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, K 2 SO 4 , H 2 SO 4 , HCl, chelated micronutrients, elemental S, or CaSO 4 . 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.

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.

Containerized seedlings of eastern redcedar (Juniperus virginiana L.) were fertilized weekly for 175 days with a solution containing 50 ppm P, 150 ppm K, and either 0, 5, 10, 20, 40, 80, 160, 320, or 640 ppm N. Plant height, stem diameter, and shoot and root dry weights increased asymptotically with applied N; 640 ppm N diminished response. Growth after 175 (height, stem diameter) and 180 (shoot and root dry weights) days was optimal (90% of maximum) at N concentrations of 115, 155, 230, and 105 ppm, respectively; 1.5% foliar N optimized height growth. Foliar concentrations of N, P, and K increased in treated plants over the duration of the experiment, while Ca, Mg, and Mn decreased or remained constant. Starch concentration of fertilized plants decreased sharply after initiation of the experiment, but controls showed little change during the first 120 days. Sucrose concentration remained constant over the summer but increased sharply in late fall. At 180 days, foliar concentrations of starch, sucrose, hexose, N, P, K, and B increased asymptotically with applied N; concentrations of Ca, Mg, and Mn decreased.

Stem cuttings of Blue Rug juniper (Juniperus horizontalis Moench `Wiltonii'), `Hino-Crimson' azalea [ Rhododendron (Lindl.) P1anch `Hino-Crimson'], and `Helleri' holly (Ilex crenata Thunb. `Helleri') were propagated in 1 peat: 1 perlite (v/v) at one of five moisture levels based on medium dry weight (125%, 250%, 375%, 500%, or 625%). Cutting survival and percentage of rooted cuttings were highest at the highest medium moisture level in all three species. Incidence of cutting basal rot was not directly related to medium moisture level, but more to the growth stage of the stock plant. Midday xylem water potential (ψ) of cuttings for each species was highest in the wettest propagation medium and lowest in the driest medium. During propagation, stem cutting ψ below - 2.0 MPa occurred even in the wettest medium tested, and frequently reached - 4.0 MPa in cuttings in the driest treatment (125%). Basal water uptake by cuttings was highest in the wettest medium moisture level. Water uptake was highest during the first few days after insertion, and thereafter decreased until root emergence.

Eastern redcedar (Juniperus virginiana L.) seedlings were grown in 1986 through 1988 in pine bark container media with various levels of dolomitic limestone and micronutrients. Supplemental micronutrients reduced shoot growth, especially in the absence of limestone, and root growth was greatest when neither limestone nor micronutrients were added. Including at least 3.0 kg limestone/m3 in the medium was beneficial, not only as a source of nutrients, but also as a buffer against potentially toxic effects of excess micronutrients.

We determined the influence of moisture stress conditioning (MSC) (exposing plants to four nonlethal dry-down cycles) on gas exchange and water loss of Salvia splendens F. Sellow `Bonfire'. During day 1 following final irrigation, no differences in leaf water potentials (ψ L ) were observed due to MSC. However, MSC plants had lower midday net photosynthesis (Pn), transpiration (E), and leaf conductance (g L ) than controls. Stomatal inhibition of photosynthesis (SI) of MSC plants was greater than that of controls. Further, the lack of differences in mesophyll resistance to CO 2 (r m due to MSC indicate gas exchange differences during day 1 were stomatal in nature. During day 2, MSC plants exhibited greater Pn, E, and g L , while SI and r m were greater for controls. MSC plants maintained positive Pn rates and .turgor and lower ψ L than control plants during day 2. Higher water-use efficiency estimates were observed for MSC plants than for controls.

The influence of K nutrition (25, 75, 150, 300, 450, and 600 mg K/liter) and moisture stress conditioning (MSC) (exposing plants to four sublethal dry-down cycles) on leaf water relations, evapotranspiration, growth, and nutrient content was determined for salvia (Salvia splendens F. Sellow `Bonfire'). Potassium concentration and MSC had an interactive influence on osmotic potential at full (π 100 ) and zero (π 0 ) turgor. Differences in osmotic potential between MSC and non-MSC plants for π 100 and π 0 increased with increasing K concentration. Increasing K concentration and MSC resulted in active osmotic adjustment and, consequently, increased cellular turgor potentials. Foliar K content increased with increasing K concentration and MSC. High K concentrations and MSC both reduced plant evapotranspiration on a per-plant and per-unit-leaf-area basis. Greatest shoot dry weight occurred for plants grown with 300 mg K/liter and non-MSC. Total leaf area increased with increasing K concentration, but MSC had little effect.

Accumulation of biomass and nutrients was examined in a chronosequence of fraser-fir [ Abies fraseri (Pursh) Poir.] Christmas trees. Estimated above-ground biomass of fraser-fir (2.4 to 2.7 m tall, 4444 trees/ha) after 7 years in the field was 40 t·ha -1 , including foliage at 17 t·ha -1 . At harvest, trees of this size removed 499 kg N, 33 kg P, 156 kg K, 160 kg Ca, and 26 kg Mg/ha. Foliage made up 46% and 42% of the total dry weight for 1.5- and 2.6-m trees, respectively. Forty-three percent to 63% of the above-ground nutrient content, depending on the element, was in foliage.

Pine bark cation exchange capacity (CEC) (by Ba/Mg exchange on four particle size fractions) increased regularly from 38 to 98 meq/100 g between pH 4 and 7. Decreasing particle size from <2.38 to <0.05 mm did not result in the expected large increases in bark CEC. The Ba/Mg CEC of unsieved bark samples was less than that determined by the weighted average of component size fractions. Monovalent/monovalent-determined CEC was higher than Ba/Mg, indicating that a number of differing charge-specific sites are involved. The pH-dependent CEC increase between pH 4 and 7 was greater for divalent exchange than for monovalent. Ammonium/K CEC was higher than K/ NH 4 CEC, probably due to enhanced NH 4 adsorption by carboxyl groups. Infrared analysis of pine bark revealed that surface functional group composition is similar to soil organic matter. The accurate measurement of CEC in pine bark is complicated by solution pH and ionic strength, as well as by the cations employed for exchange.

Abstract This study was conducted to determine the availability of N from urea applied to a pine bark container medium. Results showed that negligible amounts of urea are adsorbed to a pine bark medium compared to NH 4 -N. However, 71% of the urea applied was hydrolyzed to NH 4 within 24 hr and 95% within 40 hr. The rapid hydrolysis would allow N from urea to be available for plant uptake or adsorption to bark soon after application, making urea an acceptable source of N for a pine bark medium.

Abstract Nitrification in a pine bark medium in response to a range of applied NH 4 -N levels (25, 100, and 200 ppm) was studied. Medium solution NH 4 -N concentrations at the 25 ppm N treatment decreased from 30 ppm at day 1 to 0 ppm at day 40. Ammoniacal-N concentration values decreased from 64 to 6 ppm and from 105 to 20 ppm for the 100- and 200-ppm N treatments, respectively, by day 60. Rapid increases in medium solution NO 3 -N concentrations coincided with these NH 4 -N decreases, resulting in low medium solution NH 4 -N:NO 3 -N ratios. During the periods of NO 3 -N increase, medium solution pH decreased 0.3, 0.7, and 1.3 units for the 25-, 100-, and 200-ppm N treatments, respectively. Similarly treated bark without plants was used to determine a NO 3 -N accumulation rate (NAR). NAR data indicated that the NH 4 -N supply of the 100- and 200-ppm N treatments exceeded the oxidative capacity of nitrifiers during a 96-hr period.

Abstract The response of cape primrose ( Streptocarpus ) plants to external N application is dependent on growth media only in terms of response magnitude. A 2.0% to 2.9% tissue N level in either sand or bark media maximized shoot dry weight, the number of potential flowers, and the quantity and quality of plantlets regenerated during subsequent asexual propagation. In sand, 2.9% tissue N was below the level required for maximum leaf elongation and resulted in a desirable restriction of the primary leaf (phyllomorph). Tissue N levels that either exceeded or lagged behind the optima were often detrimental to plant aesthetics, and wasteful where luxuriant tissue levels did not affect the measured characteristics.

Abstract Pine bark-filled containers were subjected to 10°, 20°, 30°, or 40°C for 24 days and fertilized periodically with 210 ml of a solution containing 100 ppm NH 4 -N. Every 6 days, medium solutions were tested for NH 4 -N and NO 3 -N concentrations and a NO 3 -N accumulation rate (NAR) was determined. Medium solution NH 4 -N concentrations were lower at 20° and 30° than at 10° and 40°, while those at 40° were considerably greater than at other temperatures and increased over time. In general, medium solution NO 3 -N concentrations at 10°, 20°, and 30° were comparable and higher than at 40°. Over time, the general order of NAR was 20° = 30° > 10° > 40°.

Ilex crenata ‘Helleri’ was greenhouse-grown in sand culture for 8 weeks at 4 levels of N, P and K in a factorial arrangement. Nitrogen and K levels were maintained at 0, 25, 75, and 200 ppm and P at 0, 5, 15, and 40 ppm in the irrigation water. The lowest level of each nutrient required for optimal growth was 75 ppm N, 5-15 ppm P and 25 ppm K. When levels of P were maintained at 40 ppm, then 200 ppm K was required for maximum growth. The same trend occurred for N and P in that higher levels of N were required to promote maximum growth when P levels were at 40 rather than 15 ppm.

The effect of timed fertilizer applications on growth of Ilex crenata ‘Helleri’ cuttings was examined. At termination of the experiment, cuttings initially fertilized soon after roots were visible (week 4) were larger than cuttings for which fertilization was either delayed or withheld. Delaying the initiation of fertilization at weekly intervals after roots were visible resulted in lower dry weight per cutting as the delay in fertilization increased. Nitrogen (N) was found to accumulate in cuttings immediately after roots were first visible but not before. Fertilization before root appearance was of little practical benefit.