Addition of a polyacrylamide hydrogel to pine bark and pine bark + sand substrates had no effect on total porosity, regardless of incorporation rate. Container capacity was increased with increasing rate of hydrogel in both substrates. Air space in pine bark was slightly increased at the lowest rate but was reduced with higher incorporation rates. Air space in pine bark + sand was reduced with all hydrogel additions. The dry weigh', of hydrogel cubes recovered from both substrates was similar to amounts predicted. This result indicates that blending hydrogel granules into the substrates was uniform and did not contribute to variability in hydrogel studies. After allowing dry hydrogel granules to expand freely in distilled water for 24 hours, hydrogel granules expanded 317 and 372 times their dry weights at the lowest and highest rates, respectively. Reduction of expansion (in water) at higher rates may have been due to physical restriction of expansion. Conversely, recovered hydrogel cubes from substrates watered to drainage (-10% excess) for 6 weeks absorbed 25 to 55 times their dry weight while in the container. Subsequent rehydration of extracted gels in distilled water was greater for hydrogel cubes from the pine bark + sand medium (104 to 130) than in pine bark alone (51 to 88). Because of anomalies in hydraulic conductivity and pressure plate contact, three techniques were used to study unavailable water content in gels expanded in distilled water. Hydrogel cubes placed in direct contact with the pressure plate released ≈95% of their water at pressures ≤ 1.5 MPa. Effectiveness of ployacrylamide gels in coarse-structured substrates is influenced by physical restrictions to expansion in the substrate and hydraulic conductivity between the hydrogel cubes and the surrounding substrate.
W.C. Fonteno and T.E. Bilderback
W. C. Fonteno and E. L. McWilliams
Whole plant net CO2 exchange, light compensation points, and acclimatization were determined for Philodendron scandens Subsp. oxycardium (Schott) Bunt, Epipremnum aureum (Linden & Andre) Bunt (Pothos), Brassaia actinophylla Endl. and Dracaena sanderana Sander before and after 4 and 15 week acclimatization periods at 27 μE m−2 sec−1 (400-700 nm), for 12 hr/day. Philodendron scandens Subsp. oxycardium, E. aureum, B. actinophylla and D. Sanderana exhibited CO2 uptake rates of 0.53, 1.16, 1.18 and 0.50 mg CO2 dm−2hr−1, respectively, at 57 μE m−2 sec−l (3400 lx) after 15 weeks of acclimatization. Each species showed a significant increase in net CO2 uptake during the study period. Dark respiration decreased 63% in P. scandens Subsp. oxycardium, 71% in E. aureum, 53% in B. actinophylla and 64% in D. sanderana during the acclimatization period.
The regression correlation coefficient of CO2 uptake with light intensity increased for each species during the study. At 15 weeks, P. scandens Subsp. oxycardium, E. aureum, B. actinophylla and D. sanderana exhibited r values of .95, .98, .96, and .91, respectively. Light compensation points decreased between week 1 and week 15 as follows: 33 to 7 μE m−2 sec−1 in P. scandens Subsp. oxycardium, 38 to 6 μE m−2 sec−1 in E. aureum, 14 to 4 μE m−2 sec−1 in B. actinophylla and 119 to 15 μE m−2 sec−1 in D. sanderana.
As a result of acclimatization, all species exhibited increases in net CO2 uptake and decreases in dark CO2 evolution concomitantly indicating a reduction in dark respiration. Leaf area increase was negatively correlated with light compensation point. B. actinophylla had the highest leaf area increase with 2.16 dm2, E. aureum and P. scandens Subsp. oxycardium were intermediate with 1.08 and 0.96 dm2, respectively, while D. sanderana, the species with the highest light compensation point exhibited the lowest leaf area increase (0.44 dm2). Philodendron scandens Subsp. oxycardium, E. aureum, B. actinophylla, exhibited similarly rapid rates of acclimatization, while D. sanderana acclimatized much more slowly and had a significantly higher light compensation point.
W. C. Fonteno, D. K. Cassel, and R. A. Larson
Three fundamental different media 3 pine bark (≤ 6mm): 1 sphagnum peat moss:l concrete grade sand; 2 loamy soil: 1 peat moss: 1 perlíte; and a peat-lite mix, (Metro Mix 350) were characterized by available water-holding capacity, bulk density and particle size distribution. All 3 media provided adequate water-holding capacities for container production of ‘Eckespoint C-1 Red’ and ‘Annette Hegg Diva’ poinsettias (Euphorbia pulcherrima Klotzsch ex. Willd.). Total porosity declined and bulk density increased in all media 9 weeks after potting due to shrinkage but there were no additional changes after an additional 4 weeks. Airspace and water buffering capacities did not change during the 13-week period indicating the loss in total porosity resulted in a loss of easily available water. Water release had linear and nonlinear components with respect to moisture tension. Poinsettia root systems appeared to be extensive throughout the growing media; root distributions varied with cultivar and medium.
P.T. Karlovich and W.C. Fonteno
No differences in final height, top fresh weight, top dry weight, or flower number were observed in Chrysanthemum morifolium Ramat. ‘Spice’ grown in 16.5-cm azalea pots when allowed to dry to soil moisture tensions of 5, 10, 20, or 30 kPa between waterings. Differences did occur in these parameters among the 3 tested media. Differences also occurred across all 3 media based on the volume of water remaining in the pot prior to watering. Plants growing in media containing more than 500 ml water just prior to irrigation had increased growth compared to plants in media containing less than 500 ml water. Cubic regression models were used to describe the percentage of moisture in the pot at soil moisture tensions between 0 and 30 kPa. The model may be used to predict container capacity and air space for most container sizes.
W. C. Fonteno and R. A. Larson
Extended long days or interrupted night photoperiods increased leaf number and top fresh weight, and decreased tuber formation compared with short days with 2 cultivars of the “NonStop” series of tuberous begonia (Begonia X tuberhybrida Voss). Short days increased tuber size and fresh weight and reduced top fresh weight of both cultivars. ‘Double Red’ showed greater leaf number, top fresh weight, tuber fresh weight, and tuber size at 22°C than at 26°, while ‘Double Orange’ showed only greater top fresh weight at 22°. Flowering was enhanced in both cultivars under long days.
W. Garrett Owen, Brian E. Jackson, Brian E. Whipker, and William C. Fonteno
Processed pine (Pinus sp.) wood has been investigated as a component in horticultural substrates (greenhouse and nursery) for many years. Specifically, pine wood chips (PWC) have been uniquely engineered/processed into a nonfiberous blockular particle size, suitable for use as a substrate aggregate. The purpose of this research was to determine if paclobutrazol drench efficacy is affected by PWC used as a substitute for perlite in a peat-based substrate. Paclobutrazol drench applications of 0, 1, 2, and 4 mg/pot were applied to ‘Pacino Gold’ sunflower (Helianthus annuus); 0.0, 0.25, 0.50, and 1.0 mg/pot to ‘Anemone Safari Yellow’ marigold (Tagetes patula); and 0.0, 0.125, 0.25, and 0.50 mg/pot to ‘Variegata’ plectranthus (Plectranthus ciliates) grown in sphagnum peat-based substrates containing 10%, 20%, or 30% (by volume) perlite or PWC. Efficacy of paclobutrazol drenches for controlling growth of all three species was unaffected by substrate composition. We concluded that substituting PWC for perlite as an aggregate in peat-based substrates should not reduce paclobutrazol drench efficacy, variability in PWC products indicates that efficacy should be tested before large-scale use. The variability results from wood components not being engineered and processed the same across manufacturers, meaning that they are often incapable of improving/influencing the physical and chemical behavior of a substrate similarly.
W. Garrett Owen, Brian E. Jackson, Brian E. Whipker, and William C. Fonteno
Processed pine wood (Pinus sp.) has been investigated as a component in greenhouse and nursery substrates for many years. Specifically, pine wood chips (PWC) have been uniquely engineered/processed into a nonfiberous blockular particle size, suitable for use as a substrate aggregate. In container substrates, nitrogen (N) tie-up during crop production is of concern when substrates contain components with high carbon (C):N ratios, like that of PWC that are made from fresh pine wood. The objective of this research was to compare the N requirements of plants grown in sphagnum peat–based substrates amended with perlite or PWC. Fertility concentrations of 100, 200, or 300 mg·L−1 N were applied to ‘Profusion Orange’ zinnia (Zinnia ×hybrida) and ‘Moonsong Deep Orange’ marigold (Tagetes erecta) grown in sphagnum peat–based substrates containing 10%, 20%, or 30% (by volume) perlite or PWC. Zinnia plant substrate solution electrical conductivity (EC) was not influenced by percentage of perlite or PWC. Perlite-amended substrates fertilized with 200 mg·L−1 N for growing zinnia, maintained a constant EC within optimal levels of 1.0 to 2.6 mS·cm−1 from 14 to 42 days after planting (DAP), and then EC increased at 49 DAP. In substrates fertilized with 100 and 300 mg·L−1 N, EC levels steadily declined and then increased, respectively. Zinnia plants grown in PWC-amended substrates fertilized with 200 mg·L−1 N maintained a constant EC within the optimal range from 14 to 49 DAP. Marigold substrate solution EC was only influenced by N concentration and followed a similar response to zinnia substrate solution EC. Zinnia and marigold substrate solution pH was influenced by N concentration and generally decreased with increasing N concentration. Plant growth and shoot dry weight were similar when fertilized with 100 and 200 mg·L−1 N. According to this study, plants grown in PWC-amended substrates fertilized with 100 to 200 mg·L−1 N can maintain adequate substrate solution pH and EC levels and sustain plant growth with no additional N supplements. Pine wood chips are engineered and processed to specific sizes and shapes to be functional as aggregates in a container substrate. Not all wood components are designed or capable of improving/influencing the physical and chemical behavior of a substrate the same. On the basis of the variability of many wood components being developed and researched, it is suggested that any and all substrate wood components not be considered the same and be tested/trialed before large-scale use.
Kenneth M. Tilt, T.E. Bilderback, and W.C. Fonteno
Composted hardwood bark and aged pine bark were combined to produce two media with different particle size fractions. Media were combined with 3.8-, 5.7-, and 11.4-liter containers to produce six air and water capacities. Rooted cuttings of Ilex × ‘Nellie R. Stevens’ Van Lennep holly, × Cupressocyparis leylandii Jacks and Dall. ‘Ηaggerston Grey’ leyland cypress and Rhododendron × sp. ‘Sunglow’ azalea were potted in the resulting media–container combinations to determine the effects of particle size distribution, moisture and air content, and volume of containers on plant growth. Manipulating the particle size decreased the water held by ≈9%, but increased air space by ≈8% between the control and the coarse medium. The control medium yielded greatest top dry weight for all three species. Root dry weight and root ball volume were similar in coarse and control medium. Plant growth also was related to container size. A 2-fold increase in top dry weight occurred as container volume of the medium increased from 3.8 to 11.4 liters. Increasing container water content had a significant effect on top dry weight of all three species. Aeration was not as limiting to root growth as water content was to top growth.
T. E. Bilderback, W. C. Fonteno, and D. R. Johnson
Equal volumes of peanut hulls, pine bark, and sphagnum peatmoss were combined into 5 media. Particle size distribution, total porosity, air space, easily available water, water buffering capacity, and bulk density were determined for each medium. Top dry weight, root dry weight, and percent growth of Rhododendron indicum (L.) Sweet cv. George L. Taber were measured 14 weeks after potting in 1-liter containers. Peanut hulls increased particle size, total porosity, and air space, and decreased easily available water, water buffering capacity, and bulk density of media. Peatmoss generally reduced total porosity and air space and increased easily available water, water buffering capacity, and bulk density regardless of other component combinations. Top dry weight, root dry weight, and percent growth were greater in peanut hull-containing media. Addition of peatmoss to the container media tended to produce less growth.
W. Garrett Owen, Brian E. Jackson, William C. Fonteno, and Brian E. Whipker
Processed loblolly pine (Pinus taeda) wood has been investigated as a component in greenhouse and nursery substrates for many years. Specifically, pine wood chips (PWCs) have been uniquely engineered/processed into a nonfibrous blockular particle size suitable for use as a substrate aggregate. The objective of this research was to compare the dolomitic limestone requirements of plants grown in peat-based substrates amended with perlite or PWC. In a growth trial with ‘Mildred Yellow’ chrysanthemum (Chrysanthemum ×morifolium), peat-based substrates were amended to contain 0%, 10%, 20%, 30%, 40%, or 50% (by volume) perlite or PWC for a total of 11 substrates. Substrates were amended with dolomitic limestone at rates of 0, 3, 6, 9, or 12 lb/yard3, for a total of 55 substrate treatments. Results indicate that pH of substrates amended with ≥30% perlite or PWC need to be adjusted to similar rates of 9 to 12 lb/yard3 dolomitic limestone to produce similar-quality chrysanthemum plants. In a repeated study, ‘Moonsong Deep Orange’ african marigold (Tagetes erecta) plants were grown in the same substrates previously formulated (with the exclusion of the 50% ratio) and amended with dolomitic limestone at rates of 0, 3, 6, 9, 12, or 15 lb/yard3, for a total of 54 substrate treatments. Results indicate a similar dolomitic limestone rate of 15 lb/yard3 is required to adjust substrate pH of 100% peatmoss and peat-based substrates amended with 10% to 40% perlite or PWC aggregates to the recommended pH range for african marigold and to produce visually similar plants. The specific particle shape and surface characteristics of the engineered PWC may not be similar to other wood products (fiber) currently commercialized in the greenhouse industry, therefore the lime requirements and resulting substrate pH may not be similar for those materials.