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Brian E. Jackson, Robert D. Wright, and Michael C. Barnes

The use of freshly harvested and processed pine trees as a container substrate for greenhouse and nursery crop production is a relatively new concept, and fundamental knowledge of the construction of a pine tree substrate (PTS) for optimal physical properties is insufficient. Therefore, this research was conducted to determine the influence of mixing PTSs produced with different wood particle sizes and adding other amendments to PTS on substrate physical properties and plant growth compared with traditional substrates. Coarse pine wood chips produced from 15-year-old loblolly pine trees (Pinus taeda L.) were ground in a hammermill fitted with either a 4.76-mm screen or with no screen (PTS-NS) allowing a fine and a coarse particle PTS to be produced. Increasing proportions of the finer (4.76-mm) PTS to the coarser PTS (PTS-NS) resulted in increased container capacity (CC) and shoot growth of ‘Inca Gold’ marigold (Tagetes erecta L.). In another study, PTSs were manufactured in a hammermill fitted with different screen sizes: 4.76, 6.35, 9.54, or 15.8 mm as well as PTS-NS. After being hammermilled, each of the five PTSs was then amended (by mixing) with 10% sand (PTS-S), 25% peatmoss (PTS-PM), or left unamended. Pine tree substrates were also produced by adding 25% aged pine bark (PB) to pine wood chips before being ground in a hammermill with each of the five screen sizes mentioned (PTS-HPB). These five substrates were used unamended as well as amended with 10% sand after grinding (PTS-HPBS). Control treatments included peat-lite (PL) and 100% aged PB for a total of 27 substrates evaluated in this study. Container capacity and marigold growth increased as screen size decreased and with the additions of peatmoss (PTS-PM) or hammering with PB (PTS-HPB) to PTS. Container capacity for all substrates amended with peatmoss or PB was within the recommended range of 45% to 65% for container substrates, but only with the more finely ground PTS-4.76-mm resulted in marigold growth comparable to PL and PB. However, when the PTS-NS was amended by mixing in 25% peat or hammering with 25% PB, growth of marigold was equal to plants grown in PL or PB. In a third study, hammering PTS-NS with 25% PB followed by the addition of 10% sand increased dry weight of both azalea (Rhododendron ×hybrida ‘Girard Pleasant White’) and spirea (Spiraea nipponica Maxim. ‘Snowmound’) resulting in growth equal to plants grown in 100% PB. This work shows that amending coarsely ground PTS with finer particle PTS or with other materials (peatmoss, aged PB, or sand) can result in a substrate with comparable physical properties such as CC and plant growth compared with 100% PL or PB.

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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.

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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.

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Brian A. Kahn, John P. Damicone, Kenneth E. Jackson, James E. Motes, and Mark E. Payton

Nematodes (Meloidogyne sp.) are a potential problem when paprika peppers (Capsicum annuum L.) are grown in fields historically planted to peanuts (Arachis hypogaea L.). Nine nematicide treatments were evaluated over 3 years in field experiments on paprika pepper. Materials tested included the chitin nematicide ClandoSan and six chemicals: fosthiazate, carbofuran, aldicarb, oxamyl, fenamiphos, and dichloropropene. Stands at harvest were increased relative to the control by ClandoSan in 2 of 3 years. Other horticultural effects (plant dry mass and fruit yield) were minimal for all nine nematicide treatments. No one nematicide treatment consistently reduced nematode counts at harvest relative to the control. Nematode counts at harvest were greater in plots treated with ClandoSan than in plots treated with any other material in 2 of 3 years. Nematicide treatments were not cost effective under the conditions of these studies.

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Brian A. Kahn, John P. Damicone, Kenneth E. Jackson, James E. Motes, and Mark E. Payton

Nine nematicide treatments were evaluated from 1993 through 1995 in field experiments on paprika pepper (Capsicum annuum L.). Materials tested included a chitinurea soil amendment and six chemicals: fosthiazate, carbofuran, aldicarb, oxamyl, fenamiphos, and 1,3-dichloropropene (1,3-D). Stands at harvest were increased relative to the control by chitin-urea, fosthiazate, and 1,3-D, but only fosthiazate increased marketable fruit yield relative to the control. Aldicarb reduced preharvest nematode populations relative to the control, but aldicarb did not result in a significant fruit yield increase. Chitin-urea was the only treatment to produce a net increase in nematode counts from preplant to preharvest in all three years. Although fosthiazate was promising, nematicide treatments were of limited benefit under the conditions of these studies. Chemical names used: (RS)-S-sec-butyl O-ethyl 2-oxo-1,3-thiazolidin-3-ylphosphonothioate (fosthiazate); 2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate (carbofuran); 2-methyl-2-(methylthio)propionaldehyde O-(methylcarbamoyl)oxime (aldicarb); methyl N′N′ -dimethyl-N-[(methylcarbamoyl)oxy]-1-thiooxamimidate (oxamyl); ethyl 3-methyl-4-(methylthio)phenyl(1-methylethyl) phosphoramidate (fenamiphos).

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James E. Altland, James S. Owen Jr., Brian E. Jackson, and Jeb S. Fields

Pine bark is the primary constituent of nursery container media (i.e., soilless substrate) in the eastern United States. Pine bark physical and hydraulic properties vary depending on the supplier due to source (e.g., lumber mill type) or methods of additional processing or aging. Pine bark can be processed via hammer milling or grinding before or after being aged from ≤1 month (fresh) to ≥6 month (aged). Additionally, bark is commonly amended with sand to alter physical properties and increase bulk density (Db). Information is limited on physical or hydraulic differences of bark between varying sources or the effect of sand amendments. Pine bark physical and hydraulic properties from six commercial sources were compared as a function of age and amendment with sand. Aging bark, alone, had little effect on total porosity (TP), which remained at ≈80.5% (by volume). However, aging pine bark from ≤1 to ≥6 months shifted particle size from the coarse (>2 mm) to fine fraction (<0.5 mm), which increased container capacity (CC) 21.4% and decreased air space (AS) by 17.2% (by volume) regardless of source. The addition of sand to the substrate had a similar effect on particle size distribution to that of aging, increasing CC and Db while decreasing AS. Total porosity decreased with the addition of sand. The magnitude of change in TP, AS, CC, and Db from a nonamended pine bark substrate was greater with fine vs. coarse sand and varied by bark source. When comparing hydrological properties across three pine bark sources, readily available water content was unaffected; however, moisture characteristic curves (MCC) differed due to particle size distribution affecting the residual water content and subsequent shift from gravitational to either capillary or hygroscopic water. Similarly, hydraulic conductivity (i.e., ability to transfer water within the container) decreased with increasing particle size.

Open access

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.

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Brian E. Jackson, Joe M. Kemble, Amy N. Wright, and Jeff L. Sibley

Tomatoes are the most abundantly produced greenhouse vegetable crop in the United States. The use of compost substrates has increased in recent years for the greenhouse production of many vegetables, bedding plants, and nursery crops. `Blitz' tomatoes were grown during the spring and fall growing seasons in 2004 in six substrate blends of pine bark (PB), a traditional production substrate in the Southeastern U.S., and cotton gin compost (CGC), an agricultural by-product, to assess the potential use of CGC as a viable replacement for PB for the production of greenhouse tomatoes. Treatments ranged from 100% PB to 100% CGC. During both growing seasons, plants grown in substrates containing CGC produced similar total, marketable, and cull yields compared to plants grown in 100% PB. Substrates containing 40% or more CGC had significantly higher EC levels both initially and throughout both growing seasons than did 20% CGC and 100% PB blends. Initial and final pH of all substrates was similar during both studies and remained within recommended ranges for greenhouse tomato production. Water-holding capacity increased as the percent CGC increased in each substrate blend, indicating the need for less irrigation volume for substrates containing CGC compared to the 100% PB control. Results indicate that CGC can be used as an amendment to or replacement for PB in greenhouse tomato production.

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Brian E. Jackson, Robert D. Wright, Jake F. Browder, J. Roger Harris, and Alex X. Niemiera

Recent interest in the use of wood substrates in horticulture crop production has justified the need for determining fertilizer requirements in these substrates compared with traditional pine bark (PB) and peatmoss substrates. The objective was to determine the response of japanese holly (Ilex crenata Thunb. ‘Compacta’) and azalea (Rhododendron obtusum Planck. ‘Delaware Valley’) grown in a pine tree substrate (PTS) (trade name WoodGro™) or milled PB to fertilizer rate. Pine tree substrate is produced from freshly harvested loblolly pine trees (Pinus taeda L.) that are delimbed, chipped, and ground in a hammer mill to a desired particle size. Japanese holly plants were grown in 2.8-L containers in the fall of 2005 and again in the spring of 2007 with the addition of azalea. Plants grown in PTS or PB were fertilized by incorporating Osmocote Plus fertilizer (15N–3.9P–10K) at rates of 3.5, 5.9, 8.3 or 10.6 kg·m−3 for japanese holly and 1.2, 3.5, 5.9, or 8.3 kg·m−3 for azalea. After 3 months, shoot dry weights were determined for japanese holly and azalea. Japanese holly root dry weights were determined for both experiments, and substrate CO2 efflux (μmol CO2 m−2·s−1) was measured on the treatments at the end of the experiment using a LI-6400 soil CO2 flux chamber. In 2005, japanese holly shoot dry weights of PTS-grown plants were comparable to plants grown in PB at the 8.3 kg·m−3 fertility rate, and shoot dry weights of PTS-grown plants were higher than PB at the 10.6 kg·m−3 rate. In 2007, japanese holly and azalea shoot dry weights of PTS-grown plants were comparable to PB plants at the 5.9 kg·m−3 fertilizer rate. Both japanese holly and azalea achieved shoot growth in PTS comparable to shoot growth in PB with ≈2.4 kg·m−3 additional fertilizer for PTS. Substrate CO2 efflux rates were higher in PTS compared with PB indicating higher microbial activity, thereby increasing the potential for nutrient immobilization in PTS.

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Robert D. Wright, Brian E. Jackson, Michael C. Barnes, and Jake F. Browder

The objective of this study was to evaluate the landscape performance of annual bedding plants grown in a ground pine tree substrate (PTS) produced from loblolly pine trees (Pinus taeda) or in ground pine bark (PB) when transplanted into the landscape and grown at three different fertilizer rates. Begonia (Begonia ×semperflorens-cultorum) ‘Cocktail Vodka’, coleus (Solenostemen scutellarioides) ‘Kingswood Torch’, impatiens (Impatiens walleriana) ‘Dazzler White’, marigold (Tagetes erecta) ‘Bonanza Yellow’, petunia (Petunia ×hybrid) ‘Wave Purple’, salvia (Salvia splendens) ‘Red Hot Sally’, and vinca (Catharanthus roseus) ‘Cooler Pink’ were evaluated in 2005, and begonia ‘Cocktail Whiskey’, marigold ‘Inca Gold’, salvia ‘Red Hot Sally’, and vinca ‘Cooler Pink’ were evaluated in 2006 and 2007. Landscape fertilizer rates were 1 lb/1000 ft2 nitrogen (N) in 2005 and 0, 1, and 2 lb/1000 ft2 N in 2006 and 2007. Visual observations throughout each year indicated that all species, whether grown in PTS or PB, had comparable foliage quality in the landscape trial beds during the growing period. With few exceptions, dry weight and plant size for all species increased with increasing fertilizer additions, regardless of the substrate in which the plants were grown. For the unfertilized treatment, when comparing plant dry weight between PB and PTS for each species and for each year (eight comparisons), PTS-grown plant dry weight was less than PB-grown plants in three out of the eight comparisons. However, there were fewer differences in plant dry weight between PTS- and PB-grown plants when fertilizer was applied (PTS-grown plants were smaller than PB-grown plants in only 2 of the 16 comparisons: four species, two fertilizer rates, and 2 years), indicating that N immobilization may be somewhat of an issue, but not to the extent expected. Therefore, the utilization of PTS as a substrate for the production of landscape annuals may be acceptable in the context of landscape performance.