composting. However, being relatively resistant to decomposition, these materials should be subjected to long and well-controlled composting, which may be shortened using N and N-rich organic matter such as animal manures. High temperatures [>65 °C (149.0 °F)] may cause ashing, which leads to reduced porosity. In addition to ligneous materials, composts serving as growing media may be produced from numerous organic wastes, such as manures, food industry wastes, etc. These materials are better composted in aerated static piles, which tend to minimize physical breakdown. Animal excreta are of special value for co-composting as they contain large, diverse populations of microorganisms, which accelerate the process.

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R. T. Fernandez, R. L. Perry, and D. C. Ferree

The 1980 NC-140 uniform apple rootstock trial plantings located in Michigan and Ohio were used to determine root distribution patterns of the nine rootstooks involved in the trial. The scion for the trial was Starkspur Supreme (Malus domestica Borkh.) on Ottawa 3, M.7 EMLA, M.9 EMLA, M.26 EMLA, M.27 EMLA, M.9, MAC 9, MAC 24 and OAR 1 rootstock. Trenches were established parrallel with the tree rows 0.8 m from the center of the trunks on both sides. The trenches were 1.5 to 2 m deep. Grids were constructed 1.2 m deep × 1.8 m wide with 30 cm × 30 cm grid squares. Soil was washed from the profile and the grid was placed over the profile. Roots were classified into 3 size categories; less than 2 mm, 2 to 5 mm and greater than 5 mm. Soil physical properties were also characterized. Differences were found between rootstock root distribution patterns and will be discussed in relation to rootstock and location/soil properties.

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Hazel Y. Wetzstein, Choongsik Kim, and Harry E. Sommer

Effects of autoclaving volume, gelling agent (Bactoagar, Gel-gro, Phytagar), and basal salts [Murashige and Skoog (MS); Woody Plant Medium (WPM); Gamborg B5 (GB)] on gel strength and pH of tissue culture media were tested. Gel strength was significantly affected by gelling agent and basal medium. MS media were generally softer than comparable WPM or GB media. As the vessel volume during autoclaving decreased, gel strength significantly decreased with Phytagar and Bactoagar gelling agents; Gel-gro had greater gel strength at the intermediate volume of medium autoclave. In all cases, autoclaving resulted in a pH decrease of 0.2 to 0.5 pH units. Lower pH values were associated with softer gels. The type of gelling agent did not greatly affect the postautoclave pH; mean values among gelling agents were within 0.05 pH units. Postautoclave pH of MS medium was lower than that of WPM or GB. This study verifies the need to observe uniform sterilization protocols to maintain consistency in the chemical and physical properties of media.

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M.T. Kelley, G.C. Elliott, and R.J. McAvoy

Four different granulated rockwool (RW) aggregates were combined with peat at 15, 30, or 45 percent (v/v) RW resulting in twelve different peat:RW media. The RW aggregates used were either fine or coarse textured and absorbent or repellent to water. A soil based medium was used as a control. Bulk volume, bulk density, total porosity, water porosity (WP), and aeration porosity (AP) were determined for all media. Hybrid lily, cvs. `Enchantment' and `Jamboree', growth in these media were compared by measuring the dates of visible bud and anthesis, flower number, leaf number and area, plant height and dry weight of stems, leaves, and flowers. Physical properties of the RW media varied significantly from the soil based medium. Increasing the volume percent RW had a negative linear effect on WP but a positive linear effect on AP for all RW aggregates. Lily growth in the soil based medium was statistically similar to all RW media. The dates of visible bud and anthesis, as well as leaf number and area decreased linearly as the volume percent repellent coarse RW increased.

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Bert T. Swanson and James B. Calkins

Five composted Municipal Solid Waste (MSW) (garbage) products and a composted manure were evaluated as container growing media components on eight woody and herbaceous plants. Plant growth response to the different composts and to the quality of compost used was species-specific. Media UM Manure 100 provided the greatest increase in plant height across all species during the first year. However, only one species, V. lentaga, actually ranked number one in UM Manure 100. J.h. `Blue Chip' and A. tuberosa both grew the tallest in Control I. The remaining five species grew tallest in five different media. Therefore, several amended media can provide increased plant height for specific species; however, the top three media for plant height across all species were: #1 UM Manure 100, #2 Prairieland 50, and #3 Pennington 50. Plant height was the lowest in Recomp 100 media. Pennington 50 provided the greatest increase in plant volume. Media producing the highest plant dry weights across all species were: #1 Prairieland 50, #2 Pennington 50 and #3 UM Manure 50. Plants grown in Recomp 100 had the lowest plant dry weight. Media physical properties such as media drainage and aeration were affected by amendment quality and quantity.

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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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Bruce D. Whitaker

A previous study of lipids from pericarp tissue of tomato fruit ranging from mature-green to red-ripe showed a large increase in total sterols accompanied by dramatic changes in sterol composition and conjugation with ripening. This study was conducted to determine whether similar changes occur in microsomal membranes derived from tomato fruit pericarp. Acylated steryl glycoside (ASG), the predominant steryl lipid, declined during ripening, with increases in steryl glycoside (SG) and free sterol (FS). Only minor changes in fatty acid composition were associated with the drop in ASG. The stigmasterol:sitosterol ratio increased throughout ripening, but much more in Fs than in SG or ASG. The ratio of FS to phospholipid (PL) increased with ripening. However, FS was never greater than 10 percent of the total membrane sterol (TMS), and TMS:PL actually declined over the middle stages of ripening. It is not known why tomato tissues maintain such high levels of ASG and SG, but sterol conjugation is thought to regulate the physical properties of cell membranes.

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Robert H. Stamps and Michael R. Evans

A comparison was made of Philippine coconut coir dust and Canadian spaghnum peat as components of three growing media for greenhouse production of Dieffenbachia maculata `Camille'. The soilless media were prepared using coir or peat in various amounts (by volume) combined with pine bark, vermiculite, and/or perlite (Media A–50% coir/peat: 25% vermiculite: 25% perlite; Media B–40% coir/peat: 30% vermiculite: 30% bark; Media C–50% coir/peat: 50% bark). Chemical and physical properties of the soils were determined at the beginning and the end of the five-month production cycle. Plant root and top growth and grades were determined at the end of the experiment. Initially, saturated media extracts from coir-containing media had elevated K, Cl, and soluble salts levels compared to peat-containing media; however, by the end of the experiment those levels were lower in coir- than in peat-based media. Water-filled pore space and water-holding capacities were generally higher and air-filled pore space lower in coir- than in peat-based media, probably due to differences in particle size distributions. There were no interaction effects on plant growth between growing media and coir versus peat. Plant root and top growth in Media A > Media B > Media C and plant top growth was greater in coir- than in peat-based media. Differences in growth could be due, in part, to differences in media water-holding capacities.