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Mark A. Nash and Franklin A. Pokorny

Component and particle-size effects on shrinkage of two-component potting media were determined. Milled pine bark-sand mixtures were used to determine particle-size effects on shrinkage. Shrinkage curves formed an inverted V with maximum shrinkage at the 1:1 (v/v) ratio. No shrinkage occurred when bark was mixed with bark or sand with sand. Shrinkage increased linearly in the range of 0% to 50% bark and decreased linearly in the range of 50% to 100% bark. Each half of the shrinkage curve was a mirror image of the other half. Shrinkage curves for peat-sand and peat-perlite were similar in form to that of bark-sand media.

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Silvia Bures and Franklin A. Pokorny

An equation for predicting shrinkage in 3-component (ternary) container media was devised. The predictive equation was tested using experimental data obtained from sets of mixtures of milled pine bark, sand, and calcined clay. Each set consisted of 66 different combinations of the experimental components. Actual shrinkage data was correlated with theoretical values calculated from the predictive model. Results of the experiment suggest that shrinkage can be used as a factor with linear programing techniques.

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Silvia Burés, Franklin A. Pokorny, David P. Landau, and Alan M. Ferrenberg

A FORTRAN computer program was developed to simulate packing of spherical particles via a Monte Carlo procedure. Shrinkage in volume upon mixing different particle sizes was studied and simulated results were compared with experimental data. Maximum experimental shrinkage was obtained when the proportion of coarse particles of pine bark and sand mixtures ranged from 50% to 70% of the volume. Experimental shrinkage of a mixture of coarse and fine sand was closely reproduced by means of simulation. Particle size distribution appears to be the most important factor in relation to shrinkage and also in the establishment of relationships between the simulated and the experimental system.

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Robert D. Hagenmaier and Robert A. Baker

The shrinkage rate of `Marsh' grapefruit (Citrus paradisi Macf.), `Ambersweet' hybrid [(C. reticulata Blanco × C. paradisi Macf. × C. reticulata) × C. sinensis (L.) Osb.] and `Valencia' oranges [C. sinensis (L.) Osb.] was increased 50 % to 150% by washing the fruit with rotary brushes, but was not changed by hand-washing the fruit with cellulose sponges. Internal CO2 increased using both washing methods. Waxed fruit obtained from five Florida packinghouses and cleaned with rotary brushes and waxed had shrinkage rates the same as those of nonwashed controls. Thus, controlling the washing process is important to minimize shrinkage of fresh citrus fruit.

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Hiroaki Ito, Takahiro Hayashi, Masaki Hashimoto, Katsuro Miyagawa, Saori Nakamura, Youichi Mizuta, and Susumu Yazawa

applicability test of the established protocol. Flowers were obtained from florists or experimental fields and were used immediately. A protocol for flower processing. Unless otherwise mentioned, ethyl alcohol was used to prevent petal shrinkage in the primary

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Juha Heiskanen

Various irrigation treatments were studied to determine their effects on the water and aeration conditions of peat-based growth media and evaporation from these media. Low-humified sphagnum peat and a mixture of this peat and perlite (in containers) were subjected to three contrasting irrigation treatments in which the container capacity was used as a target water content. The more frequent the reirrigations and the lower the vertical position within containers, the higher the matric potential of the growth medium averaged. Furthermore, the higher the water content of the growth medium, the higher the mean evaporation was from the containers. Within each irrigation treatment, slightly more water (on average) evaporated from the peat than from the peat–perlite mixture. Due to higher water retention and shrinkage during drying, a pure peat growth medium may increase the risk of waterlogging and, hence, O2 deficiency for containerized plants if plants are irrigated frequently to container capacity. To prevent waterlogging and high water loss by evaporation, low-humified sphagnum peat can be irrigated relatively infrequently (especially at low evaporation rates) and thoroughly within a short time (especially at high evaporation rates).

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A. Naor and S. Cohen

The sensitivity of water stress indicators to changing moisture availability, and their variability, determine the number of measurements that should be taken in order to represent properly plant water status in a certain orchard. In the present study we examined the sensitivity and variability of maximum daily trunk shrinkage, midday stem water potential, and daily transpiration rate in their responses to withholding irrigation from field-grown drip-irrigated `Golden delicious' apple trees in a commercial orchard. Irrigation was withheld from the stressed trees for 17 days starting in mid-July, and the control trees were irrigated daily at 100% of the “Class A” pan evaporation rate. The courses of daily transpiration rate, maximum trunk shrinkage, and midday stem water potential before and 10 days after the drying period were similar in the control and the stressed trees. Highly significant differences between the stressed and the control trees in their midday stem water potentials were apparent from the early stages of the stress period. Daily transpiration rate and maximum daily shrinkage were more variable than midday stem water potential, and differences between treatments became significant only after measurements were expressed relative to the initial values before irrigation was witheld. Differences between treatments (as percentages of the values obtained for the control trees) increased after irrigation stopped where these differences were greatest for maximum daily shrinkage, which reached 90%; moderate for stem water potential (60%); and least for daily transpiration rate, for which the differences remained below 20%. Our data show that the choice of a certain water stress indicator should be based on both the sensitivity to changing moisture availability and the degree of variability. Possible reasons for the different sensitivity to moisture availability and the different variability between the water stress indicators under study are discussed.

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Theo J. Blom and Brian D. Piott

High-volume top irrigation (Chapin) was compared to subirrigation (ebb and flow) using 15-cm-diameter (1.56 liter) pot-grown chrysanthemums [Dendranthema ×grandiflorum (Ramat.) Kitamura] with peatwool (50 peatmoss: 50 granulated rockwool) as the growing substrate. Preplant moisture contents (25%, 125%, and 250%, gravimetric) and compaction (0, 20, and 50 g·cm-2) of the peatwool were also studied. Shrinkage of growing substrate was large (>309'6 of pot volume) when peatwool in the pots was not compacted. Compaction reduced shrinkage and produced plants with larger leaves, more fresh weight, and longer stems than without preplant compaction. Drainable pore space, container capacity, and total porosity was not affected by compaction. The higher preplant moisture contents increased drainable pore space but had no effect on plant growth. Chapin-irrigated plants had significantly more fresh weight (+ 24%) at the pea-size bud stage than plants grown in the ebb-and-flow system. The difference in growth was similar at flowering but significant only at P = 0.08. Soluble salts concentration in the peatwool and foliar nutrient contents differed at flowering for the two irrigation systems.

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Silvia Bures and Franklin A. Pokorny

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Benjamin Mullinix and Albert Purvis

Five `Poinsett' cucumbers were selected at random for each treatment in a postharvest storage experiment. Each cucumber was weighed initially, covered by wax “E”, and weighed each day afterwards for 9 days. Percentage loss was computed for each day. Quadratic regression curves were fit for each cucumber and for all in a single analysis. In most cases, variances were not homogeneous among the five cucumbers. Using the regression coefficients for each cucumber, an average of the five was made and appropriate standard errors were computed. Percent loss data was transformed using SQRT. The number of cases where homogeneity of variances were found increased. Mixture of large and small cucumbers by weight tended not to be homogeneous, whereas mixing of cucumbers of similar weights were improved with square-root transformation.