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Due to uncertainties of future supplies of pine bark (PB) and peatmoss, ground Pinus taeda logs [pine chips (PC)] were compared to ground PB as a potential container substrate for japanese holly (Ilex crenata Thunb. `Chesapeake'), azalea (Rhododendron obtusum Planch. `Karen'), and marigold (Tagetes erecta Big. `Inca Gold'). Plants were potted in 2.8-L plastic containers 8 Apr. 2004 with either 100% PC, 100% PB, or 75% PC:25%PB (v/v), and glasshouse grown 8 weeks for marigold and 13 weeks for holly and azalea. Plant dry weights were higher for marigold grown in 100% PB compared to 100% PC but not different from plants grown in 75% PC:25% PB. Plant dry weights of azalea were higher in 100% pine bark than both substrates containing chips. There was no difference in shoot dry weight for japanese holly between the three substrates. Root dry weight was higher for 75% PC:25% PB than for 100% PB, but root weight of 100% PB and 100% PC was the same. The percent air space for the PC was higher than the PB substrate but container capacity and available water was not different for the three substrates. Substrate solution electrical conductivity (EC) for PC, was lower than that of PB, possibly due to greater leaching with the more porous PC and nutrient retention by the PC. These factors could account for the cases where larger plants developed with the PB substrate. Nutrient analysis of the substrate solution indicated that there are no toxic nutrient levels associated with PC. The pH of PC is also acceptable for plant culture. As well, there was no apparent shrinkage due to decomposition during the course of this short-term experiment. Pine chips, therefore, offer potential as a container substrate for greenhouse and nursery crops.

Many industrial and agricultural wastes have been evaluated for use as alternative container substrate components. Recently, a new material produced from ground pine logs (Pinus taeda L.) has been utilized as a substitute for peat moss and pine bark (PB). On 17 Aug. 2005, japanese holly (Ilex crenata `Compacta' Thunb.) plants were potted in milled PB (Pinus taeda L.) and debarked ground pine chips (PC). Pine chips were ground with a hammermill to pass through a 6.35-mm screen. Osmocote Plus 15–9–12 (15N–4P–10K) was incorporated in both PB and PC substrates at the rates of 3.5, 5.9, 8.3, and 10.6 kg·m^-3. Plants were greenhouse grown until 22 Nov. 2005. Substrate solution nutrient content and pH were determined for all treatments in each substrate. Shoots were dried, weighted, and tissue analyzed for N, P, K, Ca, Mg, S, Fe, Cu, Mn, and Zn. Shoot weights were higher in plants grown in PB than PC at the 3.5 and 5.9 kg·m^-3 fertilizer rates. At the 8.3 kg·m^-3 rate, shoot dry weight was about the same for each substrate, but at the 10.6 kg·m^-3 rate, growth was higher for plants grown in PC than in PB. Substrate EC increased with increasing fertilizer rates and with the exception of Cu, was higher in PB substrates at all fertilizer rates. Plant tissue levels generally increased as fertilizer rate increased in both substrates but were higher in plants grown in PB than PC with the exception of Cu. Therefore, higher rates of fertilizer are required to produce optimal plant growth in PC compared to PB.

Posttransplant root growth is critical for landscape plant establishment. The Horhizotron provides a way to easily measure root growth in a wide range of rhizosphere conditions. Mountain laurel (Kalmia latifolia L.) plants were removed from their containers and planted in Horhizotrons in a greenhouse in Auburn, Ala., and outdoors in Blacksburg, Va. Each Horhizotron contained four glass quadrants extending away from the root ball, and each quadrant within a Horhizotron was filled with a different substrate (treatment): 1) 100% pine bark (Pinus taeda L., PB), 2) 100% soil, 3) a mixture of 50 PB: 50 soil (by volume), or 4) 100% soil along the bottom of the quadrant to a depth of 10 cm (4 inches) and 100% PB layered 10 cm (4 inches) deep on top of the soil. Root growth along the glass panes of each quadrant was measured biweekly in Auburn and weekly in Blacksburg. Roots were longer in all treatments containing pine bark than in 100% soil. When pine bark was layered on top of soil, roots grew into the pine bark but did not grow into the soil. Results suggest that amending soil backfill with pine bark can increase posttransplant root growth of container-grown mountain laurel.

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.

Substrates of container-grown plants are commonly preplant amended with sulfated micronutrients to supply micronutrients. However, the cause for the increased growth may be due to micronutrient addition or other factors such as S addition or substrate acidification. Container-grown pin oak (Quercus palustris Müench) and japanese maple (Acer palmatum Thunb.) seedlings were grown in a 100% pine bark substrate and amended (or not) with one of the following treatments: control (no amendment), Micromax, K₂SO₄, H₂SO₄, HCl, chelated micronutrients, elemental S, or CaSO₄. After 11 weeks, dry weights of plants in all treatments supplying S were higher than plants receiving no S. Dry weights of plants in all experiments receiving the chelate treatment were not higher than dry weights for control plants. These data indicate that S, not micronutrient application, is a primary cause of increased growth from the addition of sulfated micronutrients. However, it was demonstrated that there are conditions such as higher substrate solution pH (4.1 vs. 5.4), where Micromax may prove advantageous over sulfur alone since it would supply micronutrients as well as S.

Sulfur (S) is essential to the growth of higher plants; however, research on S fertilizer requirements for container-grown nursery tree species has not been established. The purpose of this study was to determine the substrate solution S concentration that maximizes the growth of container-grown pin oak (Quercus palustris Münchh) (pin oak–K₂SO₄ experiment) and japanese maple (Acer palmatum Thunb.) (japanese maple–K₂SO₄ experiment) in a pine bark (PB) substrate. Both species were fertilized with solutions supplying a range of S concentrations (0, 1, 2, 5, 10, 20, 40, or 80 mg·L^–1) using K₂SO₄. Regression analysis revealed that dry weights of both species were near maximum at the predicted application concentration of 30 mg·L^–1 S, which corresponded to about 15 and 7 mg·L^–1 S in substrate solution for pin oak and japanese maple, respectively. In a Micromax, FeSO₄, lime experiment, S was supplied to pin oak via a preplant micronutrient sulfate fertilizer or FeSO₄ in limed or unlimed PB. When the PB pH was relatively low (4.5, unlimed), FeSO₄ and the preplant micronutrient fertilizer were effective in supplying ample S. However, when the PB pH was relatively high (6.1, limed), the preplant micronutrient fertilizer with micronutrients in a sulfate form was more effective in supplying S and micronutrients than FeSO₄.

A pine tree substrate (PTS), produced by grinding loblolly pine trees (Pinus taeda), offers potential as a viable container substrate for greenhouse crops, but a better understanding of the fertilizer requirements for plant growth in PTS is needed. The purpose of this research was to determine the comparative fertilizer requirements for chrysanthemum (Chrysanthemum ×grandiflora ‘Baton Rouge’) grown in PTS or a commercial peat-lite (PL) substrate. The PTS was prepared by grinding coarse (1-inch × 1-inch × 0.5-inch) pine chips from debarked loblolly pine logs in a hammer mill fitted with 3/16-inch screen. The PL substrate composed of 45% peat, 15% perlite, 15% vermiculite, and 25% bark was used for comparative purposes. Rooted chrysanthemum cuttings were potted in each of the substrates on 15 Oct. 2005 and 12 Apr. 2006 and were glasshouse grown. Plants were fertilized with varying rates of a 20N–4.4P–16.6K-soluble fertilizer ranging from 50 to 400 mg·L⁻¹ nitrogen (N) with each irrigation. Plant dry weights and extractable substrate nutrient levels were determined. In 2005 and 2006, it required about 100 mg·L⁻¹ N more fertilizer for PTS compared to PL to obtain comparable growth. At any particular fertilizer level, substrate electrical conductivity and nutrient levels were higher for PL compared to PTS accounting for the higher fertilizer requirements for PTS. Possible reasons for the lower substrate nutrients levels with PTS are increased nutrient leaching in PTS due to PTS being more porous and having a lower cation exchange capacity than PL, and increased microbial immobilization of N in PTS compared to PL. This research demonstrates that PTS can be used to grow a traditional greenhouse crop if attention is given to fertilizer requirements.

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.