The major objectives of this symposium were to present procedures in current use for evaluating the elemental status of organic substrates and to identify those factors that have led to confusion in the interpretation of analyses. Selection of an acceptable standard procedure for adaptation as a routine test method could reduce conflicting interpretation of obtained results. However, none of the procedures presented can be performed with complete congruency. Although standardization may serve routine soil testing needs, it may not satisfy needs for organic media testing when exchangeable nutrient levels or precise concentrations accounting for substrate moisture content must be established. Procedures discussed in this symposium are all useful for meeting specific needs, and are presented in sufficient detail so that each procedure could be individually evaluated. The most prominent considerations expressed throughout the symposium are reemphasized as follows.
Ilex × `Nellie R. Stevens' holly, Rhododendron sp. `Hinodegeri' azalea and Pyracantha coccinea, scarlet firethorn rooted cuttings were potted in • 3.81 containers. Irrigation was applied by Dram rings daily, or every 2,4,or 6 days. Approximately 1000 ml of water were applied at each irrigation. Three container media, including pine bark, and pine bark amended with either Terra-Sorb AG synthetic moisture extender incorporated at 1.2 kg/m3 or Aqua-Gro G wetting agent incorporated at 0.9 kg/m3 plus monthly drenches of 700 ml of 2500 ppm Aqua-Gro L were compared for physical and chemical properties and plant growth responses. Decreasing irrigation decreased pH, increased nutrient leachate levels, and increased foliar tissue levels of N,P,K,Ca,and Fe in holly and azalea. Pyracantha top and root dry weight was reduced at 4 and 6 day irrigation intervals, holly top growth was reduced by 6 day and azalea had greatest shoot growth at 2 day irrigation and was reduced by other irrigation frequencies. Top growth of all 3 species and root growth of pyracantha was reduced in the pine bark treatment.
Research reports documenting phosphorus leaching from soilless container media has changed commercial nursery phosphorus fertilizing practices. However, rhododendron growers are concerned that phosphorus levels are adequate as plants begin setting flower buds in July and August. Medium solution of 10 to 15 ppm P are recommended. Five replicated leachate samples were collected from 6 phosphate sources for 11 weeks following surface application to 2 container grown rhododendron cultivars. Each fertilizer source wax blended to an analysis of 14.0N-11.2P-5.0K except a 14.0N-0P-5.0K control. Phosphate sources included Diammonium Phosphate, Triple superphosphate, Sulfur coated Diammonium Phosphate, Sulfur coated triple superphosphate, and a commercial rhododendron sulfur coated fertilizer. With the exception of control, all treatment leachate phosphorus levels ranged from 180 to 145 ppm two days and 85 to 75 ppm one week after application. All sources ranged from 45 to 10 ppm weeks 2-5 and were lower than 10 ppm weeks 7-11. Leachate levels of the control were below 10 ppm at all sample times. Bud set and foliar P levels were different among phosphate treatments, but growth index measurements were not significant.
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.
Many universities face tough decisions on how to allocate limited resources to serve a demanding clientele. Industry officials frequently perceive university researchers and extension specialists as losing touch with reality and working on irrelevant problems. In many situations, this perception is a result of the lack of communication among the parties involved. Research and Extension Commodity Overviews conducted by the College of Agriculture and Life Sciences at North Carolina State Univ. have proved to be an excellent way of improving communications between university personnel and the industries they support. This paper outlines the overview process and shows how this approach benefited the state's nursery industry and the university.
Freshly harvested, unstratified seeds of K. latifolia and R. maximum were treated with GA3 for 36 hours at concentrations of 0, 50, 200, and 1000 ppm, sown in multicell flats containing 3 bark: 1 sand medium (v/v), grown for 21 days in a greenhouse under 10-hour and 24-hour photoperiods and irrigated by mat, intermittent mist, or hand-sprinkling. Average germination was 79.8% for K. latifolia and 79.2% for R. maximum. Seed germination of K. latifolia was 90% under intermittent mist and 24-hour photoperiods. R. maximum germination was highest under intermittent mist watering (88%) with no difference between 10-hour and 24-hour photoperiods. Gibberellic acid (GA3) treatment had no effect on germination in either species.
Cuttings of three ornamental species [Ilex × ‘Nellie R. Stevens’, (I. aquifolium × I. cornuta) Van Lennep, × Cupressocyparis leylandii Jacks & Dall. ‘Haggerston Grey’, and Lagerstroemia indica L.] were inserted in 11 media to determine the effects of physical properties of propagation media on rooting response. The physical properties of seven propagation media were altered by manipulating particle size distribution of a 1 aged pine bark : 1 composted hardwood bark (v/v) medium. Four other propagation media were used for comparison. Container capacity air space ranged from 12% to 40%, and water held after drainage in the root zone ranged from 35% to 55%. Variation in rooting response of cuttings occurred, but differences could not be attributed to the physical properties of the various media. In addition, no relationship between rooting response and engineered combinations of hardwood bark and pine bark were detected.
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.
One-year-old Rhododendron L. `Nova Zembla' were grown in four container media infested with Phytophthora cinnamomi Rands. The media (all v/v) were pine bark, 3 pine bark:1 sand, 3 pine bark:1 peat, and 1 peat: 1 sand: 1 soil. After 20 weeks, plants were evaluated for root rot symptoms and the total porosity, air space, moisture-holding capacity, and bulk density were determined for all media. All media provided adequate moisture-holding capacity for container production of rhododendron in noninfested media. Shoot fresh weight in noninfested media was positively correlated with bulk density and water (percent by volume) held in the 1.0- to 5.0-kPa matric tension range and negatively correlated with total porosity and air space. Root rot severity was greatest in peat: sand: soil, intermediate in pine bark: peat, and least in pine bark and pine bark: sand. Root rot severity was negatively correlated with total porosity and air space and positively correlated with bulk density and water (percent by volume) held in the 5.0- to 10.0-kPa matric tension range.